9348 mii: duplicate 'const' declaration specifier

[unleashed.git] / usr / src / uts / common / io / winlockio.c

/*
 * CDDL HEADER START
 *
 * The contents of this file are subject to the terms of the
 * Common Development and Distribution License (the "License").
 * You may not use this file except in compliance with the License.
 *
 * You can obtain a copy of the license at usr/src/OPENSOLARIS.LICENSE
 * or http://www.opensolaris.org/os/licensing.
 * See the License for the specific language governing permissions
 * and limitations under the License.
 *
 * When distributing Covered Code, include this CDDL HEADER in each
 * file and include the License file at usr/src/OPENSOLARIS.LICENSE.
 * If applicable, add the following below this CDDL HEADER, with the
 * fields enclosed by brackets "[]" replaced with your own identifying
 * information: Portions Copyright [yyyy] [name of copyright owner]
 *
 * CDDL HEADER END
 */
/*
 * Copyright 2009 Sun Microsystems, Inc.  All rights reserved.
 * Use is subject to license terms.
 */


/*
 * This is the lock device driver.
 *
 * The lock driver provides a variation of inter-process mutexes with the
 * following twist in semantics:
 *      A waiter for a lock after a set timeout can "break" the lock and
 *      grab it from the current owner (without informing the owner).
 *
 * These semantics result in temporarily multiple processes thinking they
 * own the lock. This usually does not make sense for cases where locks are
 * used to protect a critical region and it is important to serialize access
 * to data structures. As breaking the lock will also lose the serialization
 * and result in corrupt data structures.
 *
 * The usage for winlock driver is primarily driven by the graphics system
 * when doing DGA (direct graphics access) graphics. The locks are used to
 * protect access to the frame buffer (presumably reflects back to the screen)
 * between competing processes that directly write to the screen as opposed
 * to going through the window server etc.
 * In this case, the result of breaking the lock at worst causes the screen
 * image to be distorted and is easily fixed by doing a "refresh"
 *
 * In well-behaved applications, the lock is held for a very short time and
 * the breaking semantics do not come into play. Not having this feature and
 * using normal inter-process mutexes will result in a misbehaved application
 * from grabbing the screen writing capability from the window manager and
 * effectively make the system look like it is hung (mouse pointer does not
 * move).
 *
 * A secondary aspect of the winlock driver is that it allows for extremely
 * fast lock acquire/release in cases where there is low contention. A memory
 * write is all that is needed (not even a function call). And the window
 * manager is the only DGA writer usually and this optimized for. Occasionally
 * some processes might do DGA graphics and cause kernel faults to handle
 * the contention/locking (and that has got to be slow!).
 *
 * The following IOCTLs are supported:
 *
 *   GRABPAGEALLOC:
 *      Compatibility with old cgsix device driver lockpage ioctls.
 *      Lockpages created this way must be an entire page for compatibility with
 *      older software.  This ioctl allocates a lock context with its own
 *      private lock page.  The unique "ident" that identifies this lock is
 *      returned.
 *
 *   GRABPAGEFREE:
 *      Compatibility with cgsix device driver lockpage ioctls.  This
 *      ioctl releases the lock context allocated by GRABPAGEALLOC.
 *
 *   GRABLOCKINFO:
 *      Returns a one-word flag.  '1' means that multiple clients may
 *      access this lock page.  Older device drivers returned '0',
 *      meaning that only two clients could access a lock page.
 *
 *   GRABATTACH:
 *      Not supported.  This ioctl would have grabbed all lock pages
 *      on behalf of the calling program.
 *
 *   WINLOCKALLOC:
 *      Allocate a lock context.  This ioctl accepts a key value.  as
 *      its argument.  If the key is zero, a new lock context is
 *      created, and its "ident" is returned.   If the key is nonzero,
 *      all existing contexts are checked to see if they match they
 *      key.  If a match is found, its reference count is incremented
 *      and its ident is returned, otherwise a new context is created
 *      and its ident is returned.
 *
 *   WINLOCKFREE:
 *      Free a lock context.  This ioctl accepts the ident of a lock
 *      context and decrements its reference count.  Once the reference
 *      count reaches zero *and* all mappings are released, the lock
 *      context is freed.  When all the lock context in the lock page are
 *      freed, the lock page is freed as well.
 *
 *   WINLOCKSETTIMEOUT:
 *      Set lock timeout for a context.  This ioctl accepts the ident
 *      of a lock context and a timeout value in milliseconds.
 *      Whenever lock contention occurs, the timer is started and the lock is
 *      broken after the timeout expires. If timeout value is zero, lock does
 *      not timeout.  This value will be rounded to the nearest clock
 *      tick, so don't try to use it for real-time control or something.
 *
 *   WINLOCKGETTIMEOUT:
 *      Get lock timeout from a context.
 *
 *   WINLOCKDUMP:
 *      Dump state of this device.
 *
 *
 * How /dev/winlock works:
 *
 *   Every lock context consists of two mappings for the client to the lock
 *   page.  These mappings are known as the "lock page" and "unlock page"
 *   to the client. The first mmap to the lock context (identified by the
 *   sy_ident field returns during alloc) allocates mapping to the lock page,
 *   the second mmap allocates a mapping to the unlock page.
 *      The mappings dont have to be ordered in virtual address space, but do
 *   need to be ordered in time. Mapping and unmapping of these lock and unlock
 *   pages should happen in pairs. Doing them one at a time or unmapping one
 *   and leaving one mapped etc cause undefined behaviors.
 *      The mappings are always of length PAGESIZE, and type MAP_SHARED.
 *
 *   The first ioctl is to ALLOC a lock, either based on a key (if trying to
 *      grab a preexisting lock) or 0 (gets a default new one)
 *      This ioctl returns a value in sy_ident which is needed to do the
 *      later mmaps and FREE/other ioctls.
 *
 *   The "page number" portion of the sy_ident needs to be passed as the
 *      file offset when doing an mmap for both the lock page and unlock page
 *
 *   The value returned by mmap ( a user virtual address) needs to be
 *      incremented by the "page offset" portion of sy_ident to obtain the
 *      pointer to the actual lock. (Skipping this step, does not cause any
 *      visible error, but the process will be using the wrong lock!)
 *
 *      On a fork(), the child process will inherit the mappings for free, but
 *   will not inherit the parent's lock ownership if any. The child should NOT
 *   do an explicit FREE on the lock context unless it did an explicit ALLOC.
 *      Only one process at a time is allowed to have a valid hat
 *   mapping to a lock page. This is enforced by this driver.
 *   A client acquires a lock by writing a '1' to the lock page.
 *   Note, that it is not necessary to read and veryify that the lock is '0'
 *      prior to writing a '1' in it.
 *   If it does not already have a valid mapping to that page, the driver
 *   takes a fault (devmap_access), loads the client mapping
 *   and allows the client to continue.  The client releases the lock by
 *   writing a '0' to the unlock page.  Again, if it does not have a valid
 *   mapping to the unlock page, the segment driver takes a fault,
 *   loads the mapping, and lets the client continue.  From this point
 *   forward, the client can make as many locks and unlocks as it
 *   wants, without any more faults into the kernel.
 *
 *   If a different process wants to acquire a lock, it takes a page fault
 *   when it writes the '1' to the lock page.  If the segment driver sees
 *   that the lock page contained a zero, then it invalidates the owner's
 *   mappings and gives the mappings to this process.
 *
 *   If there is already a '1' in the lock page when the second client
 *   tries to access the lock page, then a lock exists.  The segment
 *   driver sleeps the second client and, if applicable, starts the
 *   timeout on the lock.  The owner's mapping to the unlock page
 *   is invalidated so that the driver will be woken again when the owner
 *   releases the lock.
 *
 *   When the locking client finally writes a '0' to the unlock page, the
 *   segment driver takes another fault.  The client is given a valid
 *   mapping, not to the unlock page, but to the "trash page", and allowed
 *   to continue.  Meanwhile, the sleeping client is given a valid mapping
 *   to the lock/unlock pages and allowed to continue as well.
 *
 * RFE: There is a leak if process exits before freeing allocated locks
 * But currently not tracking which locks were allocated by which
 * process and we do not have a clean entry point into the driver
 * to do garbage collection. If the interface used a file descriptor for each
 * lock it allocs, then the driver can free up stuff in the _close routine
 */

#include <sys/types.h>          /* various type defn's */
#include <sys/debug.h>
#include <sys/param.h>          /* various kernel limits */
#include <sys/time.h>
#include <sys/errno.h>
#include <sys/kmem.h>           /* defines kmem_alloc() */
#include <sys/conf.h>           /* defines cdevsw */
#include <sys/file.h>           /* various file modes, etc. */
#include <sys/uio.h>            /* UIO stuff */
#include <sys/ioctl.h>
#include <sys/cred.h>           /* defines cred struct */
#include <sys/mman.h>           /* defines mmap(2) parameters */
#include <sys/stat.h>           /* defines S_IFCHR */
#include <sys/cmn_err.h>        /* use cmn_err */
#include <sys/ddi.h>            /* ddi stuff */
#include <sys/sunddi.h>         /* ddi stuff */
#include <sys/ddi_impldefs.h>   /* ddi stuff */
#include <sys/winlockio.h>      /* defines ioctls, flags, data structs */

static int      winlock_ioctl(dev_t, int, intptr_t, int, cred_t *, int *);
static int      winlock_devmap(dev_t, devmap_cookie_t, offset_t, size_t,
                        size_t *, uint_t);
static int      winlocksegmap(dev_t, off_t, struct as *, caddr_t *, off_t,
                        uint_t, uint_t, uint_t, cred_t *);

static struct cb_ops    winlock_cb_ops = {
        nulldev,                /* open */
        nulldev,                /* close */
        nodev,                  /* strategy */
        nodev,                  /* print */
        nodev,                  /* dump */
        nodev,                  /* read */
        nodev,                  /* write */
        winlock_ioctl,          /* ioctl */
        winlock_devmap,         /* devmap */
        nodev,                  /* mmap */
        winlocksegmap,          /* segmap */
        nochpoll,               /* poll */
        ddi_prop_op,            /* prop_op */
        NULL,                   /* streamtab */
        D_NEW|D_MP|D_DEVMAP,    /* Driver compatibility flag */
        0,                      /* rev */
        nodev,                  /* aread */
        nodev                   /* awrite */
};

static int winlock_info(dev_info_t *, ddi_info_cmd_t, void *, void **);
static int winlock_attach(dev_info_t *, ddi_attach_cmd_t);
static int winlock_detach(dev_info_t *, ddi_detach_cmd_t);

static struct dev_ops   winlock_ops = {
        DEVO_REV,
        0,                      /* refcount */
        winlock_info,           /* info */
        nulldev,                /* identify */
        nulldev,                /* probe */
        winlock_attach,         /* attach */
        winlock_detach,         /* detach */
        nodev,                  /* reset */
        &winlock_cb_ops,        /* driver ops */
        NULL,                   /* bus ops */
        NULL,                   /* power */
        ddi_quiesce_not_needed,         /* quiesce */
};

static int winlockmap_map(devmap_cookie_t, dev_t, uint_t, offset_t, size_t,
                void **);
static void winlockmap_unmap(devmap_cookie_t, void *, offset_t, size_t,
                devmap_cookie_t, void **, devmap_cookie_t, void **);
static int winlockmap_dup(devmap_cookie_t, void *,
                devmap_cookie_t, void **);
static int winlockmap_access(devmap_cookie_t, void *, offset_t, size_t,
                uint_t, uint_t);

static
struct devmap_callback_ctl winlockmap_ops = {
        DEVMAP_OPS_REV,
        winlockmap_map,
        winlockmap_access,
        winlockmap_dup,
        winlockmap_unmap,
};

#if DEBUG
static  int     lock_debug = 0;
#define DEBUGF(level, args)     { if (lock_debug >= (level)) cmn_err args; }
#else
#define DEBUGF(level, args)
#endif

/* Driver supports two styles of locks */
enum winlock_style { NEWSTYLE_LOCK, OLDSTYLE_LOCK };

/*
 * These structures describe a lock context.  We permit multiple
 * clients (not just two) to access a lock page
 *
 * The "cookie" identifies the lock context. It is the page number portion
 * sy_ident returned on lock allocation. Cookie is used in later ioctls.
 * "cookie" is lockid * PAGESIZE
 * "lockptr" is the kernel virtual address to the lock itself
 * The page offset portion of lockptr is the page offset portion of sy_ident
 */

/*
 * per-process information about locks.  This is the private field of
 * a devmap mapping.  Note that usually *two* mappings point to this.
 */

/*
 * Each process using winlock is associated with a segproc structure
 * In various driver entry points, we need to search to find the right
 * segproc structure (If we were using file handles for each lock this
 * would not have been necessary).
 * It would have been simple to use the process pid (and ddi_get_pid)
 * However, during fork devmap_dup is called in the parent process context
 * and using the pid complicates the code by introducing orphans.
 * Instead we use the as pointer for the process as a cookie
 * which requires delving into various non-DDI kosher structs
 */
typedef struct segproc {
        struct segproc  *next;          /* next client of this lock */
        struct seglock  *lp;            /* associated lock context */
        devmap_cookie_t lockseg;        /* lock mapping, if any */
        devmap_cookie_t unlockseg;      /* unlock mapping, if any */
        void            *tag;           /* process as pointer as tag */
        uint_t          flag;           /* see "flag bits" in winlockio.h */
} SegProc;

#define ID(sdp)         ((sdp)->tag)
#define CURPROC_ID      (void *)(curproc->p_as)

/* per lock context information */

typedef struct seglock {
        struct seglock  *next;          /* next lock */
        uint_t          sleepers;       /* nthreads sleeping on this lock */
        uint_t          alloccount;     /* how many times created? */
        uint_t          cookie;         /* mmap() offset (page #) into device */
        uint_t          key;            /* key, if any */
        enum winlock_style      style;  /* style of lock - OLDSTYLE, NEWSTYLE */
        clock_t         timeout;        /* sleep time in ticks */
        ddi_umem_cookie_t umem_cookie;  /* cookie for umem allocated memory */
        int             *lockptr;       /* kernel virtual addr of lock */
        struct segproc  *clients;       /* list of clients of this lock */
        struct segproc  *owner;         /* current owner of lock */
        kmutex_t        mutex;          /* mutex for lock */
        kcondvar_t      locksleep;      /* for sleeping on lock */
} SegLock;

#define LOCK(lp)        (*((lp)->lockptr))

/*
 * Number of locks that can fit in a page. Driver can support only that many.
 * For oldsytle locks, it is relatively easy to increase the limit as each
 * is in a separate page (MAX_LOCKS mostly serves to prevent runaway allocation
 * For newstyle locks, this is trickier as the code needs to allow for mapping
 * into the second or third page of the cookie for some locks.
 */
#define MAX_LOCKS       (PAGESIZE/sizeof (int))

#define LOCKTIME        3       /* Default lock timeout in seconds */


/* Protections setting for winlock user mappings */
#define WINLOCK_PROT    (PROT_READ|PROT_WRITE|PROT_USER)

/*
 * The trash page is where unwanted writes go
 * when a process is releasing a lock.
 */
static  ddi_umem_cookie_t trashpage_cookie = NULL;

/* For newstyle allocations a common page of locks is used */
static  caddr_t lockpage = NULL;
static  ddi_umem_cookie_t lockpage_cookie = NULL;

static  dev_info_t      *winlock_dip = NULL;
static  kmutex_t        winlock_mutex;

/*
 * winlock_mutex protects
 *      lock_list
 *      lock_free_list
 *      "next" field in SegLock
 *      next_lock
 *      trashpage_cookie
 *      lockpage & lockpage_cookie
 *
 * SegLock_mutex protects
 *      rest of fields in SegLock
 *      All fields in list of SegProc (lp->clients)
 *
 * Lock ordering is winlock_mutex->SegLock_mutex
 * During devmap/seg operations SegLock_mutex acquired without winlock_mutex
 *
 * During devmap callbacks, the pointer to SegProc is stored as the private
 * data in the devmap handle. This pointer will not go stale (i.e., the
 * SegProc getting deleted) as the SegProc is not deleted until both the
 * lockseg and unlockseg have been unmapped and the pointers stored in
 * the devmap handles have been NULL'ed.
 * But before this pointer is used to access any fields (other than the 'lp')
 * lp->mutex must be held.
 */

/*
 * The allocation code tries to allocate from lock_free_list
 * first, otherwise it uses kmem_zalloc.  When lock list is idle, all
 * locks in lock_free_list are kmem_freed
 */
static  SegLock *lock_list = NULL;              /* in-use locks */
static  SegLock *lock_free_list = NULL;         /* free locks */
static  int     next_lock = 0;                  /* next lock cookie */

/* Routines to find a lock in lock_list based on offset or key */
static SegLock *seglock_findlock(uint_t);
static SegLock *seglock_findkey(uint_t);

/* Routines to find and allocate SegProc structures */
static SegProc *seglock_find_specific(SegLock *, void *);
static SegProc *seglock_alloc_specific(SegLock *, void *);
#define seglock_findclient(lp)  seglock_find_specific((lp), CURPROC_ID)
#define seglock_allocclient(lp) seglock_alloc_specific((lp), CURPROC_ID)

/* Delete client from lock's client list */
static void seglock_deleteclient(SegLock *, SegProc *);
static void garbage_collect_lock(SegLock *, SegProc *);

/* Create a new lock */
static SegLock *seglock_createlock(enum winlock_style);
/* Destroy lock */
static void seglock_destroylock(SegLock *);
static void lock_destroyall(void);

/* Helper functions in winlockmap_access */
static int give_mapping(SegLock *, SegProc *, uint_t);
static int lock_giveup(SegLock *, int);
static int seglock_lockfault(devmap_cookie_t, SegProc *, SegLock *, uint_t);

/* routines called from ioctl */
static int seglock_graballoc(intptr_t, enum winlock_style, int);
static int seglock_grabinfo(intptr_t, int);
static int seglock_grabfree(intptr_t, int);
static int seglock_gettimeout(intptr_t, int);
static int seglock_settimeout(intptr_t, int);
static void seglock_dump_all(void);

static  int
winlock_attach(dev_info_t *devi, ddi_attach_cmd_t cmd)
{
        DEBUGF(1, (CE_CONT, "winlock_attach, devi=%p, cmd=%d\n",
            (void *)devi, (int)cmd));
        if (cmd != DDI_ATTACH)
                return (DDI_FAILURE);
        if (ddi_create_minor_node(devi, "winlock", S_IFCHR, 0, DDI_PSEUDO, 0)
            == DDI_FAILURE) {
                return (DDI_FAILURE);
        }
        winlock_dip = devi;
        ddi_report_dev(devi);
        return (DDI_SUCCESS);
}

/*ARGSUSED*/
static  int
winlock_detach(dev_info_t *devi, ddi_detach_cmd_t cmd)
{
        DEBUGF(1, (CE_CONT, "winlock_detach, devi=%p, cmd=%d\n",
            (void *)devi, (int)cmd));
        if (cmd != DDI_DETACH)
                return (DDI_FAILURE);

        mutex_enter(&winlock_mutex);
        if (lock_list != NULL) {
                mutex_exit(&winlock_mutex);
                return (DDI_FAILURE);
        }
        ASSERT(lock_free_list == NULL);

        DEBUGF(1, (CE_CONT, "detach freeing trashpage and lockpage\n"));
        /* destroy any common stuff created */
        if (trashpage_cookie != NULL) {
                ddi_umem_free(trashpage_cookie);
                trashpage_cookie = NULL;
        }
        if (lockpage != NULL) {
                ddi_umem_free(lockpage_cookie);
                lockpage = NULL;
                lockpage_cookie = NULL;
        }
        winlock_dip = NULL;
        mutex_exit(&winlock_mutex);
        return (DDI_SUCCESS);
}

/*ARGSUSED*/
static  int
winlock_info(dev_info_t *dip, ddi_info_cmd_t infocmd, void *arg, void **result)
{
        register int error;

        /* initialize result */
        *result = NULL;

        /* only valid instance (i.e., getminor) is 0 */
        if (getminor((dev_t)arg) >= 1)
                return (DDI_FAILURE);

        switch (infocmd) {
        case DDI_INFO_DEVT2DEVINFO:
                if (winlock_dip == NULL)
                        error = DDI_FAILURE;
                else {
                        *result = (void *)winlock_dip;
                        error = DDI_SUCCESS;
                }
                break;
        case DDI_INFO_DEVT2INSTANCE:
                *result = (void *)0;
                error = DDI_SUCCESS;
                break;
        default:
                error = DDI_FAILURE;
        }
        return (error);
}


/*ARGSUSED*/
int
winlock_ioctl(dev_t dev, int cmd, intptr_t arg, int mode,
        cred_t *cred, int *rval)
{
        DEBUGF(1, (CE_CONT, "winlockioctl: cmd=%d, arg=0x%p\n",
            cmd, (void *)arg));

        switch (cmd) {
        /*
         * ioctls that used to be handled by framebuffers (defined in fbio.h)
         * RFE: No code really calls the GRAB* ioctls now. Should EOL.
         */

        case GRABPAGEALLOC:
                return (seglock_graballoc(arg, OLDSTYLE_LOCK, mode));
        case GRABPAGEFREE:
                return (seglock_grabfree(arg, mode));
        case GRABLOCKINFO:
                return (seglock_grabinfo(arg, mode));
        case GRABATTACH:
                return (EINVAL); /* GRABATTACH is not supported (never was) */

        case WINLOCKALLOC:
                return (seglock_graballoc(arg, NEWSTYLE_LOCK, mode));
        case WINLOCKFREE:
                return (seglock_grabfree(arg, mode));
        case WINLOCKSETTIMEOUT:
                return (seglock_settimeout(arg, mode));
        case WINLOCKGETTIMEOUT:
                return (seglock_gettimeout(arg, mode));
        case WINLOCKDUMP:
                seglock_dump_all();
                return (0);

#ifdef DEBUG
        case (WIOC|255):
                lock_debug = arg;
                return (0);
#endif

        default:
                return (ENOTTY);                /* Why is this not EINVAL */
        }
}

int
winlocksegmap(
        dev_t   dev,            /* major:minor */
        off_t   off,            /* device offset from mmap(2) */
        struct as *as,          /* user's address space. */
        caddr_t *addr,          /* address from mmap(2) */
        off_t   len,            /* length from mmap(2) */
        uint_t  prot,           /* user wants this access */
        uint_t  maxprot,        /* this is the maximum the user can have */
        uint_t  flags,          /* flags from mmap(2) */
        cred_t  *cred)
{
        DEBUGF(1, (CE_CONT, "winlock_segmap off=%lx, len=0x%lx\n", off, len));

        /* Only MAP_SHARED mappings are supported */
        if ((flags & MAP_TYPE) == MAP_PRIVATE) {
                return (EINVAL);
        }

        /* Use devmap_setup to setup the mapping */
        return (devmap_setup(dev, (offset_t)off, as, addr, (size_t)len, prot,
            maxprot, flags, cred));
}

/*ARGSUSED*/
int
winlock_devmap(dev_t dev, devmap_cookie_t dhp, offset_t off, size_t len,
    size_t *maplen, uint_t model)
{
        SegLock *lp;
        int err;

        DEBUGF(1, (CE_CONT, "winlock devmap: off=%llx, len=%lx, dhp=%p\n",
            off, len, (void *)dhp));

        *maplen = 0;

        /* Check if the lock exists, i.e., has been created by alloc */
        /* off is the sy_ident returned in the alloc ioctl */
        if ((lp = seglock_findlock((uint_t)off)) == NULL) {
                return (ENXIO);
        }

        /*
         * The offset bits in mmap(2) offset has to be same as in lockptr
         * OR the offset should be 0 (i.e. masked off)
         */
        if (((off & PAGEOFFSET) != 0) &&
            ((off ^ (uintptr_t)(lp->lockptr)) & (offset_t)PAGEOFFSET) != 0) {
                DEBUGF(2, (CE_CONT,
                    "mmap offset %llx mismatch with lockptr %p\n",
                    off, (void *)lp->lockptr));
                mutex_exit(&lp->mutex); /* mutex held by seglock_findlock */
                return (EINVAL);
        }

        /* Only supports PAGESIZE length mappings */
        if (len != PAGESIZE) {
                mutex_exit(&lp->mutex); /* mutex held by seglock_findlock */
                return (EINVAL);
        }

        /*
         * Set up devmap to point at page associated with lock
         * RFE: At this point we dont know if this is a lockpage or unlockpage
         * a lockpage would not need DEVMAP_ALLOW_REMAP setting
         * We could have kept track of the mapping order here,
         * but devmap framework does not support storing any state in this
         * devmap callback as it does not callback for error cleanup if some
         * other error happens in the framework.
         * RFE: We should modify the winlock mmap interface so that the
         * user process marks in the offset passed in whether this is for a
         * lock or unlock mapping instead of guessing based on order of maps
         * This would cleanup other things (such as in fork)
         */
        if ((err = devmap_umem_setup(dhp, winlock_dip, &winlockmap_ops,
            lp->umem_cookie, 0, PAGESIZE, WINLOCK_PROT,
            DEVMAP_ALLOW_REMAP, 0)) < 0) {
                mutex_exit(&lp->mutex); /* held by seglock_findlock */
                return (err);
        }
        /*
         * No mappings are loaded to those segments yet. The correctness
         * of the winlock semantics depends on the devmap framework/seg_dev NOT
         * loading the translations without calling _access callback.
         */

        mutex_exit(&lp->mutex); /* mutex held by seglock_findlock */
        *maplen = PAGESIZE;
        return (0);
}

/*
 * This routine is called by the devmap framework after the devmap entry point
 * above and the mapping is setup in seg_dev.
 * We store the pointer to the per-process context in the devmap private data.
 */
/*ARGSUSED*/
static int
winlockmap_map(devmap_cookie_t dhp, dev_t dev, uint_t flags, offset_t off,
        size_t len, void **pvtp)
{
        SegLock *lp = seglock_findlock((uint_t)off); /* returns w/ mutex held */
        SegProc *sdp;

        ASSERT(len == PAGESIZE);

        /* Find the per-process context for this lock, alloc one if not found */
        sdp = seglock_allocclient(lp);

        /*
         * RFE: Determining which is a lock vs unlock seg is based on order
         * of mmaps, we should change that to be derivable from off
         */
        if (sdp->lockseg == NULL) {
                sdp->lockseg = dhp;
        } else if (sdp->unlockseg == NULL) {
                sdp->unlockseg = dhp;
        } else {
                /* attempting to map lock more than twice */
                mutex_exit(&lp->mutex); /* mutex held by seglock_findlock */
                return (ENOMEM);
        }

        *pvtp = sdp;
        mutex_exit(&lp->mutex); /* mutex held by seglock_findlock */
        return (DDI_SUCCESS);
}

/*
 * duplicate a segment, as in fork()
 * On fork, the child inherits the mappings to the lock
 *      lp->alloccount is NOT incremented, so child should not do a free().
 *      Semantics same as if done an alloc(), map(), map().
 *      This way it would work fine if doing an exec() variant later
 *      Child does not inherit any UFLAGS set in parent
 * The lock and unlock pages are started off unmapped, i.e., child does not
 *      own the lock.
 * The code assumes that the child process has a valid pid at this point
 * RFE: This semantics depends on fork not duplicating the hat mappings
 *      (which is the current implementation). To enforce it would need to
 *      call devmap_unload from here - not clear if that is allowed.
 */

static int
winlockmap_dup(devmap_cookie_t dhp, void *oldpvt, devmap_cookie_t new_dhp,
        void **newpvt)
{
        SegProc *sdp = (SegProc *)oldpvt;
        SegProc *ndp;
        SegLock *lp = sdp->lp;

        mutex_enter(&lp->mutex);
        ASSERT((dhp == sdp->lockseg) || (dhp == sdp->unlockseg));

        /*
         * Note: At this point, the child process does have a pid, but
         * the arguments passed to as_dup and hence to devmap_dup dont pass it
         * down. So we cannot use normal seglock_findclient - which finds the
         * parent sdp itself!
         * Instead we allocate the child's SegProc by using the child as pointer
         * RFE: we are using the as stucture which means peeking into the
         * devmap_cookie. This is not DDI-compliant. Need a compliant way of
         * getting at either the as or, better, a way to get the child's new pid
         */
        ndp = seglock_alloc_specific(lp,
            (void *)((devmap_handle_t *)new_dhp)->dh_seg->s_as);
        ASSERT(ndp != sdp);

        if (sdp->lockseg == dhp) {
                ASSERT(ndp->lockseg == NULL);
                ndp->lockseg = new_dhp;
        } else {
                ASSERT(sdp->unlockseg == dhp);
                ASSERT(ndp->unlockseg == NULL);
                ndp->unlockseg = new_dhp;
                if (sdp->flag & TRASHPAGE) {
                        ndp->flag |= TRASHPAGE;
                }
        }
        mutex_exit(&lp->mutex);
        *newpvt = (void *)ndp;
        return (0);
}


/*ARGSUSED*/
static void
winlockmap_unmap(devmap_cookie_t dhp, void *pvtp, offset_t off, size_t len,
        devmap_cookie_t new_dhp1, void **newpvtp1,
        devmap_cookie_t new_dhp2, void **newpvtp2)
{
        SegProc *sdp = (SegProc *)pvtp;
        SegLock *lp = sdp->lp;

        /*
         * We always create PAGESIZE length mappings, so there should never
         * be a partial unmapping case
         */
        ASSERT((new_dhp1 == NULL) && (new_dhp2 == NULL));

        mutex_enter(&lp->mutex);
        ASSERT((dhp == sdp->lockseg) || (dhp == sdp->unlockseg));
        /* make sure this process doesn't own the lock */
        if (sdp == lp->owner) {
                /*
                 * Not handling errors - i.e., errors in unloading mapping
                 * As part of unmapping hat/seg structure get torn down anyway
                 */
                (void) lock_giveup(lp, 0);
        }

        ASSERT(sdp != lp->owner);
        if (sdp->lockseg == dhp) {
                sdp->lockseg = NULL;
        } else {
                ASSERT(sdp->unlockseg == dhp);
                sdp->unlockseg = NULL;
                sdp->flag &= ~TRASHPAGE;        /* clear flag if set */
        }

        garbage_collect_lock(lp, sdp);
}

/*ARGSUSED*/
static int
winlockmap_access(devmap_cookie_t dhp, void *pvt, offset_t off, size_t len,
        uint_t type, uint_t rw)
{
        SegProc *sdp = (SegProc *)pvt;
        SegLock *lp = sdp->lp;
        int err;

        /* Driver handles only DEVMAP_ACCESS type of faults */
        if (type != DEVMAP_ACCESS)
                return (-1);

        mutex_enter(&lp->mutex);
        ASSERT((dhp == sdp->lockseg) || (dhp == sdp->unlockseg));

        /* should be using a SegProc that corresponds to current process */
        ASSERT(ID(sdp) == CURPROC_ID);

        /*
         * If process is faulting but does not have both segments mapped
         * return error (should cause a segv).
         * RFE: could give it a permanent trashpage
         */
        if ((sdp->lockseg == NULL) || (sdp->unlockseg == NULL)) {
                err = -1;
        } else {
                err = seglock_lockfault(dhp, sdp, lp, rw);
        }
        mutex_exit(&lp->mutex);
        return (err);
}

        /* INTERNAL ROUTINES START HERE */



/*
 * search the lock_list list for the specified cookie
 * The cookie is the sy_ident field returns by ALLOC ioctl.
 * This has two parts:
 * the pageoffset bits contain offset into the lock page.
 * the pagenumber bits contain the lock id.
 * The user code is supposed to pass in only the pagenumber portion
 *      (i.e. mask off the pageoffset bits). However the code below
 *      does the mask in case the users are not diligent
 * if found, returns with mutex for SegLock structure held
 */
static SegLock *
seglock_findlock(uint_t cookie)
{
        SegLock *lp;

        cookie &= (uint_t)PAGEMASK;   /* remove pageoffset bits to get cookie */
        mutex_enter(&winlock_mutex);
        for (lp = lock_list; lp != NULL; lp = lp->next) {
                mutex_enter(&lp->mutex);
                if (cookie == lp->cookie) {
                        break;  /* return with lp->mutex held */
                }
                mutex_exit(&lp->mutex);
        }
        mutex_exit(&winlock_mutex);
        return (lp);
}

/*
 * search the lock_list list for the specified non-zero key
 * if found, returns with lock for SegLock structure held
 */
static SegLock *
seglock_findkey(uint_t key)
{
        SegLock *lp;

        ASSERT(MUTEX_HELD(&winlock_mutex));
        /* The driver allows multiple locks with key 0, dont search */
        if (key == 0)
                return (NULL);
        for (lp = lock_list; lp != NULL; lp = lp->next) {
                mutex_enter(&lp->mutex);
                if (key == lp->key)
                        break;
                mutex_exit(&lp->mutex);
        }
        return (lp);
}

/*
 * Create a new lock context.
 * Returns with SegLock mutex held
 */

static SegLock *
seglock_createlock(enum winlock_style style)
{
        SegLock *lp;

        DEBUGF(3, (CE_CONT, "seglock_createlock: free_list=%p, next_lock %d\n",
            (void *)lock_free_list, next_lock));

        ASSERT(MUTEX_HELD(&winlock_mutex));
        if (lock_free_list != NULL) {
                lp = lock_free_list;
                lock_free_list = lp->next;
        } else if (next_lock >= MAX_LOCKS) {
                return (NULL);
        } else {
                lp = kmem_zalloc(sizeof (SegLock), KM_SLEEP);
                lp->cookie = (next_lock + 1) * (uint_t)PAGESIZE;
                mutex_init(&lp->mutex, NULL, MUTEX_DEFAULT, NULL);
                cv_init(&lp->locksleep, NULL, CV_DEFAULT, NULL);
                ++next_lock;
        }

        mutex_enter(&lp->mutex);
        ASSERT((lp->cookie/PAGESIZE) <= next_lock);

        if (style == OLDSTYLE_LOCK) {
                lp->lockptr = (int *)ddi_umem_alloc(PAGESIZE,
                    DDI_UMEM_SLEEP, &(lp->umem_cookie));
        } else {
                lp->lockptr = ((int *)lockpage) + ((lp->cookie/PAGESIZE) - 1);
                lp->umem_cookie = lockpage_cookie;
        }

        ASSERT(lp->lockptr != NULL);
        lp->style = style;
        lp->sleepers = 0;
        lp->alloccount = 1;
        lp->timeout = LOCKTIME*hz;
        lp->clients = NULL;
        lp->owner = NULL;
        LOCK(lp) = 0;
        lp->next = lock_list;
        lock_list = lp;
        return (lp);
}

/*
 * Routine to destory a lock structure.
 * This routine is called while holding the lp->mutex but not the
 * winlock_mutex.
 */

static void
seglock_destroylock(SegLock *lp)
{
        ASSERT(MUTEX_HELD(&lp->mutex));
        ASSERT(!MUTEX_HELD(&winlock_mutex));

        DEBUGF(3, (CE_CONT, "destroying lock cookie %d key %d\n",
            lp->cookie, lp->key));

        ASSERT(lp->alloccount == 0);
        ASSERT(lp->clients == NULL);
        ASSERT(lp->owner == NULL);
        ASSERT(lp->sleepers == 0);

        /* clean up/release fields in lp */
        if (lp->style == OLDSTYLE_LOCK) {
                ddi_umem_free(lp->umem_cookie);
        }
        lp->umem_cookie = NULL;
        lp->lockptr = NULL;
        lp->key = 0;

        /*
         * Reduce cookie by 1, makes it non page-aligned and invalid
         * This prevents any valid lookup from finding this lock
         * so when we drop the lock and regrab it it will still
         * be there and nobody else would have attached to it
         */
        lp->cookie--;

        /* Drop and reacquire mutexes in right order */
        mutex_exit(&lp->mutex);
        mutex_enter(&winlock_mutex);
        mutex_enter(&lp->mutex);

        /* reincrement the cookie to get the original valid cookie */
        lp->cookie++;
        ASSERT((lp->cookie & PAGEOFFSET) == 0);
        ASSERT(lp->alloccount == 0);
        ASSERT(lp->clients == NULL);
        ASSERT(lp->owner == NULL);
        ASSERT(lp->sleepers == 0);

        /* Remove lp from lock_list */
        if (lock_list == lp) {
                lock_list = lp->next;
        } else {
                SegLock *tmp = lock_list;
                while (tmp->next != lp) {
                        tmp = tmp->next;
                        ASSERT(tmp != NULL);
                }
                tmp->next = lp->next;
        }

        /* Add to lock_free_list */
        lp->next = lock_free_list;
        lock_free_list = lp;
        mutex_exit(&lp->mutex);

        /* Check if all locks deleted and cleanup */
        if (lock_list == NULL) {
                lock_destroyall();
        }

        mutex_exit(&winlock_mutex);
}

/* Routine to find a SegProc corresponding to the tag */

static SegProc *
seglock_find_specific(SegLock *lp, void *tag)
{
        SegProc *sdp;

        ASSERT(MUTEX_HELD(&lp->mutex));
        ASSERT(tag != NULL);
        for (sdp = lp->clients; sdp != NULL; sdp = sdp->next) {
                if (ID(sdp) == tag)
                        break;
        }
        return (sdp);
}

/* Routine to find (and if needed allocate) a SegProc corresponding to tag */

static SegProc *
seglock_alloc_specific(SegLock *lp, void *tag)
{
        SegProc *sdp;

        ASSERT(MUTEX_HELD(&lp->mutex));
        ASSERT(tag != NULL);

        /* Search and return if existing one found */
        sdp = seglock_find_specific(lp, tag);
        if (sdp != NULL)
                return (sdp);

        DEBUGF(3, (CE_CONT, "Allocating segproc structure for tag %p lock %d\n",
            tag, lp->cookie));

        /* Allocate a new SegProc */
        sdp = kmem_zalloc(sizeof (SegProc), KM_SLEEP);
        sdp->next = lp->clients;
        lp->clients = sdp;
        sdp->lp = lp;
        ID(sdp) = tag;
        return (sdp);
}

/*
 * search a context's client list for the given client and delete
 */

static void
seglock_deleteclient(SegLock *lp, SegProc *sdp)
{
        ASSERT(MUTEX_HELD(&lp->mutex));
        ASSERT(lp->owner != sdp);       /* Not current owner of lock */
        ASSERT(sdp->lockseg == NULL);   /* Mappings torn down */
        ASSERT(sdp->unlockseg == NULL);

        DEBUGF(3, (CE_CONT, "Deleting segproc structure for pid %d lock %d\n",
            ddi_get_pid(), lp->cookie));
        if (lp->clients == sdp) {
                lp->clients = sdp->next;
        } else {
                SegProc *tmp = lp->clients;
                while (tmp->next != sdp) {
                        tmp = tmp->next;
                        ASSERT(tmp != NULL);
                }
                tmp->next = sdp->next;
        }
        kmem_free(sdp, sizeof (SegProc));
}

/*
 * Routine to verify if a SegProc and SegLock
 * structures are empty/idle.
 * Destroys the structures if they are ready
 * Can be called with sdp == NULL if want to verify only the lock state
 * caller should hold the lp->mutex
 * and this routine drops the mutex
 */
static void
garbage_collect_lock(SegLock *lp, SegProc *sdp)
{
        ASSERT(MUTEX_HELD(&lp->mutex));
        /* see if both segments unmapped from client structure */
        if ((sdp != NULL) && (sdp->lockseg == NULL) && (sdp->unlockseg == NULL))
                seglock_deleteclient(lp, sdp);

        /* see if this is last client in the entire lock context */
        if ((lp->clients == NULL) && (lp->alloccount == 0)) {
                seglock_destroylock(lp);
        } else {
                mutex_exit(&lp->mutex);
        }
}


/* IOCTLS START HERE */

static int
seglock_grabinfo(intptr_t arg, int mode)
{
        int i = 1;

        /* multiple clients per lock supported - see comments up top */
        if (ddi_copyout((caddr_t)&i, (caddr_t)arg, sizeof (int), mode) != 0)
                return (EFAULT);
        return (0);
}

static int
seglock_graballoc(intptr_t arg, enum winlock_style style, int mode) /* IOCTL */
{
        struct seglock  *lp;
        uint_t          key;
        struct          winlockalloc wla;
        int             err;

        if (style == OLDSTYLE_LOCK) {
                key = 0;
        } else {
                if (ddi_copyin((caddr_t)arg, (caddr_t)&wla, sizeof (wla),
                    mode)) {
                        return (EFAULT);
                }
                key = wla.sy_key;
        }

        DEBUGF(3, (CE_CONT,
            "seglock_graballoc: key=%u, style=%d\n", key, style));

        mutex_enter(&winlock_mutex);
        /* Allocate lockpage on first new style alloc */
        if ((lockpage == NULL) && (style == NEWSTYLE_LOCK)) {
                lockpage = ddi_umem_alloc(PAGESIZE, DDI_UMEM_SLEEP,
                    &lockpage_cookie);
        }

        /* Allocate trashpage on first alloc (any style) */
        if (trashpage_cookie == NULL) {
                (void) ddi_umem_alloc(PAGESIZE, DDI_UMEM_TRASH | DDI_UMEM_SLEEP,
                    &trashpage_cookie);
        }

        if ((lp = seglock_findkey(key)) != NULL) {
                DEBUGF(2, (CE_CONT, "alloc: found lock key %d cookie %d\n",
                    key, lp->cookie));
                ++lp->alloccount;
        } else if ((lp = seglock_createlock(style)) != NULL) {
                DEBUGF(2, (CE_CONT, "alloc: created lock key %d cookie %d\n",
                    key, lp->cookie));
                lp->key = key;
        } else {
                DEBUGF(2, (CE_CONT, "alloc: cannot create lock key %d\n", key));
                mutex_exit(&winlock_mutex);
                return (ENOMEM);
        }
        ASSERT((lp != NULL) && MUTEX_HELD(&lp->mutex));

        mutex_exit(&winlock_mutex);

        if (style == OLDSTYLE_LOCK) {
                err = ddi_copyout((caddr_t)&lp->cookie, (caddr_t)arg,
                    sizeof (lp->cookie), mode);
        } else {
                wla.sy_ident = lp->cookie +
                    (uint_t)((uintptr_t)(lp->lockptr) & PAGEOFFSET);
                err = ddi_copyout((caddr_t)&wla, (caddr_t)arg,
                    sizeof (wla), mode);
        }

        if (err) {
                /* On error, should undo allocation */
                lp->alloccount--;

                /* Verify and delete if lock is unused now */
                garbage_collect_lock(lp, NULL);
                return (EFAULT);
        }

        mutex_exit(&lp->mutex);
        return (0);
}

static int
seglock_grabfree(intptr_t arg, int mode)        /* IOCTL */
{
        struct seglock  *lp;
        uint_t  offset;

        if (ddi_copyin((caddr_t)arg, &offset, sizeof (offset), mode)
            != 0) {
                return (EFAULT);
        }
        DEBUGF(2, (CE_CONT, "seglock_grabfree: offset=%u", offset));

        if ((lp = seglock_findlock(offset)) == NULL) {
                DEBUGF(2, (CE_CONT, "did not find lock\n"));
                return (EINVAL);
        }
        DEBUGF(3, (CE_CONT, " lock key %d, cookie %d, alloccount %d\n",
            lp->key, lp->cookie, lp->alloccount));

        if (lp->alloccount > 0)
                lp->alloccount--;

        /* Verify and delete if lock is unused now */
        garbage_collect_lock(lp, NULL);
        return (0);
}


/*
 * Sets timeout in lock and UFLAGS in client
 *      the UFLAGS are stored in the client structure and persistent only
 *      till the unmap of the lock pages. If the process sets UFLAGS
 *      does a map of the lock/unlock pages and unmaps them, the client
 *      structure will get deleted and the UFLAGS will be lost. The process
 *      will need to resetup the flags.
 */
static int
seglock_settimeout(intptr_t arg, int mode)      /* IOCTL */
{
        SegLock         *lp;
        SegProc         *sdp;
        struct winlocktimeout           wlt;

        if (ddi_copyin((caddr_t)arg, &wlt, sizeof (wlt), mode) != 0) {
                return (EFAULT);
        }

        if ((lp = seglock_findlock(wlt.sy_ident)) == NULL)
                return (EINVAL);

        lp->timeout = MSEC_TO_TICK_ROUNDUP(wlt.sy_timeout);
        /* if timeout modified, wake up any sleepers */
        if (lp->sleepers > 0) {
                cv_broadcast(&lp->locksleep);
        }

        /*
         * If the process is trying to set UFLAGS,
         *      Find the client segproc and allocate one if needed
         *      Set the flags preserving the kernel flags
         * If the process is clearing UFLAGS
         *      Find the client segproc but dont allocate one if does not exist
         */
        if (wlt.sy_flags & UFLAGS) {
                sdp = seglock_allocclient(lp);
                sdp->flag = sdp->flag & KFLAGS | wlt.sy_flags & UFLAGS;
        } else if ((sdp = seglock_findclient(lp)) != NULL) {
                sdp->flag = sdp->flag & KFLAGS;
                /* If clearing UFLAGS leaves the segment or lock idle, delete */
                garbage_collect_lock(lp, sdp);
                return (0);
        }
        mutex_exit(&lp->mutex); /* mutex held by seglock_findlock */
        return (0);
}

static int
seglock_gettimeout(intptr_t arg, int mode)
{
        SegLock         *lp;
        SegProc         *sdp;
        struct winlocktimeout           wlt;

        if (ddi_copyin((caddr_t)arg, &wlt, sizeof (wlt), mode) != 0)
                return (EFAULT);

        if ((lp = seglock_findlock(wlt.sy_ident)) == NULL)
                return (EINVAL);

        wlt.sy_timeout = TICK_TO_MSEC(lp->timeout);
        /*
         * If this process has an active allocated lock return those flags
         *      Dont allocate a client structure on gettimeout
         * If not, return 0.
         */
        if ((sdp = seglock_findclient(lp)) != NULL) {
                wlt.sy_flags = sdp->flag & UFLAGS;
        } else {
                wlt.sy_flags = 0;
        }
        mutex_exit(&lp->mutex); /* mutex held by seglock_findlock */

        if (ddi_copyout(&wlt, (caddr_t)arg, sizeof (wlt), mode) != 0)
                return (EFAULT);

        return (0);
}

/*
 * Handle lock segment faults here...
 *
 * This is where the magic happens.
 */

/* ARGSUSED */
static  int
seglock_lockfault(devmap_cookie_t dhp, SegProc *sdp, SegLock *lp, uint_t rw)
{
        SegProc *owner = lp->owner;
        int err;

        ASSERT(MUTEX_HELD(&lp->mutex));
        DEBUGF(3, (CE_CONT,
            "seglock_lockfault: hdl=%p, sdp=%p, lp=%p owner=%p\n",
            (void *)dhp, (void *)sdp, (void *)lp, (void *)owner));

        /* lockfault is always called with sdp in current process context */
        ASSERT(ID(sdp) == CURPROC_ID);

        /* If Lock has no current owner, give the mapping to new owner */
        if (owner == NULL) {
                DEBUGF(4, (CE_CONT, " lock has no current owner\n"));
                return (give_mapping(lp, sdp, rw));
        }

        if (owner == sdp) {
                /*
                 * Current owner is faulting on owned lock segment OR
                 * Current owner is faulting on unlock page and has no waiters
                 * Then can give the mapping to current owner
                 */
                if ((sdp->lockseg == dhp) || (lp->sleepers == 0)) {
                DEBUGF(4, (CE_CONT, "lock owner faulting\n"));
                return (give_mapping(lp, sdp, rw));
                } else {
                /*
                 * Owner must be writing to unlock page and there are waiters.
                 * other cases have been checked earlier.
                 * Release the lock, owner, and owners mappings
                 * As the owner is trying to write to the unlock page, leave
                 * it with a trashpage mapping and wake up the sleepers
                 */
                ASSERT((dhp == sdp->unlockseg) && (lp->sleepers != 0));
                DEBUGF(4, (CE_CONT, " owner fault on unlock seg w/ sleeper\n"));
                return (lock_giveup(lp, 1));
                }
        }

        ASSERT(owner != sdp);

        /*
         * If old owner faulting on trash unlock mapping,
         * load hat mappings to trash page
         * RFE: non-owners should NOT be faulting on unlock mapping as they
         * as first supposed to fault on the lock seg. We could give them
         * a trash page or return error.
         */
        if ((sdp->unlockseg == dhp) && (sdp->flag & TRASHPAGE)) {
                DEBUGF(4, (CE_CONT, " old owner reloads trash mapping\n"));
                return (devmap_load(sdp->unlockseg, lp->cookie, PAGESIZE,
                    DEVMAP_ACCESS, rw));
        }

        /*
         * Non-owner faulting. Need to check current LOCK state.
         *
         * Before reading lock value in LOCK(lp), we must make sure that
         * the owner cannot change its value before we change mappings
         * or else we could end up either with a hung process
         * or more than one process thinking they have the lock.
         * We do that by unloading the owner's mappings
         */
        DEBUGF(4, (CE_CONT, " owner loses mappings to check lock state\n"));
        err = devmap_unload(owner->lockseg, lp->cookie, PAGESIZE);
        err |= devmap_unload(owner->unlockseg, lp->cookie, PAGESIZE);
        if (err != 0)
                return (err);   /* unable to remove owner mapping */

        /*
         * If lock is not held, then current owner mappings were
         * unloaded above and we can give the lock to the new owner
         */
        if (LOCK(lp) == 0) {
                DEBUGF(4, (CE_CONT,
                    "Free lock (%p): Giving mapping to new owner %d\n",
                    (void *)lp, ddi_get_pid()));
                return (give_mapping(lp, sdp, rw));
        }

        DEBUGF(4, (CE_CONT, "  lock held, sleeping\n"));

        /*
         * A non-owning process tried to write (presumably to the lockpage,
         * but it doesn't matter) but the lock is held; we need to sleep for
         * the lock while there is an owner.
         */

        lp->sleepers++;
        while ((owner = lp->owner) != NULL) {
                int rval;

                if ((lp->timeout == 0) || (owner->flag & SY_NOTIMEOUT)) {
                        /*
                         * No timeout has been specified for this lock;
                         * we'll simply sleep on the condition variable.
                         */
                        rval = cv_wait_sig(&lp->locksleep, &lp->mutex);
                } else {
                        /*
                         * A timeout _has_ been specified for this lock. We need
                         * to wake up and possibly steal this lock if the owner
                         * does not let it go. Note that all sleepers on a lock
                         * with a timeout wait; the sleeper with the earliest
                         * timeout will wakeup, and potentially steal the lock
                         * Stealing the lock will cause a broadcast on the
                         * locksleep cv and thus kick the other timed waiters
                         * and cause everyone to restart in a new timedwait
                         */
                        rval = cv_reltimedwait_sig(&lp->locksleep,
                            &lp->mutex, lp->timeout, TR_CLOCK_TICK);
                }

                /*
                 * Timeout and still old owner - steal lock
                 * Force-Release lock and give old owner a trashpage mapping
                 */
                if ((rval == -1) && (lp->owner == owner)) {
                        /*
                         * if any errors in lock_giveup, go back and sleep/retry
                         * If successful, will break out of loop
                         */
                        cmn_err(CE_NOTE, "Process %d timed out on lock %d\n",
                            ddi_get_pid(), lp->cookie);
                        (void) lock_giveup(lp, 1);
                } else if (rval == 0) { /* signal pending */
                        cmn_err(CE_NOTE,
                            "Process %d signalled while waiting on lock %d\n",
                            ddi_get_pid(), lp->cookie);
                        lp->sleepers--;
                        return (FC_MAKE_ERR(EINTR));
                }
        }

        lp->sleepers--;
        /*
         * Give mapping to this process and save a fault later
         */
        return (give_mapping(lp, sdp, rw));
}

/*
 * Utility: give a valid mapping to lock and unlock pages to current process.
 * Caller responsible for unloading old owner's mappings
 */

static int
give_mapping(SegLock *lp, SegProc *sdp, uint_t rw)
{
        int err = 0;

        ASSERT(MUTEX_HELD(&lp->mutex));
        ASSERT(!((lp->owner == NULL) && (LOCK(lp) != 0)));
        /* give_mapping is always called with sdp in current process context */
        ASSERT(ID(sdp) == CURPROC_ID);

        /* remap any old trash mappings */
        if (sdp->flag & TRASHPAGE) {
                /* current owner should not have a trash mapping */
                ASSERT(sdp != lp->owner);

                DEBUGF(4, (CE_CONT,
                    "new owner %d remapping old trash mapping\n",
                    ddi_get_pid()));
                if ((err = devmap_umem_remap(sdp->unlockseg, winlock_dip,
                    lp->umem_cookie, 0, PAGESIZE, WINLOCK_PROT, 0, 0)) != 0) {
                        /*
                         * unable to remap old trash page,
                         * abort before changing owner
                         */
                        DEBUGF(4, (CE_CONT,
                            "aborting: error in umem_remap %d\n", err));
                        return (err);
                }
                sdp->flag &= ~TRASHPAGE;
        }

        /* we have a new owner now */
        lp->owner = sdp;

        if ((err = devmap_load(sdp->lockseg, lp->cookie, PAGESIZE,
            DEVMAP_ACCESS, rw)) != 0) {
                return (err);
        }
        DEBUGF(4, (CE_CONT, "new owner %d gets lock mapping", ddi_get_pid()));

        if (lp->sleepers) {
                /* Force unload unlock mapping if there are waiters */
                DEBUGF(4, (CE_CONT,
                    " lock has %d sleepers => remove unlock mapping\n",
                    lp->sleepers));
                err = devmap_unload(sdp->unlockseg, lp->cookie, PAGESIZE);
        } else {
                /*
                 * while here, give new owner a valid mapping to unlock
                 * page so we don't get called again.
                 */
                DEBUGF(4, (CE_CONT, " and unlock mapping\n"));
                err = devmap_load(sdp->unlockseg, lp->cookie, PAGESIZE,
                    DEVMAP_ACCESS, PROT_WRITE);
        }
        return (err);
}

/*
 * Unload owner's mappings, release the lock and wakeup any sleepers
 * If trash, then the old owner is given a trash mapping
 *      => old owner held lock too long and caused a timeout
 */
static int
lock_giveup(SegLock *lp, int trash)
{
        SegProc *owner = lp->owner;

        DEBUGF(4, (CE_CONT, "winlock_giveup: lp=%p, owner=%p, trash %d\n",
            (void *)lp, (void *)ID(lp->owner), trash));

        ASSERT(MUTEX_HELD(&lp->mutex));
        ASSERT(owner != NULL);

        /*
         * owner loses lockpage/unlockpage mappings and gains a
         * trashpage mapping, if needed.
         */
        if (!trash) {
                /*
                 * We do not handle errors in devmap_unload in the !trash case,
                 * as the process is attempting to unmap/exit or otherwise
                 * release the lock. Errors in unloading the mapping are not
                 * going to affect that (unmap does not take error return).
                 */
                (void) devmap_unload(owner->lockseg, lp->cookie, PAGESIZE);
                (void) devmap_unload(owner->unlockseg, lp->cookie, PAGESIZE);
        } else {
                int err;

                if (err = devmap_unload(owner->lockseg, lp->cookie, PAGESIZE)) {
                        /* error unloading lockseg mapping. abort giveup */
                        return (err);
                }

                /*
                 * old owner gets mapping to trash page so it can continue
                 * devmap_umem_remap does a hat_unload (and does it holding
                 * the right locks), so no need to devmap_unload on unlockseg
                 */
                if ((err = devmap_umem_remap(owner->unlockseg, winlock_dip,
                    trashpage_cookie, 0, PAGESIZE, WINLOCK_PROT, 0, 0)) != 0) {
                        /* error remapping to trash page, abort giveup */
                        return (err);
                }
                owner->flag |= TRASHPAGE;
                /*
                 * Preload mapping to trash page by calling devmap_load
                 * However, devmap_load can only be called on the faulting
                 * process context and not on the owner's process context
                 * we preload only if we happen to be in owner process context
                 * Other processes will fault on the unlock mapping
                 * and be given a trash mapping at that time.
                 */
                if (ID(owner) == CURPROC_ID) {
                        (void) devmap_load(owner->unlockseg, lp->cookie,
                            PAGESIZE, DEVMAP_ACCESS, PROT_WRITE);
                }
        }

        lp->owner = NULL;

        /* Clear the lock value in underlying page so new owner can grab it */
        LOCK(lp) = 0;

        if (lp->sleepers) {
                DEBUGF(4, (CE_CONT, "  waking up, lp=%p\n", (void *)lp));
                cv_broadcast(&lp->locksleep);
        }
        return (0);
}

/*
 * destroy all allocated memory.
 */

static void
lock_destroyall(void)
{
        SegLock *lp, *lpnext;

        ASSERT(MUTEX_HELD(&winlock_mutex));
        ASSERT(lock_list == NULL);

        DEBUGF(1, (CE_CONT, "Lock list empty. Releasing free list\n"));
        for (lp = lock_free_list; lp != NULL; lp = lpnext) {
                mutex_enter(&lp->mutex);
                lpnext =  lp->next;
                ASSERT(lp->clients == NULL);
                ASSERT(lp->owner == NULL);
                ASSERT(lp->alloccount == 0);
                mutex_destroy(&lp->mutex);
                cv_destroy(&lp->locksleep);
                kmem_free(lp, sizeof (SegLock));
        }
        lock_free_list = NULL;
        next_lock = 0;
}


/* RFE: create mdb walkers instead of dump routines? */
static void
seglock_dump_all(void)
{
        SegLock *lp;

        mutex_enter(&winlock_mutex);
        cmn_err(CE_CONT, "ID\tKEY\tNALLOC\tATTCH\tOWNED\tLOCK\tWAITER\n");

        cmn_err(CE_CONT, "Lock List:\n");
        for (lp = lock_list; lp != NULL; lp = lp->next) {
                mutex_enter(&lp->mutex);
                cmn_err(CE_CONT, "%d\t%d\t%u\t%c\t%c\t%c\t%d\n",
                    lp->cookie, lp->key, lp->alloccount,
                    lp->clients ? 'Y' : 'N',
                    lp->owner ? 'Y' : 'N',
                    lp->lockptr != 0 && LOCK(lp) ? 'Y' : 'N',
                    lp->sleepers);
                mutex_exit(&lp->mutex);
        }
        cmn_err(CE_CONT, "Free Lock List:\n");
        for (lp = lock_free_list; lp != NULL; lp = lp->next) {
                mutex_enter(&lp->mutex);
                cmn_err(CE_CONT, "%d\t%d\t%u\t%c\t%c\t%c\t%d\n",
                    lp->cookie, lp->key, lp->alloccount,
                    lp->clients ? 'Y' : 'N',
                    lp->owner ? 'Y' : 'N',
                    lp->lockptr != 0 && LOCK(lp) ? 'Y' : 'N',
                    lp->sleepers);
                mutex_exit(&lp->mutex);
        }

#ifdef DEBUG
        if (lock_debug < 3) {
                mutex_exit(&winlock_mutex);
                return;
        }

        for (lp = lock_list; lp != NULL; lp = lp->next) {
                SegProc *sdp;

                mutex_enter(&lp->mutex);
                cmn_err(CE_CONT,
                    "lock %p, key=%d, cookie=%d, nalloc=%u, lock=%d, wait=%d\n",
                    (void *)lp, lp->key, lp->cookie, lp->alloccount,
                    lp->lockptr != 0 ? LOCK(lp) : -1, lp->sleepers);

                cmn_err(CE_CONT,
                    "style=%d, lockptr=%p, timeout=%ld, clients=%p, owner=%p\n",
                    lp->style, (void *)lp->lockptr, lp->timeout,
                    (void *)lp->clients, (void *)lp->owner);


                for (sdp = lp->clients; sdp != NULL; sdp = sdp->next) {
                        cmn_err(CE_CONT, "  client %p%s, lp=%p, flag=%x, "
                            "process tag=%p, lockseg=%p, unlockseg=%p\n",
                            (void *)sdp, sdp == lp->owner ? " (owner)" : "",
                            (void *)sdp->lp, sdp->flag, (void *)ID(sdp),
                            (void *)sdp->lockseg, (void *)sdp->unlockseg);
                }
                mutex_exit(&lp->mutex);
        }
#endif
        mutex_exit(&winlock_mutex);
}

#include <sys/modctl.h>

static struct modldrv modldrv = {
        &mod_driverops,         /* Type of module.  This one is a driver */
        "Winlock Driver",       /* Name of the module */
        &winlock_ops,           /* driver ops */
};

static struct modlinkage modlinkage = {
        MODREV_1,
        (void *)&modldrv,
        0,
        0,
        0
};

int
_init(void)
{
        int e;

        mutex_init(&winlock_mutex, NULL, MUTEX_DEFAULT, NULL);
        e = mod_install(&modlinkage);
        if (e) {
                mutex_destroy(&winlock_mutex);
        }
        return (e);
}


int
_info(struct modinfo *modinfop)
{
        return (mod_info(&modlinkage, modinfop));
}

int
_fini(void)
{
        int     e;

        e = mod_remove(&modlinkage);
        if (e == 0) {
                mutex_destroy(&winlock_mutex);
        }
        return (e);
}