[PATCH] Add HOWTO do kernel development document to the Documentation directory

[linux-2.6/linux-acpi-2.6/ibm-acpi-2.6.git] / ipc / util.c

/*
 * linux/ipc/util.c
 * Copyright (C) 1992 Krishna Balasubramanian
 *
 * Sep 1997 - Call suser() last after "normal" permission checks so we
 *            get BSD style process accounting right.
 *            Occurs in several places in the IPC code.
 *            Chris Evans, <chris@ferret.lmh.ox.ac.uk>
 * Nov 1999 - ipc helper functions, unified SMP locking
 *            Manfred Spraul <manfreds@colorfullife.com>
 * Oct 2002 - One lock per IPC id. RCU ipc_free for lock-free grow_ary().
 *            Mingming Cao <cmm@us.ibm.com>
 */

#include <linux/config.h>
#include <linux/mm.h>
#include <linux/shm.h>
#include <linux/init.h>
#include <linux/msg.h>
#include <linux/smp_lock.h>
#include <linux/vmalloc.h>
#include <linux/slab.h>
#include <linux/highuid.h>
#include <linux/security.h>
#include <linux/rcupdate.h>
#include <linux/workqueue.h>
#include <linux/seq_file.h>
#include <linux/proc_fs.h>

#include <asm/unistd.h>

#include "util.h"

struct ipc_proc_iface {
        const char *path;
        const char *header;
        struct ipc_ids *ids;
        int (*show)(struct seq_file *, void *);
};

/**
 *      ipc_init        -       initialise IPC subsystem
 *
 *      The various system5 IPC resources (semaphores, messages and shared
 *      memory are initialised
 */
 
static int __init ipc_init(void)
{
        sem_init();
        msg_init();
        shm_init();
        return 0;
}
__initcall(ipc_init);

/**
 *      ipc_init_ids            -       initialise IPC identifiers
 *      @ids: Identifier set
 *      @size: Number of identifiers
 *
 *      Given a size for the ipc identifier range (limited below IPCMNI)
 *      set up the sequence range to use then allocate and initialise the
 *      array itself. 
 */
 
void __init ipc_init_ids(struct ipc_ids* ids, int size)
{
        int i;
        sema_init(&ids->sem,1);

        if(size > IPCMNI)
                size = IPCMNI;
        ids->in_use = 0;
        ids->max_id = -1;
        ids->seq = 0;
        {
                int seq_limit = INT_MAX/SEQ_MULTIPLIER;
                if(seq_limit > USHRT_MAX)
                        ids->seq_max = USHRT_MAX;
                 else
                        ids->seq_max = seq_limit;
        }

        ids->entries = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*size +
                                     sizeof(struct ipc_id_ary));

        if(ids->entries == NULL) {
                printk(KERN_ERR "ipc_init_ids() failed, ipc service disabled.\n");
                size = 0;
                ids->entries = &ids->nullentry;
        }
        ids->entries->size = size;
        for(i=0;i<size;i++)
                ids->entries->p[i] = NULL;
}

#ifdef CONFIG_PROC_FS
static struct file_operations sysvipc_proc_fops;
/**
 *      ipc_init_proc_interface -  Create a proc interface for sysipc types
 *                                 using a seq_file interface.
 *      @path: Path in procfs
 *      @header: Banner to be printed at the beginning of the file.
 *      @ids: ipc id table to iterate.
 *      @show: show routine.
 */
void __init ipc_init_proc_interface(const char *path, const char *header,
                                    struct ipc_ids *ids,
                                    int (*show)(struct seq_file *, void *))
{
        struct proc_dir_entry *pde;
        struct ipc_proc_iface *iface;

        iface = kmalloc(sizeof(*iface), GFP_KERNEL);
        if (!iface)
                return;
        iface->path     = path;
        iface->header   = header;
        iface->ids      = ids;
        iface->show     = show;

        pde = create_proc_entry(path,
                                S_IRUGO,        /* world readable */
                                NULL            /* parent dir */);
        if (pde) {
                pde->data = iface;
                pde->proc_fops = &sysvipc_proc_fops;
        } else {
                kfree(iface);
        }
}
#endif

/**
 *      ipc_findkey     -       find a key in an ipc identifier set     
 *      @ids: Identifier set
 *      @key: The key to find
 *      
 *      Requires ipc_ids.sem locked.
 *      Returns the identifier if found or -1 if not.
 */
 
int ipc_findkey(struct ipc_ids* ids, key_t key)
{
        int id;
        struct kern_ipc_perm* p;
        int max_id = ids->max_id;

        /*
         * rcu_dereference() is not needed here
         * since ipc_ids.sem is held
         */
        for (id = 0; id <= max_id; id++) {
                p = ids->entries->p[id];
                if(p==NULL)
                        continue;
                if (key == p->key)
                        return id;
        }
        return -1;
}

/*
 * Requires ipc_ids.sem locked
 */
static int grow_ary(struct ipc_ids* ids, int newsize)
{
        struct ipc_id_ary* new;
        struct ipc_id_ary* old;
        int i;
        int size = ids->entries->size;

        if(newsize > IPCMNI)
                newsize = IPCMNI;
        if(newsize <= size)
                return newsize;

        new = ipc_rcu_alloc(sizeof(struct kern_ipc_perm *)*newsize +
                            sizeof(struct ipc_id_ary));
        if(new == NULL)
                return size;
        new->size = newsize;
        memcpy(new->p, ids->entries->p, sizeof(struct kern_ipc_perm *)*size +
                                        sizeof(struct ipc_id_ary));
        for(i=size;i<newsize;i++) {
                new->p[i] = NULL;
        }
        old = ids->entries;

        /*
         * Use rcu_assign_pointer() to make sure the memcpyed contents
         * of the new array are visible before the new array becomes visible.
         */
        rcu_assign_pointer(ids->entries, new);

        ipc_rcu_putref(old);
        return newsize;
}

/**
 *      ipc_addid       -       add an IPC identifier
 *      @ids: IPC identifier set
 *      @new: new IPC permission set
 *      @size: new size limit for the id array
 *
 *      Add an entry 'new' to the IPC arrays. The permissions object is
 *      initialised and the first free entry is set up and the id assigned
 *      is returned. The list is returned in a locked state on success.
 *      On failure the list is not locked and -1 is returned.
 *
 *      Called with ipc_ids.sem held.
 */
 
int ipc_addid(struct ipc_ids* ids, struct kern_ipc_perm* new, int size)
{
        int id;

        size = grow_ary(ids,size);

        /*
         * rcu_dereference()() is not needed here since
         * ipc_ids.sem is held
         */
        for (id = 0; id < size; id++) {
                if(ids->entries->p[id] == NULL)
                        goto found;
        }
        return -1;
found:
        ids->in_use++;
        if (id > ids->max_id)
                ids->max_id = id;

        new->cuid = new->uid = current->euid;
        new->gid = new->cgid = current->egid;

        new->seq = ids->seq++;
        if(ids->seq > ids->seq_max)
                ids->seq = 0;

        spin_lock_init(&new->lock);
        new->deleted = 0;
        rcu_read_lock();
        spin_lock(&new->lock);
        ids->entries->p[id] = new;
        return id;
}

/**
 *      ipc_rmid        -       remove an IPC identifier
 *      @ids: identifier set
 *      @id: Identifier to remove
 *
 *      The identifier must be valid, and in use. The kernel will panic if
 *      fed an invalid identifier. The entry is removed and internal
 *      variables recomputed. The object associated with the identifier
 *      is returned.
 *      ipc_ids.sem and the spinlock for this ID is hold before this function
 *      is called, and remain locked on the exit.
 */
 
struct kern_ipc_perm* ipc_rmid(struct ipc_ids* ids, int id)
{
        struct kern_ipc_perm* p;
        int lid = id % SEQ_MULTIPLIER;
        if(lid >= ids->entries->size)
                BUG();

        /* 
         * do not need a rcu_dereference()() here to force ordering
         * on Alpha, since the ipc_ids.sem is held.
         */     
        p = ids->entries->p[lid];
        ids->entries->p[lid] = NULL;
        if(p==NULL)
                BUG();
        ids->in_use--;

        if (lid == ids->max_id) {
                do {
                        lid--;
                        if(lid == -1)
                                break;
                } while (ids->entries->p[lid] == NULL);
                ids->max_id = lid;
        }
        p->deleted = 1;
        return p;
}

/**
 *      ipc_alloc       -       allocate ipc space
 *      @size: size desired
 *
 *      Allocate memory from the appropriate pools and return a pointer to it.
 *      NULL is returned if the allocation fails
 */
 
void* ipc_alloc(int size)
{
        void* out;
        if(size > PAGE_SIZE)
                out = vmalloc(size);
        else
                out = kmalloc(size, GFP_KERNEL);
        return out;
}

/**
 *      ipc_free        -       free ipc space
 *      @ptr: pointer returned by ipc_alloc
 *      @size: size of block
 *
 *      Free a block created with ipc_alloc. The caller must know the size
 *      used in the allocation call.
 */

void ipc_free(void* ptr, int size)
{
        if(size > PAGE_SIZE)
                vfree(ptr);
        else
                kfree(ptr);
}

/*
 * rcu allocations:
 * There are three headers that are prepended to the actual allocation:
 * - during use: ipc_rcu_hdr.
 * - during the rcu grace period: ipc_rcu_grace.
 * - [only if vmalloc]: ipc_rcu_sched.
 * Their lifetime doesn't overlap, thus the headers share the same memory.
 * Unlike a normal union, they are right-aligned, thus some container_of
 * forward/backward casting is necessary:
 */
struct ipc_rcu_hdr
{
        int refcount;
        int is_vmalloc;
        void *data[0];
};


struct ipc_rcu_grace
{
        struct rcu_head rcu;
        /* "void *" makes sure alignment of following data is sane. */
        void *data[0];
};

struct ipc_rcu_sched
{
        struct work_struct work;
        /* "void *" makes sure alignment of following data is sane. */
        void *data[0];
};

#define HDRLEN_KMALLOC          (sizeof(struct ipc_rcu_grace) > sizeof(struct ipc_rcu_hdr) ? \
                                        sizeof(struct ipc_rcu_grace) : sizeof(struct ipc_rcu_hdr))
#define HDRLEN_VMALLOC          (sizeof(struct ipc_rcu_sched) > HDRLEN_KMALLOC ? \
                                        sizeof(struct ipc_rcu_sched) : HDRLEN_KMALLOC)

static inline int rcu_use_vmalloc(int size)
{
        /* Too big for a single page? */
        if (HDRLEN_KMALLOC + size > PAGE_SIZE)
                return 1;
        return 0;
}

/**
 *      ipc_rcu_alloc   -       allocate ipc and rcu space 
 *      @size: size desired
 *
 *      Allocate memory for the rcu header structure +  the object.
 *      Returns the pointer to the object.
 *      NULL is returned if the allocation fails. 
 */
 
void* ipc_rcu_alloc(int size)
{
        void* out;
        /* 
         * We prepend the allocation with the rcu struct, and
         * workqueue if necessary (for vmalloc). 
         */
        if (rcu_use_vmalloc(size)) {
                out = vmalloc(HDRLEN_VMALLOC + size);
                if (out) {
                        out += HDRLEN_VMALLOC;
                        container_of(out, struct ipc_rcu_hdr, data)->is_vmalloc = 1;
                        container_of(out, struct ipc_rcu_hdr, data)->refcount = 1;
                }
        } else {
                out = kmalloc(HDRLEN_KMALLOC + size, GFP_KERNEL);
                if (out) {
                        out += HDRLEN_KMALLOC;
                        container_of(out, struct ipc_rcu_hdr, data)->is_vmalloc = 0;
                        container_of(out, struct ipc_rcu_hdr, data)->refcount = 1;
                }
        }

        return out;
}

void ipc_rcu_getref(void *ptr)
{
        container_of(ptr, struct ipc_rcu_hdr, data)->refcount++;
}

/**
 * ipc_schedule_free - free ipc + rcu space
 * @head: RCU callback structure for queued work
 * 
 * Since RCU callback function is called in bh,
 * we need to defer the vfree to schedule_work
 */
static void ipc_schedule_free(struct rcu_head *head)
{
        struct ipc_rcu_grace *grace =
                container_of(head, struct ipc_rcu_grace, rcu);
        struct ipc_rcu_sched *sched =
                        container_of(&(grace->data[0]), struct ipc_rcu_sched, data[0]);

        INIT_WORK(&sched->work, vfree, sched);
        schedule_work(&sched->work);
}

/**
 * ipc_immediate_free - free ipc + rcu space
 * @head: RCU callback structure that contains pointer to be freed
 *
 * Free from the RCU callback context
 */
static void ipc_immediate_free(struct rcu_head *head)
{
        struct ipc_rcu_grace *free =
                container_of(head, struct ipc_rcu_grace, rcu);
        kfree(free);
}

void ipc_rcu_putref(void *ptr)
{
        if (--container_of(ptr, struct ipc_rcu_hdr, data)->refcount > 0)
                return;

        if (container_of(ptr, struct ipc_rcu_hdr, data)->is_vmalloc) {
                call_rcu(&container_of(ptr, struct ipc_rcu_grace, data)->rcu,
                                ipc_schedule_free);
        } else {
                call_rcu(&container_of(ptr, struct ipc_rcu_grace, data)->rcu,
                                ipc_immediate_free);
        }
}

/**
 *      ipcperms        -       check IPC permissions
 *      @ipcp: IPC permission set
 *      @flag: desired permission set.
 *
 *      Check user, group, other permissions for access
 *      to ipc resources. return 0 if allowed
 */
 
int ipcperms (struct kern_ipc_perm *ipcp, short flag)
{       /* flag will most probably be 0 or S_...UGO from <linux/stat.h> */
        int requested_mode, granted_mode;

        requested_mode = (flag >> 6) | (flag >> 3) | flag;
        granted_mode = ipcp->mode;
        if (current->euid == ipcp->cuid || current->euid == ipcp->uid)
                granted_mode >>= 6;
        else if (in_group_p(ipcp->cgid) || in_group_p(ipcp->gid))
                granted_mode >>= 3;
        /* is there some bit set in requested_mode but not in granted_mode? */
        if ((requested_mode & ~granted_mode & 0007) && 
            !capable(CAP_IPC_OWNER))
                return -1;

        return security_ipc_permission(ipcp, flag);
}

/*
 * Functions to convert between the kern_ipc_perm structure and the
 * old/new ipc_perm structures
 */

/**
 *      kernel_to_ipc64_perm    -       convert kernel ipc permissions to user
 *      @in: kernel permissions
 *      @out: new style IPC permissions
 *
 *      Turn the kernel object 'in' into a set of permissions descriptions
 *      for returning to userspace (out).
 */
 

void kernel_to_ipc64_perm (struct kern_ipc_perm *in, struct ipc64_perm *out)
{
        out->key        = in->key;
        out->uid        = in->uid;
        out->gid        = in->gid;
        out->cuid       = in->cuid;
        out->cgid       = in->cgid;
        out->mode       = in->mode;
        out->seq        = in->seq;
}

/**
 *      ipc64_perm_to_ipc_perm  -       convert old ipc permissions to new
 *      @in: new style IPC permissions
 *      @out: old style IPC permissions
 *
 *      Turn the new style permissions object in into a compatibility
 *      object and store it into the 'out' pointer.
 */
 
void ipc64_perm_to_ipc_perm (struct ipc64_perm *in, struct ipc_perm *out)
{
        out->key        = in->key;
        SET_UID(out->uid, in->uid);
        SET_GID(out->gid, in->gid);
        SET_UID(out->cuid, in->cuid);
        SET_GID(out->cgid, in->cgid);
        out->mode       = in->mode;
        out->seq        = in->seq;
}

/*
 * So far only shm_get_stat() calls ipc_get() via shm_get(), so ipc_get()
 * is called with shm_ids.sem locked.  Since grow_ary() is also called with
 * shm_ids.sem down(for Shared Memory), there is no need to add read 
 * barriers here to gurantee the writes in grow_ary() are seen in order 
 * here (for Alpha).
 *
 * However ipc_get() itself does not necessary require ipc_ids.sem down. So
 * if in the future ipc_get() is used by other places without ipc_ids.sem
 * down, then ipc_get() needs read memery barriers as ipc_lock() does.
 */
struct kern_ipc_perm* ipc_get(struct ipc_ids* ids, int id)
{
        struct kern_ipc_perm* out;
        int lid = id % SEQ_MULTIPLIER;
        if(lid >= ids->entries->size)
                return NULL;
        out = ids->entries->p[lid];
        return out;
}

struct kern_ipc_perm* ipc_lock(struct ipc_ids* ids, int id)
{
        struct kern_ipc_perm* out;
        int lid = id % SEQ_MULTIPLIER;
        struct ipc_id_ary* entries;

        rcu_read_lock();
        entries = rcu_dereference(ids->entries);
        if(lid >= entries->size) {
                rcu_read_unlock();
                return NULL;
        }
        out = entries->p[lid];
        if(out == NULL) {
                rcu_read_unlock();
                return NULL;
        }
        spin_lock(&out->lock);
        
        /* ipc_rmid() may have already freed the ID while ipc_lock
         * was spinning: here verify that the structure is still valid
         */
        if (out->deleted) {
                spin_unlock(&out->lock);
                rcu_read_unlock();
                return NULL;
        }
        return out;
}

void ipc_lock_by_ptr(struct kern_ipc_perm *perm)
{
        rcu_read_lock();
        spin_lock(&perm->lock);
}

void ipc_unlock(struct kern_ipc_perm* perm)
{
        spin_unlock(&perm->lock);
        rcu_read_unlock();
}

int ipc_buildid(struct ipc_ids* ids, int id, int seq)
{
        return SEQ_MULTIPLIER*seq + id;
}

int ipc_checkid(struct ipc_ids* ids, struct kern_ipc_perm* ipcp, int uid)
{
        if(uid/SEQ_MULTIPLIER != ipcp->seq)
                return 1;
        return 0;
}

#ifdef __ARCH_WANT_IPC_PARSE_VERSION


/**
 *      ipc_parse_version       -       IPC call version
 *      @cmd: pointer to command
 *
 *      Return IPC_64 for new style IPC and IPC_OLD for old style IPC. 
 *      The cmd value is turned from an encoding command and version into
 *      just the command code.
 */
 
int ipc_parse_version (int *cmd)
{
        if (*cmd & IPC_64) {
                *cmd ^= IPC_64;
                return IPC_64;
        } else {
                return IPC_OLD;
        }
}

#endif /* __ARCH_WANT_IPC_PARSE_VERSION */

#ifdef CONFIG_PROC_FS
static void *sysvipc_proc_next(struct seq_file *s, void *it, loff_t *pos)
{
        struct ipc_proc_iface *iface = s->private;
        struct kern_ipc_perm *ipc = it;
        loff_t p;

        /* If we had an ipc id locked before, unlock it */
        if (ipc && ipc != SEQ_START_TOKEN)
                ipc_unlock(ipc);

        /*
         * p = *pos - 1 (because id 0 starts at position 1)
         *          + 1 (because we increment the position by one)
         */
        for (p = *pos; p <= iface->ids->max_id; p++) {
                if ((ipc = ipc_lock(iface->ids, p)) != NULL) {
                        *pos = p + 1;
                        return ipc;
                }
        }

        /* Out of range - return NULL to terminate iteration */
        return NULL;
}

/*
 * File positions: pos 0 -> header, pos n -> ipc id + 1.
 * SeqFile iterator: iterator value locked shp or SEQ_TOKEN_START.
 */
static void *sysvipc_proc_start(struct seq_file *s, loff_t *pos)
{
        struct ipc_proc_iface *iface = s->private;
        struct kern_ipc_perm *ipc;
        loff_t p;

        /*
         * Take the lock - this will be released by the corresponding
         * call to stop().
         */
        down(&iface->ids->sem);

        /* pos < 0 is invalid */
        if (*pos < 0)
                return NULL;

        /* pos == 0 means header */
        if (*pos == 0)
                return SEQ_START_TOKEN;

        /* Find the (pos-1)th ipc */
        for (p = *pos - 1; p <= iface->ids->max_id; p++) {
                if ((ipc = ipc_lock(iface->ids, p)) != NULL) {
                        *pos = p + 1;
                        return ipc;
                }
        }
        return NULL;
}

static void sysvipc_proc_stop(struct seq_file *s, void *it)
{
        struct kern_ipc_perm *ipc = it;
        struct ipc_proc_iface *iface = s->private;

        /* If we had a locked segment, release it */
        if (ipc && ipc != SEQ_START_TOKEN)
                ipc_unlock(ipc);

        /* Release the lock we took in start() */
        up(&iface->ids->sem);
}

static int sysvipc_proc_show(struct seq_file *s, void *it)
{
        struct ipc_proc_iface *iface = s->private;

        if (it == SEQ_START_TOKEN)
                return seq_puts(s, iface->header);

        return iface->show(s, it);
}

static struct seq_operations sysvipc_proc_seqops = {
        .start = sysvipc_proc_start,
        .stop  = sysvipc_proc_stop,
        .next  = sysvipc_proc_next,
        .show  = sysvipc_proc_show,
};

static int sysvipc_proc_open(struct inode *inode, struct file *file) {
        int ret;
        struct seq_file *seq;

        ret = seq_open(file, &sysvipc_proc_seqops);
        if (!ret) {
                seq = file->private_data;
                seq->private = PDE(inode)->data;
        }
        return ret;
}

static struct file_operations sysvipc_proc_fops = {
        .open    = sysvipc_proc_open,
        .read    = seq_read,
        .llseek  = seq_lseek,
        .release = seq_release,
};
#endif /* CONFIG_PROC_FS */