3329 spa_sync() spends 10-20% of its time in spa_free_sync_cb()

[unleashed.git] / usr / src / uts / common / fs / lookup.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 (c) 1988, 2010, Oracle and/or its affiliates. All rights reserved.
 */

/*      Copyright (c) 1983, 1984, 1985, 1986, 1987, 1988, 1989 AT&T     */
/*        All Rights Reserved   */

/*
 * University Copyright- Copyright (c) 1982, 1986, 1988
 * The Regents of the University of California
 * All Rights Reserved
 *
 * University Acknowledgment- Portions of this document are derived from
 * software developed by the University of California, Berkeley, and its
 * contributors.
 */

#include <sys/types.h>
#include <sys/param.h>
#include <sys/systm.h>
#include <sys/cpuvar.h>
#include <sys/errno.h>
#include <sys/cred.h>
#include <sys/user.h>
#include <sys/uio.h>
#include <sys/vfs.h>
#include <sys/vnode.h>
#include <sys/pathname.h>
#include <sys/proc.h>
#include <sys/vtrace.h>
#include <sys/sysmacros.h>
#include <sys/debug.h>
#include <sys/dirent.h>
#include <c2/audit.h>
#include <sys/zone.h>
#include <sys/dnlc.h>
#include <sys/fs/snode.h>

/* Controls whether paths are stored with vnodes. */
int vfs_vnode_path = 1;

int
lookupname(
        char *fnamep,
        enum uio_seg seg,
        int followlink,
        vnode_t **dirvpp,
        vnode_t **compvpp)
{
        return (lookupnameatcred(fnamep, seg, followlink, dirvpp, compvpp, NULL,
            CRED()));
}

/*
 * Lookup the user file name,
 * Handle allocation and freeing of pathname buffer, return error.
 */
int
lookupnameatcred(
        char *fnamep,                   /* user pathname */
        enum uio_seg seg,               /* addr space that name is in */
        int followlink,                 /* follow sym links */
        vnode_t **dirvpp,               /* ret for ptr to parent dir vnode */
        vnode_t **compvpp,              /* ret for ptr to component vnode */
        vnode_t *startvp,               /* start path search from vp */
        cred_t *cr)                     /* credential */
{
        char namebuf[TYPICALMAXPATHLEN];
        struct pathname lookpn;
        int error;

        error = pn_get_buf(fnamep, seg, &lookpn, namebuf, sizeof (namebuf));
        if (error == 0) {
                error = lookuppnatcred(&lookpn, NULL, followlink,
                    dirvpp, compvpp, startvp, cr);
        }
        if (error == ENAMETOOLONG) {
                /*
                 * This thread used a pathname > TYPICALMAXPATHLEN bytes long.
                 */
                if (error = pn_get(fnamep, seg, &lookpn))
                        return (error);
                error = lookuppnatcred(&lookpn, NULL, followlink,
                    dirvpp, compvpp, startvp, cr);
                pn_free(&lookpn);
        }

        return (error);
}

int
lookupnameat(char *fnamep, enum uio_seg seg, int followlink,
    vnode_t **dirvpp, vnode_t **compvpp, vnode_t *startvp)
{
        return (lookupnameatcred(fnamep, seg, followlink, dirvpp, compvpp,
            startvp, CRED()));
}

int
lookuppn(
        struct pathname *pnp,
        struct pathname *rpnp,
        int followlink,
        vnode_t **dirvpp,
        vnode_t **compvpp)
{
        return (lookuppnatcred(pnp, rpnp, followlink, dirvpp, compvpp, NULL,
            CRED()));
}

/*
 * Lookup the user file name from a given vp, using a specific credential.
 */
int
lookuppnatcred(
        struct pathname *pnp,           /* pathname to lookup */
        struct pathname *rpnp,          /* if non-NULL, return resolved path */
        int followlink,                 /* (don't) follow sym links */
        vnode_t **dirvpp,               /* ptr for parent vnode */
        vnode_t **compvpp,              /* ptr for entry vnode */
        vnode_t *startvp,               /* start search from this vp */
        cred_t *cr)                     /* user credential */
{
        vnode_t *vp;    /* current directory vp */
        vnode_t *rootvp;
        proc_t *p = curproc;

        if (pnp->pn_pathlen == 0)
                return (ENOENT);

        mutex_enter(&p->p_lock);        /* for u_rdir and u_cdir */
        if ((rootvp = PTOU(p)->u_rdir) == NULL)
                rootvp = rootdir;
        else if (rootvp != rootdir)     /* no need to VN_HOLD rootdir */
                VN_HOLD(rootvp);

        if (pnp->pn_path[0] == '/') {
                vp = rootvp;
        } else {
                vp = (startvp == NULL) ? PTOU(p)->u_cdir : startvp;
        }
        VN_HOLD(vp);
        mutex_exit(&p->p_lock);

        /*
         * Skip over leading slashes
         */
        if (pnp->pn_path[0] == '/') {
                do {
                        pnp->pn_path++;
                        pnp->pn_pathlen--;
                } while (pnp->pn_path[0] == '/');
        }

        return (lookuppnvp(pnp, rpnp, followlink, dirvpp,
            compvpp, rootvp, vp, cr));
}

int
lookuppnat(struct pathname *pnp, struct pathname *rpnp,
    int followlink, vnode_t **dirvpp, vnode_t **compvpp,
    vnode_t *startvp)
{
        return (lookuppnatcred(pnp, rpnp, followlink, dirvpp, compvpp, startvp,
            CRED()));
}

/* Private flag to do our getcwd() dirty work */
#define LOOKUP_CHECKREAD        0x10
#define LOOKUP_MASK             (~LOOKUP_CHECKREAD)

/*
 * Starting at current directory, translate pathname pnp to end.
 * Leave pathname of final component in pnp, return the vnode
 * for the final component in *compvpp, and return the vnode
 * for the parent of the final component in dirvpp.
 *
 * This is the central routine in pathname translation and handles
 * multiple components in pathnames, separating them at /'s.  It also
 * implements mounted file systems and processes symbolic links.
 *
 * vp is the vnode where the directory search should start.
 *
 * Reference counts: vp must be held prior to calling this function.  rootvp
 * should only be held if rootvp != rootdir.
 */
int
lookuppnvp(
        struct pathname *pnp,           /* pathname to lookup */
        struct pathname *rpnp,          /* if non-NULL, return resolved path */
        int flags,                      /* follow symlinks */
        vnode_t **dirvpp,               /* ptr for parent vnode */
        vnode_t **compvpp,              /* ptr for entry vnode */
        vnode_t *rootvp,                /* rootvp */
        vnode_t *vp,                    /* directory to start search at */
        cred_t *cr)                     /* user's credential */
{
        vnode_t *cvp;   /* current component vp */
        vnode_t *tvp;   /* addressable temp ptr */
        char component[MAXNAMELEN];     /* buffer for component (incl null) */
        int error;
        int nlink;
        int lookup_flags;
        struct pathname presrvd; /* case preserved name */
        struct pathname *pp = NULL;
        vnode_t *startvp;
        vnode_t *zonevp = curproc->p_zone->zone_rootvp;         /* zone root */
        int must_be_directory = 0;
        boolean_t retry_with_kcred;
        uint32_t auditing = AU_AUDITING();

        CPU_STATS_ADDQ(CPU, sys, namei, 1);
        nlink = 0;
        cvp = NULL;
        if (rpnp)
                rpnp->pn_pathlen = 0;

        lookup_flags = dirvpp ? LOOKUP_DIR : 0;
        if (flags & FIGNORECASE) {
                lookup_flags |= FIGNORECASE;
                pn_alloc(&presrvd);
                pp = &presrvd;
        }

        if (auditing)
                audit_anchorpath(pnp, vp == rootvp);

        /*
         * Eliminate any trailing slashes in the pathname.
         * If there are any, we must follow all symlinks.
         * Also, we must guarantee that the last component is a directory.
         */
        if (pn_fixslash(pnp)) {
                flags |= FOLLOW;
                must_be_directory = 1;
        }

        startvp = vp;
next:
        retry_with_kcred = B_FALSE;

        /*
         * Make sure we have a directory.
         */
        if (vp->v_type != VDIR) {
                error = ENOTDIR;
                goto bad;
        }

        if (rpnp && VN_CMP(vp, rootvp))
                (void) pn_set(rpnp, "/");

        /*
         * Process the next component of the pathname.
         */
        if (error = pn_getcomponent(pnp, component)) {
                goto bad;
        }

        /*
         * Handle "..": two special cases.
         * 1. If we're at the root directory (e.g. after chroot or
         *    zone_enter) then change ".." to "." so we can't get
         *    out of this subtree.
         * 2. If this vnode is the root of a mounted file system,
         *    then replace it with the vnode that was mounted on
         *    so that we take the ".." in the other file system.
         */
        if (component[0] == '.' && component[1] == '.' && component[2] == 0) {
checkforroot:
                if (VN_CMP(vp, rootvp) || VN_CMP(vp, zonevp)) {
                        component[1] = '\0';
                } else if (vp->v_flag & VROOT) {
                        vfs_t *vfsp;
                        cvp = vp;

                        /*
                         * While we deal with the vfs pointer from the vnode
                         * the filesystem could have been forcefully unmounted
                         * and the vnode's v_vfsp could have been invalidated
                         * by VFS_UNMOUNT. Hence, we cache v_vfsp and use it
                         * with vfs_rlock_wait/vfs_unlock.
                         * It is safe to use the v_vfsp even it is freed by
                         * VFS_UNMOUNT because vfs_rlock_wait/vfs_unlock
                         * do not dereference v_vfsp. It is just used as a
                         * magic cookie.
                         * One more corner case here is the memory getting
                         * reused for another vfs structure. In this case
                         * lookuppnvp's vfs_rlock_wait will succeed, domount's
                         * vfs_lock will fail and domount will bail out with an
                         * error (EBUSY).
                         */
                        vfsp = cvp->v_vfsp;

                        /*
                         * This lock is used to synchronize
                         * mounts/unmounts and lookups.
                         * Threads doing mounts/unmounts hold the
                         * writers version vfs_lock_wait().
                         */

                        vfs_rlock_wait(vfsp);

                        /*
                         * If this vnode is on a file system that
                         * has been forcibly unmounted,
                         * we can't proceed. Cancel this operation
                         * and return EIO.
                         *
                         * vfs_vnodecovered is NULL if unmounted.
                         * Currently, nfs uses VFS_UNMOUNTED to
                         * check if it's a forced-umount. Keep the
                         * same checking here as well even though it
                         * may not be needed.
                         */
                        if (((vp = cvp->v_vfsp->vfs_vnodecovered) == NULL) ||
                            (cvp->v_vfsp->vfs_flag & VFS_UNMOUNTED)) {
                                vfs_unlock(vfsp);
                                VN_RELE(cvp);
                                if (pp)
                                        pn_free(pp);
                                return (EIO);
                        }
                        VN_HOLD(vp);
                        vfs_unlock(vfsp);
                        VN_RELE(cvp);
                        cvp = NULL;
                        /*
                         * Crossing mount points. For eg: We are doing
                         * a lookup of ".." for file systems root vnode
                         * mounted here, and VOP_LOOKUP() (with covered vnode)
                         * will be on underlying file systems mount point
                         * vnode. Set retry_with_kcred flag as we might end
                         * up doing VOP_LOOKUP() with kcred if required.
                         */
                        retry_with_kcred = B_TRUE;
                        goto checkforroot;
                }
        }

        /*
         * LOOKUP_CHECKREAD is a private flag used by vnodetopath() to indicate
         * that we need to have read permission on every directory in the entire
         * path.  This is used to ensure that a forward-lookup of a cached value
         * has the same effect as a reverse-lookup when the cached value cannot
         * be found.
         */
        if ((flags & LOOKUP_CHECKREAD) &&
            (error = VOP_ACCESS(vp, VREAD, 0, cr, NULL)) != 0)
                goto bad;

        /*
         * Perform a lookup in the current directory.
         */
        error = VOP_LOOKUP(vp, component, &tvp, pnp, lookup_flags,
            rootvp, cr, NULL, NULL, pp);

        /*
         * Retry with kcred - If crossing mount points & error is EACCES.
         *
         * If we are crossing mount points here and doing ".." lookup,
         * VOP_LOOKUP() might fail if the underlying file systems
         * mount point has no execute permission. In cases like these,
         * we retry VOP_LOOKUP() by giving as much privilage as possible
         * by passing kcred credentials.
         *
         * In case of hierarchical file systems, passing kcred still may
         * or may not work.
         * For eg: UFS FS --> Mount NFS FS --> Again mount UFS on some
         *                      directory inside NFS FS.
         */
        if ((error == EACCES) && retry_with_kcred)
                error = VOP_LOOKUP(vp, component, &tvp, pnp, lookup_flags,
                    rootvp, zone_kcred(), NULL, NULL, pp);

        cvp = tvp;
        if (error) {
                cvp = NULL;
                /*
                 * On error, return hard error if
                 * (a) we're not at the end of the pathname yet, or
                 * (b) the caller didn't want the parent directory, or
                 * (c) we failed for some reason other than a missing entry.
                 */
                if (pn_pathleft(pnp) || dirvpp == NULL || error != ENOENT)
                        goto bad;
                if (auditing) { /* directory access */
                        if (error = audit_savepath(pnp, vp, vp, error, cr))
                                goto bad_noaudit;
                }

                pn_setlast(pnp);
                /*
                 * We inform the caller that the desired entry must be
                 * a directory by adding a '/' to the component name.
                 */
                if (must_be_directory && (error = pn_addslash(pnp)) != 0)
                        goto bad;
                *dirvpp = vp;
                if (compvpp != NULL)
                        *compvpp = NULL;
                if (rootvp != rootdir)
                        VN_RELE(rootvp);
                if (pp)
                        pn_free(pp);
                return (0);
        }

        /*
         * Traverse mount points.
         * XXX why don't we need to hold a read lock here (call vn_vfsrlock)?
         * What prevents a concurrent update to v_vfsmountedhere?
         *      Possible answer: if mounting, we might not see the mount
         *      if it is concurrently coming into existence, but that's
         *      really not much different from the thread running a bit slower.
         *      If unmounting, we may get into traverse() when we shouldn't,
         *      but traverse() will catch this case for us.
         *      (For this to work, fetching v_vfsmountedhere had better
         *      be atomic!)
         */
        if (vn_mountedvfs(cvp) != NULL) {
                tvp = cvp;
                if ((error = traverse(&tvp)) != 0) {
                        /*
                         * It is required to assign cvp here, because
                         * traverse() will return a held vnode which
                         * may different than the vnode that was passed
                         * in (even in the error case).  If traverse()
                         * changes the vnode it releases the original,
                         * and holds the new one.
                         */
                        cvp = tvp;
                        goto bad;
                }
                cvp = tvp;
        }

        /*
         * If we hit a symbolic link and there is more path to be
         * translated or this operation does not wish to apply
         * to a link, then place the contents of the link at the
         * front of the remaining pathname.
         */
        if (cvp->v_type == VLNK && ((flags & FOLLOW) || pn_pathleft(pnp))) {
                struct pathname linkpath;

                if (++nlink > MAXSYMLINKS) {
                        error = ELOOP;
                        goto bad;
                }
                pn_alloc(&linkpath);
                if (error = pn_getsymlink(cvp, &linkpath, cr)) {
                        pn_free(&linkpath);
                        goto bad;
                }

                if (auditing)
                        audit_symlink(pnp, &linkpath);

                if (pn_pathleft(&linkpath) == 0)
                        (void) pn_set(&linkpath, ".");
                error = pn_insert(pnp, &linkpath, strlen(component));
                pn_free(&linkpath);
                if (error)
                        goto bad;
                VN_RELE(cvp);
                cvp = NULL;
                if (pnp->pn_pathlen == 0) {
                        error = ENOENT;
                        goto bad;
                }
                if (pnp->pn_path[0] == '/') {
                        do {
                                pnp->pn_path++;
                                pnp->pn_pathlen--;
                        } while (pnp->pn_path[0] == '/');
                        VN_RELE(vp);
                        vp = rootvp;
                        VN_HOLD(vp);
                }
                if (auditing)
                        audit_anchorpath(pnp, vp == rootvp);
                if (pn_fixslash(pnp)) {
                        flags |= FOLLOW;
                        must_be_directory = 1;
                }
                goto next;
        }

        /*
         * If rpnp is non-NULL, remember the resolved path name therein.
         * Do not include "." components.  Collapse occurrences of
         * "previous/..", so long as "previous" is not itself "..".
         * Exhausting rpnp results in error ENAMETOOLONG.
         */
        if (rpnp && strcmp(component, ".") != 0) {
                size_t len;

                if (strcmp(component, "..") == 0 &&
                    rpnp->pn_pathlen != 0 &&
                    !((rpnp->pn_pathlen > 2 &&
                    strncmp(rpnp->pn_path+rpnp->pn_pathlen-3, "/..", 3) == 0) ||
                    (rpnp->pn_pathlen == 2 &&
                    strncmp(rpnp->pn_path, "..", 2) == 0))) {
                        while (rpnp->pn_pathlen &&
                            rpnp->pn_path[rpnp->pn_pathlen-1] != '/')
                                rpnp->pn_pathlen--;
                        if (rpnp->pn_pathlen > 1)
                                rpnp->pn_pathlen--;
                        rpnp->pn_path[rpnp->pn_pathlen] = '\0';
                } else {
                        if (rpnp->pn_pathlen != 0 &&
                            rpnp->pn_path[rpnp->pn_pathlen-1] != '/')
                                rpnp->pn_path[rpnp->pn_pathlen++] = '/';
                        if (flags & FIGNORECASE) {
                                /*
                                 * Return the case-preserved name
                                 * within the resolved path.
                                 */
                                error = copystr(pp->pn_buf,
                                    rpnp->pn_path + rpnp->pn_pathlen,
                                    rpnp->pn_bufsize - rpnp->pn_pathlen, &len);
                        } else {
                                error = copystr(component,
                                    rpnp->pn_path + rpnp->pn_pathlen,
                                    rpnp->pn_bufsize - rpnp->pn_pathlen, &len);
                        }
                        if (error)      /* copystr() returns ENAMETOOLONG */
                                goto bad;
                        rpnp->pn_pathlen += (len - 1);
                        ASSERT(rpnp->pn_bufsize > rpnp->pn_pathlen);
                }
        }

        /*
         * If no more components, return last directory (if wanted) and
         * last component (if wanted).
         */
        if (pn_pathleft(pnp) == 0) {
                /*
                 * If there was a trailing slash in the pathname,
                 * make sure the last component is a directory.
                 */
                if (must_be_directory && cvp->v_type != VDIR) {
                        error = ENOTDIR;
                        goto bad;
                }
                if (dirvpp != NULL) {
                        /*
                         * Check that we have the real parent and not
                         * an alias of the last component.
                         */
                        if (vn_compare(vp, cvp)) {
                                if (auditing)
                                        (void) audit_savepath(pnp, cvp, vp,
                                            EINVAL, cr);
                                pn_setlast(pnp);
                                VN_RELE(vp);
                                VN_RELE(cvp);
                                if (rootvp != rootdir)
                                        VN_RELE(rootvp);
                                if (pp)
                                        pn_free(pp);
                                return (EINVAL);
                        }
                        *dirvpp = vp;
                } else
                        VN_RELE(vp);
                if (auditing)
                        (void) audit_savepath(pnp, cvp, vp, 0, cr);
                if (pnp->pn_path == pnp->pn_buf)
                        (void) pn_set(pnp, ".");
                else
                        pn_setlast(pnp);
                if (rpnp) {
                        if (VN_CMP(cvp, rootvp))
                                (void) pn_set(rpnp, "/");
                        else if (rpnp->pn_pathlen == 0)
                                (void) pn_set(rpnp, ".");
                }

                if (compvpp != NULL)
                        *compvpp = cvp;
                else
                        VN_RELE(cvp);
                if (rootvp != rootdir)
                        VN_RELE(rootvp);
                if (pp)
                        pn_free(pp);
                return (0);
        }

        /*
         * Skip over slashes from end of last component.
         */
        while (pnp->pn_path[0] == '/') {
                pnp->pn_path++;
                pnp->pn_pathlen--;
        }

        /*
         * Searched through another level of directory:
         * release previous directory handle and save new (result
         * of lookup) as current directory.
         */
        VN_RELE(vp);
        vp = cvp;
        cvp = NULL;
        goto next;

bad:
        if (auditing)   /* reached end of path */
                (void) audit_savepath(pnp, cvp, vp, error, cr);
bad_noaudit:
        /*
         * Error.  Release vnodes and return.
         */
        if (cvp)
                VN_RELE(cvp);
        /*
         * If the error was ESTALE and the current directory to look in
         * was the root for this lookup, the root for a mounted file
         * system, or the starting directory for lookups, then
         * return ENOENT instead of ESTALE.  In this case, no recovery
         * is possible by the higher level.  If ESTALE was returned for
         * some intermediate directory along the path, then recovery
         * is potentially possible and retrying from the higher level
         * will either correct the situation by purging stale cache
         * entries or eventually get back to the point where no recovery
         * is possible.
         */
        if (error == ESTALE &&
            (VN_CMP(vp, rootvp) || (vp->v_flag & VROOT) || vp == startvp))
                error = ENOENT;
        VN_RELE(vp);
        if (rootvp != rootdir)
                VN_RELE(rootvp);
        if (pp)
                pn_free(pp);
        return (error);
}

/*
 * Traverse a mount point.  Routine accepts a vnode pointer as a reference
 * parameter and performs the indirection, releasing the original vnode.
 */
int
traverse(vnode_t **cvpp)
{
        int error = 0;
        vnode_t *cvp;
        vnode_t *tvp;
        vfs_t *vfsp;

        cvp = *cvpp;

        /*
         * If this vnode is mounted on, then we transparently indirect
         * to the vnode which is the root of the mounted file system.
         * Before we do this we must check that an unmount is not in
         * progress on this vnode.
         */

        for (;;) {
                /*
                 * Try to read lock the vnode.  If this fails because
                 * the vnode is already write locked, then check to
                 * see whether it is the current thread which locked
                 * the vnode.  If it is not, then read lock the vnode
                 * by waiting to acquire the lock.
                 *
                 * The code path in domount() is an example of support
                 * which needs to look up two pathnames and locks one
                 * of them in between the two lookups.
                 */
                error = vn_vfsrlock(cvp);
                if (error) {
                        if (!vn_vfswlock_held(cvp))
                                error = vn_vfsrlock_wait(cvp);
                        if (error != 0) {
                                /*
                                 * lookuppn() expects a held vnode to be
                                 * returned because it promptly calls
                                 * VN_RELE after the error return
                                 */
                                *cvpp = cvp;
                                return (error);
                        }
                }

                /*
                 * Reached the end of the mount chain?
                 */
                vfsp = vn_mountedvfs(cvp);
                if (vfsp == NULL) {
                        vn_vfsunlock(cvp);
                        break;
                }

                /*
                 * The read lock must be held across the call to VFS_ROOT() to
                 * prevent a concurrent unmount from destroying the vfs.
                 */
                error = VFS_ROOT(vfsp, &tvp);
                vn_vfsunlock(cvp);

                if (error)
                        break;

                VN_RELE(cvp);

                cvp = tvp;
        }

        *cvpp = cvp;
        return (error);
}

/*
 * Return the lowermost vnode if this is a mountpoint.
 */
static vnode_t *
vn_under(vnode_t *vp)
{
        vnode_t *uvp;
        vfs_t *vfsp;

        while (vp->v_flag & VROOT) {

                vfsp = vp->v_vfsp;
                vfs_rlock_wait(vfsp);
                if ((uvp = vfsp->vfs_vnodecovered) == NULL ||
                    (vfsp->vfs_flag & VFS_UNMOUNTED)) {
                        vfs_unlock(vfsp);
                        break;
                }
                VN_HOLD(uvp);
                vfs_unlock(vfsp);
                VN_RELE(vp);
                vp = uvp;
        }

        return (vp);
}

static int
vnode_match(vnode_t *v1, vnode_t *v2, cred_t *cr)
{
        vattr_t v1attr, v2attr;

        /*
         * If we have a device file, check to see if is a cloned open of the
         * same device.  For self-cloning devices, the major numbers will match.
         * For devices cloned through the 'clone' driver, the minor number of
         * the source device will be the same as the major number of the cloned
         * device.
         */
        if ((v1->v_type == VCHR || v1->v_type == VBLK) &&
            v1->v_type == v2->v_type) {
                if ((spec_is_selfclone(v1) || spec_is_selfclone(v2)) &&
                    getmajor(v1->v_rdev) == getmajor(v2->v_rdev))
                        return (1);

                if (spec_is_clone(v1) &&
                    getmajor(v1->v_rdev) == getminor(v2->v_rdev))
                        return (1);

                if (spec_is_clone(v2) &&
                    getmajor(v2->v_rdev) == getminor(v1->v_rdev))
                        return (1);
        }

        v1attr.va_mask = v2attr.va_mask = AT_TYPE;

        /*
         * This check for symbolic links handles the pseudo-symlinks in procfs.
         * These particular links have v_type of VDIR, but the attributes have a
         * type of VLNK.  We need to avoid these links because otherwise if we
         * are currently in '/proc/self/fd', then '/proc/self/cwd' will compare
         * as the same vnode.
         */
        if (VOP_GETATTR(v1, &v1attr, 0, cr, NULL) != 0 ||
            VOP_GETATTR(v2, &v2attr, 0, cr, NULL) != 0 ||
            v1attr.va_type == VLNK || v2attr.va_type == VLNK)
                return (0);

        v1attr.va_mask = v2attr.va_mask = AT_TYPE | AT_FSID | AT_NODEID;

        if (VOP_GETATTR(v1, &v1attr, ATTR_REAL, cr, NULL) != 0 ||
            VOP_GETATTR(v2, &v2attr, ATTR_REAL, cr, NULL) != 0)
                return (0);

        return (v1attr.va_fsid == v2attr.va_fsid &&
            v1attr.va_nodeid == v2attr.va_nodeid);
}


/*
 * Find the entry in the directory corresponding to the target vnode.
 */
int
dirfindvp(vnode_t *vrootp, vnode_t *dvp, vnode_t *tvp, cred_t *cr, char *dbuf,
    size_t dlen, dirent64_t **rdp)
{
        size_t dbuflen;
        struct iovec iov;
        struct uio uio;
        int error;
        int eof;
        vnode_t *cmpvp;
        struct dirent64 *dp;
        pathname_t pnp;

        ASSERT(dvp->v_type == VDIR);

        /*
         * This is necessary because of the strange semantics of VOP_LOOKUP().
         */
        bzero(&pnp, sizeof (pnp));

        eof = 0;

        uio.uio_iov = &iov;
        uio.uio_iovcnt = 1;
        uio.uio_segflg = UIO_SYSSPACE;
        uio.uio_fmode = 0;
        uio.uio_extflg = UIO_COPY_CACHED;
        uio.uio_loffset = 0;

        if ((error = VOP_ACCESS(dvp, VREAD, 0, cr, NULL)) != 0)
                return (error);

        while (!eof) {
                uio.uio_resid = dlen;
                iov.iov_base = dbuf;
                iov.iov_len = dlen;

                (void) VOP_RWLOCK(dvp, V_WRITELOCK_FALSE, NULL);
                error = VOP_READDIR(dvp, &uio, cr, &eof, NULL, 0);
                VOP_RWUNLOCK(dvp, V_WRITELOCK_FALSE, NULL);

                dbuflen = dlen - uio.uio_resid;

                if (error || dbuflen == 0)
                        break;

                dp = (dirent64_t *)dbuf;
                while ((intptr_t)dp < (intptr_t)dbuf + dbuflen) {
                        /*
                         * Ignore '.' and '..' entries
                         */
                        if (strcmp(dp->d_name, ".") == 0 ||
                            strcmp(dp->d_name, "..") == 0) {
                                dp = (dirent64_t *)((intptr_t)dp +
                                    dp->d_reclen);
                                continue;
                        }

                        error = VOP_LOOKUP(dvp, dp->d_name, &cmpvp, &pnp, 0,
                            vrootp, cr, NULL, NULL, NULL);

                        /*
                         * We only want to bail out if there was an error other
                         * than ENOENT.  Otherwise, it could be that someone
                         * just removed an entry since the readdir() call, and
                         * the entry we want is further on in the directory.
                         */
                        if (error == 0) {
                                if (vnode_match(tvp, cmpvp, cr)) {
                                        VN_RELE(cmpvp);
                                        *rdp = dp;
                                        return (0);
                                }

                                VN_RELE(cmpvp);
                        } else if (error != ENOENT) {
                                return (error);
                        }

                        dp = (dirent64_t *)((intptr_t)dp + dp->d_reclen);
                }
        }

        /*
         * Something strange has happened, this directory does not contain the
         * specified vnode.  This should never happen in the normal case, since
         * we ensured that dvp is the parent of vp.  This is possible in some
         * rare conditions (races and the special .zfs directory).
         */
        if (error == 0) {
                error = VOP_LOOKUP(dvp, ".zfs", &cmpvp, &pnp, 0, vrootp, cr,
                    NULL, NULL, NULL);
                if (error == 0) {
                        if (vnode_match(tvp, cmpvp, cr)) {
                                (void) strcpy(dp->d_name, ".zfs");
                                dp->d_reclen = strlen(".zfs");
                                dp->d_off = 2;
                                dp->d_ino = 1;
                                *rdp = dp;
                        } else {
                                error = ENOENT;
                        }
                        VN_RELE(cmpvp);
                }
        }

        return (error);
}

/*
 * Given a global path (from rootdir), and a vnode that is the current root,
 * return the portion of the path that is beneath the current root or NULL on
 * failure.  The path MUST be a resolved path (no '..' entries or symlinks),
 * otherwise this function will fail.
 */
static char *
localpath(char *path, struct vnode *vrootp, cred_t *cr)
{
        vnode_t *vp;
        vnode_t *cvp;
        char component[MAXNAMELEN];
        char *ret = NULL;
        pathname_t pn;

        /*
         * We use vn_compare() instead of VN_CMP() in order to detect lofs
         * mounts and stacked vnodes.
         */
        if (vn_compare(vrootp, rootdir))
                return (path);

        if (pn_get(path, UIO_SYSSPACE, &pn) != 0)
                return (NULL);

        vp = rootdir;
        VN_HOLD(vp);

        if (vn_ismntpt(vp) && traverse(&vp) != 0) {
                VN_RELE(vp);
                pn_free(&pn);
                return (NULL);
        }

        while (pn_pathleft(&pn)) {
                pn_skipslash(&pn);

                if (pn_getcomponent(&pn, component) != 0)
                        break;

                if (VOP_LOOKUP(vp, component, &cvp, &pn, 0, rootdir, cr,
                    NULL, NULL, NULL) != 0)
                        break;
                VN_RELE(vp);
                vp = cvp;

                if (vn_ismntpt(vp) && traverse(&vp) != 0)
                        break;

                if (vn_compare(vp, vrootp)) {
                        ret = path + (pn.pn_path - pn.pn_buf);
                        break;
                }
        }

        VN_RELE(vp);
        pn_free(&pn);

        return (ret);
}

/*
 * Given a directory, return the full, resolved path.  This looks up "..",
 * searches for the given vnode in the parent, appends the component, etc.  It
 * is used to implement vnodetopath() and getcwd() when the cached path fails.
 */
static int
dirtopath(vnode_t *vrootp, vnode_t *vp, char *buf, size_t buflen, int flags,
    cred_t *cr)
{
        pathname_t pn, rpn, emptypn;
        vnode_t *cmpvp, *pvp = NULL;
        vnode_t *startvp = vp;
        int err = 0, vprivs;
        size_t complen;
        char *dbuf;
        dirent64_t *dp;
        char            *bufloc;
        size_t          dlen = DIRENT64_RECLEN(MAXPATHLEN);
        refstr_t        *mntpt;

        /* Operation only allowed on directories */
        ASSERT(vp->v_type == VDIR);

        /* We must have at least enough space for "/" */
        if (buflen < 2)
                return (ENAMETOOLONG);

        /* Start at end of string with terminating null */
        bufloc = &buf[buflen - 1];
        *bufloc = '\0';

        pn_alloc(&pn);
        pn_alloc(&rpn);
        dbuf = kmem_alloc(dlen, KM_SLEEP);
        bzero(&emptypn, sizeof (emptypn));

        /*
         * Begin with an additional reference on vp.  This will be decremented
         * during the loop.
         */
        VN_HOLD(vp);

        for (;;) {
                /*
                 * Return if we've reached the root.  If the buffer is empty,
                 * return '/'.  We explicitly don't use vn_compare(), since it
                 * compares the real vnodes.  A lofs mount of '/' would produce
                 * incorrect results otherwise.
                 */
                if (VN_CMP(vrootp, vp)) {
                        if (*bufloc == '\0')
                                *--bufloc = '/';
                        break;
                }

                /*
                 * If we've reached the VFS root, something has gone wrong.  We
                 * should have reached the root in the above check.  The only
                 * explantation is that 'vp' is not contained withing the given
                 * root, in which case we return EPERM.
                 */
                if (VN_CMP(rootdir, vp)) {
                        err = EPERM;
                        goto out;
                }

                /*
                 * Shortcut: see if this vnode is a mountpoint.  If so,
                 * grab the path information from the vfs_t.
                 */
                if (vp->v_flag & VROOT) {

                        mntpt = vfs_getmntpoint(vp->v_vfsp);
                        if ((err = pn_set(&pn, (char *)refstr_value(mntpt)))
                            == 0) {
                                refstr_rele(mntpt);
                                rpn.pn_path = rpn.pn_buf;

                                /*
                                 * Ensure the mountpoint still exists.
                                 */
                                VN_HOLD(vrootp);
                                if (vrootp != rootdir)
                                        VN_HOLD(vrootp);
                                if (lookuppnvp(&pn, &rpn, flags, NULL,
                                    &cmpvp, vrootp, vrootp, cr) == 0) {

                                        if (VN_CMP(vp, cmpvp)) {
                                                VN_RELE(cmpvp);

                                                complen = strlen(rpn.pn_path);
                                                bufloc -= complen;
                                                if (bufloc < buf) {
                                                        err = ERANGE;
                                                        goto out;
                                                }
                                                bcopy(rpn.pn_path, bufloc,
                                                    complen);
                                                break;
                                        } else {
                                                VN_RELE(cmpvp);
                                        }
                                }
                        } else {
                                refstr_rele(mntpt);
                        }
                }

                /*
                 * Shortcut: see if this vnode has correct v_path. If so,
                 * we have the work done.
                 */
                mutex_enter(&vp->v_lock);
                if (vp->v_path != NULL) {

                        if ((err = pn_set(&pn, vp->v_path)) == 0) {
                                mutex_exit(&vp->v_lock);
                                rpn.pn_path = rpn.pn_buf;

                                /*
                                 * Ensure the v_path pointing to correct vnode
                                 */
                                VN_HOLD(vrootp);
                                if (vrootp != rootdir)
                                        VN_HOLD(vrootp);
                                if (lookuppnvp(&pn, &rpn, flags, NULL,
                                    &cmpvp, vrootp, vrootp, cr) == 0) {

                                        if (VN_CMP(vp, cmpvp)) {
                                                VN_RELE(cmpvp);

                                                complen = strlen(rpn.pn_path);
                                                bufloc -= complen;
                                                if (bufloc < buf) {
                                                        err = ERANGE;
                                                        goto out;
                                                }
                                                bcopy(rpn.pn_path, bufloc,
                                                    complen);
                                                break;
                                        } else {
                                                VN_RELE(cmpvp);
                                        }
                                }
                        } else {
                                mutex_exit(&vp->v_lock);
                        }
                } else {
                        mutex_exit(&vp->v_lock);
                }

                /*
                 * Shortcuts failed, search for this vnode in its parent.  If
                 * this is a mountpoint, then get the vnode underneath.
                 */
                if (vp->v_flag & VROOT)
                        vp = vn_under(vp);
                if ((err = VOP_LOOKUP(vp, "..", &pvp, &emptypn, 0, vrootp, cr,
                    NULL, NULL, NULL)) != 0)
                        goto out;

                /*
                 * With extended attributes, it's possible for a directory to
                 * have a parent that is a regular file.  Check for that here.
                 */
                if (pvp->v_type != VDIR) {
                        err = ENOTDIR;
                        goto out;
                }

                /*
                 * If this is true, something strange has happened.  This is
                 * only true if we are the root of a filesystem, which should
                 * have been caught by the check above.
                 */
                if (VN_CMP(pvp, vp)) {
                        err = ENOENT;
                        goto out;
                }

                /*
                 * Check if we have read and search privilege so, that
                 * we can lookup the path in the directory
                 */
                vprivs = (flags & LOOKUP_CHECKREAD) ? VREAD | VEXEC : VEXEC;
                if ((err = VOP_ACCESS(pvp, vprivs, 0, cr, NULL)) != 0) {
                        goto out;
                }

                /*
                 * Try to obtain the path component from dnlc cache
                 * before searching through the directory.
                 */
                if ((cmpvp = dnlc_reverse_lookup(vp, dbuf, dlen)) != NULL) {
                        /*
                         * If we got parent vnode as a result,
                         * then the answered path is correct.
                         */
                        if (VN_CMP(cmpvp, pvp)) {
                                VN_RELE(cmpvp);
                                complen = strlen(dbuf);
                                bufloc -= complen;
                                if (bufloc <= buf) {
                                        err = ENAMETOOLONG;
                                        goto out;
                                }
                                bcopy(dbuf, bufloc, complen);

                                /* Prepend a slash to the current path */
                                *--bufloc = '/';

                                /* And continue with the next component */
                                VN_RELE(vp);
                                vp = pvp;
                                pvp = NULL;
                                continue;
                        } else {
                                VN_RELE(cmpvp);
                        }
                }

                /*
                 * Search the parent directory for the entry corresponding to
                 * this vnode.
                 */
                if ((err = dirfindvp(vrootp, pvp, vp, cr, dbuf, dlen, &dp))
                    != 0)
                        goto out;
                complen = strlen(dp->d_name);
                bufloc -= complen;
                if (bufloc <= buf) {
                        err = ENAMETOOLONG;
                        goto out;
                }
                bcopy(dp->d_name, bufloc, complen);

                /* Prepend a slash to the current path.  */
                *--bufloc = '/';

                /* And continue with the next component */
                VN_RELE(vp);
                vp = pvp;
                pvp = NULL;
        }

        /*
         * Place the path at the beginning of the buffer.
         */
        if (bufloc != buf)
                ovbcopy(bufloc, buf, buflen - (bufloc - buf));

out:
        /*
         * If the error was ESTALE and the current directory to look in
         * was the root for this lookup, the root for a mounted file
         * system, or the starting directory for lookups, then
         * return ENOENT instead of ESTALE.  In this case, no recovery
         * is possible by the higher level.  If ESTALE was returned for
         * some intermediate directory along the path, then recovery
         * is potentially possible and retrying from the higher level
         * will either correct the situation by purging stale cache
         * entries or eventually get back to the point where no recovery
         * is possible.
         */
        if (err == ESTALE &&
            (VN_CMP(vp, vrootp) || (vp->v_flag & VROOT) || vp == startvp))
                err = ENOENT;

        kmem_free(dbuf, dlen);
        VN_RELE(vp);
        if (pvp)
                VN_RELE(pvp);
        pn_free(&pn);
        pn_free(&rpn);

        return (err);
}

/*
 * The additional flag, LOOKUP_CHECKREAD, is used to enforce artificial
 * constraints in order to be standards compliant.  For example, if we have
 * the cached path of '/foo/bar', and '/foo' has permissions 100 (execute
 * only), then we can legitimately look up the path to the current working
 * directory without needing read permission.  Existing standards tests,
 * however, assume that we are determining the path by repeatedly looking up
 * "..".  We need to keep this behavior in order to maintain backwards
 * compatibility.
 */
static int
vnodetopath_common(vnode_t *vrootp, vnode_t *vp, char *buf, size_t buflen,
    cred_t *cr, int flags)
{
        pathname_t pn, rpn;
        int ret, len;
        vnode_t *compvp, *pvp, *realvp;
        proc_t *p = curproc;
        char path[MAXNAMELEN];
        int doclose = 0;

        /*
         * If vrootp is NULL, get the root for curproc.  Callers with any other
         * requirements should pass in a different vrootp.
         */
        if (vrootp == NULL) {
                mutex_enter(&p->p_lock);
                if ((vrootp = PTOU(p)->u_rdir) == NULL)
                        vrootp = rootdir;
                VN_HOLD(vrootp);
                mutex_exit(&p->p_lock);
        } else {
                VN_HOLD(vrootp);
        }

        /*
         * This is to get around an annoying artifact of the /proc filesystem,
         * which is the behavior of {cwd/root}.  Trying to resolve this path
         * will result in /proc/pid/cwd instead of whatever the real working
         * directory is.  We can't rely on VOP_REALVP(), since that will break
         * lofs.  The only difference between procfs and lofs is that opening
         * the file will return the underling vnode in the case of procfs.
         */
        if (vp->v_type == VDIR && VOP_REALVP(vp, &realvp, NULL) == 0 &&
            realvp != vp) {
                VN_HOLD(vp);
                if (VOP_OPEN(&vp, FREAD, cr, NULL) == 0)
                        doclose = 1;
                else
                        VN_RELE(vp);
        }

        pn_alloc(&pn);

        /*
         * Check to see if we have a cached path in the vnode.
         */
        mutex_enter(&vp->v_lock);
        if (vp->v_path != NULL) {
                (void) pn_set(&pn, vp->v_path);
                mutex_exit(&vp->v_lock);

                pn_alloc(&rpn);

                /* We should only cache absolute paths */
                ASSERT(pn.pn_buf[0] == '/');

                /*
                 * If we are in a zone or a chroot environment, then we have to
                 * take additional steps, since the path to the root might not
                 * be readable with the current credentials, even though the
                 * process can legitmately access the file.  In this case, we
                 * do the following:
                 *
                 * lookuppnvp() with all privileges to get the resolved path.
                 * call localpath() to get the local portion of the path, and
                 * continue as normal.
                 *
                 * If the the conversion to a local path fails, then we continue
                 * as normal.  This is a heuristic to make process object file
                 * paths available from within a zone.  Because lofs doesn't
                 * support page operations, the vnode stored in the seg_t is
                 * actually the underlying real vnode, not the lofs node itself.
                 * Most of the time, the lofs path is the same as the underlying
                 * vnode (for example, /usr/lib/libc.so.1).
                 */
                if (vrootp != rootdir) {
                        char *local = NULL;
                        VN_HOLD(rootdir);
                        if (lookuppnvp(&pn, &rpn, FOLLOW,
                            NULL, &compvp, rootdir, rootdir, kcred) == 0) {
                                local = localpath(rpn.pn_path, vrootp,
                                    kcred);
                                VN_RELE(compvp);
                        }

                        /*
                         * The original pn was changed through lookuppnvp().
                         * Set it to local for next validation attempt.
                         */
                        if (local) {
                                (void) pn_set(&pn, local);
                        } else {
                                goto notcached;
                        }
                }

                /*
                 * We should have a local path at this point, so start the
                 * search from the root of the current process.
                 */
                VN_HOLD(vrootp);
                if (vrootp != rootdir)
                        VN_HOLD(vrootp);
                ret = lookuppnvp(&pn, &rpn, FOLLOW | flags, NULL,
                    &compvp, vrootp, vrootp, cr);
                if (ret == 0) {
                        /*
                         * Check to see if the returned vnode is the same as
                         * the one we expect.  If not, give up.
                         */
                        if (!vn_compare(vp, compvp) &&
                            !vnode_match(vp, compvp, cr)) {
                                VN_RELE(compvp);
                                goto notcached;
                        }

                        VN_RELE(compvp);

                        /*
                         * Return the result.
                         */
                        if (buflen <= rpn.pn_pathlen)
                                goto notcached;

                        bcopy(rpn.pn_path, buf, rpn.pn_pathlen + 1);
                        pn_free(&pn);
                        pn_free(&rpn);
                        VN_RELE(vrootp);
                        if (doclose) {
                                (void) VOP_CLOSE(vp, FREAD, 1, 0, cr, NULL);
                                VN_RELE(vp);
                        }
                        return (0);
                }

notcached:
                pn_free(&rpn);
        } else {
                mutex_exit(&vp->v_lock);
        }

        pn_free(&pn);

        if (vp->v_type != VDIR) {
                /*
                 * If we don't have a directory, try to find it in the dnlc via
                 * reverse lookup.  Once this is found, we can use the regular
                 * directory search to find the full path.
                 */
                if ((pvp = dnlc_reverse_lookup(vp, path, MAXNAMELEN)) != NULL) {
                        /*
                         * Check if we have read privilege so, that
                         * we can lookup the path in the directory
                         */
                        ret = 0;
                        if ((flags & LOOKUP_CHECKREAD)) {
                                ret = VOP_ACCESS(pvp, VREAD, 0, cr, NULL);
                        }
                        if (ret == 0) {
                                ret = dirtopath(vrootp, pvp, buf, buflen,
                                    flags, cr);
                        }
                        if (ret == 0) {
                                len = strlen(buf);
                                if (len + strlen(path) + 1 >= buflen) {
                                        ret = ENAMETOOLONG;
                                } else {
                                        if (buf[len - 1] != '/')
                                                buf[len++] = '/';
                                        bcopy(path, buf + len,
                                            strlen(path) + 1);
                                }
                        }

                        VN_RELE(pvp);
                } else
                        ret = ENOENT;
        } else
                ret = dirtopath(vrootp, vp, buf, buflen, flags, cr);

        VN_RELE(vrootp);
        if (doclose) {
                (void) VOP_CLOSE(vp, FREAD, 1, 0, cr, NULL);
                VN_RELE(vp);
        }

        return (ret);
}

int
vnodetopath(vnode_t *vrootp, vnode_t *vp, char *buf, size_t buflen, cred_t *cr)
{
        return (vnodetopath_common(vrootp, vp, buf, buflen, cr, 0));
}

int
dogetcwd(char *buf, size_t buflen)
{
        int ret;
        vnode_t *vp;
        vnode_t *compvp;
        refstr_t *cwd, *oldcwd;
        const char *value;
        pathname_t rpnp, pnp;
        proc_t *p = curproc;

        /*
         * Check to see if there is a cached version of the cwd.  If so, lookup
         * the cached value and make sure it is the same vnode.
         */
        mutex_enter(&p->p_lock);
        if ((cwd = PTOU(p)->u_cwd) != NULL)
                refstr_hold(cwd);
        vp = PTOU(p)->u_cdir;
        VN_HOLD(vp);
        mutex_exit(&p->p_lock);

        /*
         * Make sure we have permission to access the current directory.
         */
        if ((ret = VOP_ACCESS(vp, VEXEC, 0, CRED(), NULL)) != 0) {
                if (cwd != NULL)
                        refstr_rele(cwd);
                VN_RELE(vp);
                return (ret);
        }

        if (cwd) {
                value = refstr_value(cwd);
                if ((ret = pn_get((char *)value, UIO_SYSSPACE, &pnp)) != 0) {
                        refstr_rele(cwd);
                        VN_RELE(vp);
                        return (ret);
                }

                pn_alloc(&rpnp);

                if (lookuppn(&pnp, &rpnp, NO_FOLLOW, NULL, &compvp) == 0) {

                        if (VN_CMP(vp, compvp) &&
                            strcmp(value, rpnp.pn_path) == 0) {
                                VN_RELE(compvp);
                                VN_RELE(vp);
                                pn_free(&pnp);
                                pn_free(&rpnp);
                                if (strlen(value) + 1 > buflen) {
                                        refstr_rele(cwd);
                                        return (ENAMETOOLONG);
                                }
                                bcopy(value, buf, strlen(value) + 1);
                                refstr_rele(cwd);
                                return (0);
                        }

                        VN_RELE(compvp);
                }

                pn_free(&rpnp);
                pn_free(&pnp);

                refstr_rele(cwd);
        }

        ret = vnodetopath_common(NULL, vp, buf, buflen, CRED(),
            LOOKUP_CHECKREAD);

        VN_RELE(vp);

        /*
         * Store the new cwd and replace the existing cached copy.
         */
        if (ret == 0)
                cwd = refstr_alloc(buf);
        else
                cwd = NULL;

        mutex_enter(&p->p_lock);
        oldcwd = PTOU(p)->u_cwd;
        PTOU(p)->u_cwd = cwd;
        mutex_exit(&p->p_lock);

        if (oldcwd)
                refstr_rele(oldcwd);

        return (ret);
}