Fix O_APPEND for Linux 3.15 and older kernels

[zfs.git] / module / os / linux / zfs / zpl_xattr.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) 2011, Lawrence Livermore National Security, LLC.
 *
 * Extended attributes (xattr) on Solaris are implemented as files
 * which exist in a hidden xattr directory.  These extended attributes
 * can be accessed using the attropen() system call which opens
 * the extended attribute.  It can then be manipulated just like
 * a standard file descriptor.  This has a couple advantages such
 * as practically no size limit on the file, and the extended
 * attributes permissions may differ from those of the parent file.
 * This interface is really quite clever, but it's also completely
 * different than what is supported on Linux.  It also comes with a
 * steep performance penalty when accessing small xattrs because they
 * are not stored with the parent file.
 *
 * Under Linux extended attributes are manipulated by the system
 * calls getxattr(2), setxattr(2), and listxattr(2).  They consider
 * extended attributes to be name/value pairs where the name is a
 * NULL terminated string.  The name must also include one of the
 * following namespace prefixes:
 *
 *   user     - No restrictions and is available to user applications.
 *   trusted  - Restricted to kernel and root (CAP_SYS_ADMIN) use.
 *   system   - Used for access control lists (system.nfs4_acl, etc).
 *   security - Used by SELinux to store a files security context.
 *
 * The value under Linux to limited to 65536 bytes of binary data.
 * In practice, individual xattrs tend to be much smaller than this
 * and are typically less than 100 bytes.  A good example of this
 * are the security.selinux xattrs which are less than 100 bytes and
 * exist for every file when xattr labeling is enabled.
 *
 * The Linux xattr implementation has been written to take advantage of
 * this typical usage.  When the dataset property 'xattr=sa' is set,
 * then xattrs will be preferentially stored as System Attributes (SA).
 * This allows tiny xattrs (~100 bytes) to be stored with the dnode and
 * up to 64k of xattrs to be stored in the spill block.  If additional
 * xattr space is required, which is unlikely under Linux, they will
 * be stored using the traditional directory approach.
 *
 * This optimization results in roughly a 3x performance improvement
 * when accessing xattrs because it avoids the need to perform a seek
 * for every xattr value.  When multiple xattrs are stored per-file
 * the performance improvements are even greater because all of the
 * xattrs stored in the spill block will be cached.
 *
 * However, by default SA based xattrs are disabled in the Linux port
 * to maximize compatibility with other implementations.  If you do
 * enable SA based xattrs then they will not be visible on platforms
 * which do not support this feature.
 *
 * NOTE: One additional consequence of the xattr directory implementation
 * is that when an extended attribute is manipulated an inode is created.
 * This inode will exist in the Linux inode cache but there will be no
 * associated entry in the dentry cache which references it.  This is
 * safe but it may result in some confusion.  Enabling SA based xattrs
 * largely avoids the issue except in the overflow case.
 */

#include <sys/zfs_znode.h>
#include <sys/zfs_vfsops.h>
#include <sys/zfs_vnops.h>
#include <sys/zap.h>
#include <sys/vfs.h>
#include <sys/zpl.h>

enum xattr_permission {
        XAPERM_DENY,
        XAPERM_ALLOW,
        XAPERM_COMPAT,
};

typedef struct xattr_filldir {
        size_t size;
        size_t offset;
        char *buf;
        struct dentry *dentry;
} xattr_filldir_t;

static enum xattr_permission zpl_xattr_permission(xattr_filldir_t *,
    const char *, int);

static int zfs_xattr_compat = 0;

/*
 * Determine is a given xattr name should be visible and if so copy it
 * in to the provided buffer (xf->buf).
 */
static int
zpl_xattr_filldir(xattr_filldir_t *xf, const char *name, int name_len)
{
        enum xattr_permission perm;

        /* Check permissions using the per-namespace list xattr handler. */
        perm = zpl_xattr_permission(xf, name, name_len);
        if (perm == XAPERM_DENY)
                return (0);

        /* Prefix the name with "user." if it does not have a namespace. */
        if (perm == XAPERM_COMPAT) {
                if (xf->buf) {
                        if (xf->offset + XATTR_USER_PREFIX_LEN + 1 > xf->size)
                                return (-ERANGE);

                        memcpy(xf->buf + xf->offset, XATTR_USER_PREFIX,
                            XATTR_USER_PREFIX_LEN);
                        xf->buf[xf->offset + XATTR_USER_PREFIX_LEN] = '\0';
                }

                xf->offset += XATTR_USER_PREFIX_LEN;
        }

        /* When xf->buf is NULL only calculate the required size. */
        if (xf->buf) {
                if (xf->offset + name_len + 1 > xf->size)
                        return (-ERANGE);

                memcpy(xf->buf + xf->offset, name, name_len);
                xf->buf[xf->offset + name_len] = '\0';
        }

        xf->offset += (name_len + 1);

        return (0);
}

/*
 * Read as many directory entry names as will fit in to the provided buffer,
 * or when no buffer is provided calculate the required buffer size.
 */
static int
zpl_xattr_readdir(struct inode *dxip, xattr_filldir_t *xf)
{
        zap_cursor_t zc;
        zap_attribute_t zap;
        int error;

        zap_cursor_init(&zc, ITOZSB(dxip)->z_os, ITOZ(dxip)->z_id);

        while ((error = -zap_cursor_retrieve(&zc, &zap)) == 0) {

                if (zap.za_integer_length != 8 || zap.za_num_integers != 1) {
                        error = -ENXIO;
                        break;
                }

                error = zpl_xattr_filldir(xf, zap.za_name, strlen(zap.za_name));
                if (error)
                        break;

                zap_cursor_advance(&zc);
        }

        zap_cursor_fini(&zc);

        if (error == -ENOENT)
                error = 0;

        return (error);
}

static ssize_t
zpl_xattr_list_dir(xattr_filldir_t *xf, cred_t *cr)
{
        struct inode *ip = xf->dentry->d_inode;
        struct inode *dxip = NULL;
        znode_t *dxzp;
        int error;

        /* Lookup the xattr directory */
        error = -zfs_lookup(ITOZ(ip), NULL, &dxzp, LOOKUP_XATTR,
            cr, NULL, NULL);
        if (error) {
                if (error == -ENOENT)
                        error = 0;

                return (error);
        }

        dxip = ZTOI(dxzp);
        error = zpl_xattr_readdir(dxip, xf);
        iput(dxip);

        return (error);
}

static ssize_t
zpl_xattr_list_sa(xattr_filldir_t *xf)
{
        znode_t *zp = ITOZ(xf->dentry->d_inode);
        nvpair_t *nvp = NULL;
        int error = 0;

        mutex_enter(&zp->z_lock);
        if (zp->z_xattr_cached == NULL)
                error = -zfs_sa_get_xattr(zp);
        mutex_exit(&zp->z_lock);

        if (error)
                return (error);

        ASSERT(zp->z_xattr_cached);

        while ((nvp = nvlist_next_nvpair(zp->z_xattr_cached, nvp)) != NULL) {
                ASSERT3U(nvpair_type(nvp), ==, DATA_TYPE_BYTE_ARRAY);

                error = zpl_xattr_filldir(xf, nvpair_name(nvp),
                    strlen(nvpair_name(nvp)));
                if (error)
                        return (error);
        }

        return (0);
}

ssize_t
zpl_xattr_list(struct dentry *dentry, char *buffer, size_t buffer_size)
{
        znode_t *zp = ITOZ(dentry->d_inode);
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        xattr_filldir_t xf = { buffer_size, 0, buffer, dentry };
        cred_t *cr = CRED();
        fstrans_cookie_t cookie;
        int error = 0;

        crhold(cr);
        cookie = spl_fstrans_mark();
        ZPL_ENTER(zfsvfs);
        ZPL_VERIFY_ZP(zp);
        rw_enter(&zp->z_xattr_lock, RW_READER);

        if (zfsvfs->z_use_sa && zp->z_is_sa) {
                error = zpl_xattr_list_sa(&xf);
                if (error)
                        goto out;
        }

        error = zpl_xattr_list_dir(&xf, cr);
        if (error)
                goto out;

        error = xf.offset;
out:

        rw_exit(&zp->z_xattr_lock);
        ZPL_EXIT(zfsvfs);
        spl_fstrans_unmark(cookie);
        crfree(cr);

        return (error);
}

static int
zpl_xattr_get_dir(struct inode *ip, const char *name, void *value,
    size_t size, cred_t *cr)
{
        fstrans_cookie_t cookie;
        struct inode *xip = NULL;
        znode_t *dxzp = NULL;
        znode_t *xzp = NULL;
        int error;

        /* Lookup the xattr directory */
        error = -zfs_lookup(ITOZ(ip), NULL, &dxzp, LOOKUP_XATTR,
            cr, NULL, NULL);
        if (error)
                goto out;

        /* Lookup a specific xattr name in the directory */
        error = -zfs_lookup(dxzp, (char *)name, &xzp, 0, cr, NULL, NULL);
        if (error)
                goto out;

        xip = ZTOI(xzp);
        if (!size) {
                error = i_size_read(xip);
                goto out;
        }

        if (size < i_size_read(xip)) {
                error = -ERANGE;
                goto out;
        }

        struct iovec iov;
        iov.iov_base = (void *)value;
        iov.iov_len = size;

        zfs_uio_t uio;
        zfs_uio_iovec_init(&uio, &iov, 1, 0, UIO_SYSSPACE, size, 0);

        cookie = spl_fstrans_mark();
        error = -zfs_read(ITOZ(xip), &uio, 0, cr);
        spl_fstrans_unmark(cookie);

        if (error == 0)
                error = size - zfs_uio_resid(&uio);
out:
        if (xzp)
                zrele(xzp);

        if (dxzp)
                zrele(dxzp);

        return (error);
}

static int
zpl_xattr_get_sa(struct inode *ip, const char *name, void *value, size_t size)
{
        znode_t *zp = ITOZ(ip);
        uchar_t *nv_value;
        uint_t nv_size;
        int error = 0;

        ASSERT(RW_LOCK_HELD(&zp->z_xattr_lock));

        mutex_enter(&zp->z_lock);
        if (zp->z_xattr_cached == NULL)
                error = -zfs_sa_get_xattr(zp);
        mutex_exit(&zp->z_lock);

        if (error)
                return (error);

        ASSERT(zp->z_xattr_cached);
        error = -nvlist_lookup_byte_array(zp->z_xattr_cached, name,
            &nv_value, &nv_size);
        if (error)
                return (error);

        if (size == 0 || value == NULL)
                return (nv_size);

        if (size < nv_size)
                return (-ERANGE);

        memcpy(value, nv_value, nv_size);

        return (nv_size);
}

static int
__zpl_xattr_get(struct inode *ip, const char *name, void *value, size_t size,
    cred_t *cr)
{
        znode_t *zp = ITOZ(ip);
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        int error;

        ASSERT(RW_LOCK_HELD(&zp->z_xattr_lock));

        if (zfsvfs->z_use_sa && zp->z_is_sa) {
                error = zpl_xattr_get_sa(ip, name, value, size);
                if (error != -ENOENT)
                        goto out;
        }

        error = zpl_xattr_get_dir(ip, name, value, size, cr);
out:
        if (error == -ENOENT)
                error = -ENODATA;

        return (error);
}

#define XATTR_NOENT     0x0
#define XATTR_IN_SA     0x1
#define XATTR_IN_DIR    0x2
/* check where the xattr resides */
static int
__zpl_xattr_where(struct inode *ip, const char *name, int *where, cred_t *cr)
{
        znode_t *zp = ITOZ(ip);
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        int error;

        ASSERT(where);
        ASSERT(RW_LOCK_HELD(&zp->z_xattr_lock));

        *where = XATTR_NOENT;
        if (zfsvfs->z_use_sa && zp->z_is_sa) {
                error = zpl_xattr_get_sa(ip, name, NULL, 0);
                if (error >= 0)
                        *where |= XATTR_IN_SA;
                else if (error != -ENOENT)
                        return (error);
        }

        error = zpl_xattr_get_dir(ip, name, NULL, 0, cr);
        if (error >= 0)
                *where |= XATTR_IN_DIR;
        else if (error != -ENOENT)
                return (error);

        if (*where == (XATTR_IN_SA|XATTR_IN_DIR))
                cmn_err(CE_WARN, "ZFS: inode %p has xattr \"%s\""
                    " in both SA and dir", ip, name);
        if (*where == XATTR_NOENT)
                error = -ENODATA;
        else
                error = 0;
        return (error);
}

static int
zpl_xattr_get(struct inode *ip, const char *name, void *value, size_t size)
{
        znode_t *zp = ITOZ(ip);
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        cred_t *cr = CRED();
        fstrans_cookie_t cookie;
        int error;

        crhold(cr);
        cookie = spl_fstrans_mark();
        ZPL_ENTER(zfsvfs);
        ZPL_VERIFY_ZP(zp);
        rw_enter(&zp->z_xattr_lock, RW_READER);
        error = __zpl_xattr_get(ip, name, value, size, cr);
        rw_exit(&zp->z_xattr_lock);
        ZPL_EXIT(zfsvfs);
        spl_fstrans_unmark(cookie);
        crfree(cr);

        return (error);
}

static int
zpl_xattr_set_dir(struct inode *ip, const char *name, const void *value,
    size_t size, int flags, cred_t *cr)
{
        znode_t *dxzp = NULL;
        znode_t *xzp = NULL;
        vattr_t *vap = NULL;
        int lookup_flags, error;
        const int xattr_mode = S_IFREG | 0644;
        loff_t pos = 0;

        /*
         * Lookup the xattr directory.  When we're adding an entry pass
         * CREATE_XATTR_DIR to ensure the xattr directory is created.
         * When removing an entry this flag is not passed to avoid
         * unnecessarily creating a new xattr directory.
         */
        lookup_flags = LOOKUP_XATTR;
        if (value != NULL)
                lookup_flags |= CREATE_XATTR_DIR;

        error = -zfs_lookup(ITOZ(ip), NULL, &dxzp, lookup_flags,
            cr, NULL, NULL);
        if (error)
                goto out;

        /* Lookup a specific xattr name in the directory */
        error = -zfs_lookup(dxzp, (char *)name, &xzp, 0, cr, NULL, NULL);
        if (error && (error != -ENOENT))
                goto out;

        error = 0;

        /* Remove a specific name xattr when value is set to NULL. */
        if (value == NULL) {
                if (xzp)
                        error = -zfs_remove(dxzp, (char *)name, cr, 0);

                goto out;
        }

        /* Lookup failed create a new xattr. */
        if (xzp == NULL) {
                vap = kmem_zalloc(sizeof (vattr_t), KM_SLEEP);
                vap->va_mode = xattr_mode;
                vap->va_mask = ATTR_MODE;
                vap->va_uid = crgetuid(cr);
                vap->va_gid = crgetgid(cr);

                error = -zfs_create(dxzp, (char *)name, vap, 0, 0644, &xzp,
                    cr, 0, NULL);
                if (error)
                        goto out;
        }

        ASSERT(xzp != NULL);

        error = -zfs_freesp(xzp, 0, 0, xattr_mode, TRUE);
        if (error)
                goto out;

        error = -zfs_write_simple(xzp, value, size, pos, NULL);
out:
        if (error == 0) {
                ip->i_ctime = current_time(ip);
                zfs_mark_inode_dirty(ip);
        }

        if (vap)
                kmem_free(vap, sizeof (vattr_t));

        if (xzp)
                zrele(xzp);

        if (dxzp)
                zrele(dxzp);

        if (error == -ENOENT)
                error = -ENODATA;

        ASSERT3S(error, <=, 0);

        return (error);
}

static int
zpl_xattr_set_sa(struct inode *ip, const char *name, const void *value,
    size_t size, int flags, cred_t *cr)
{
        znode_t *zp = ITOZ(ip);
        nvlist_t *nvl;
        size_t sa_size;
        int error = 0;

        mutex_enter(&zp->z_lock);
        if (zp->z_xattr_cached == NULL)
                error = -zfs_sa_get_xattr(zp);
        mutex_exit(&zp->z_lock);

        if (error)
                return (error);

        ASSERT(zp->z_xattr_cached);
        nvl = zp->z_xattr_cached;

        if (value == NULL) {
                error = -nvlist_remove(nvl, name, DATA_TYPE_BYTE_ARRAY);
                if (error == -ENOENT)
                        error = zpl_xattr_set_dir(ip, name, NULL, 0, flags, cr);
        } else {
                /* Limited to 32k to keep nvpair memory allocations small */
                if (size > DXATTR_MAX_ENTRY_SIZE)
                        return (-EFBIG);

                /* Prevent the DXATTR SA from consuming the entire SA region */
                error = -nvlist_size(nvl, &sa_size, NV_ENCODE_XDR);
                if (error)
                        return (error);

                if (sa_size > DXATTR_MAX_SA_SIZE)
                        return (-EFBIG);

                error = -nvlist_add_byte_array(nvl, name,
                    (uchar_t *)value, size);
        }

        /*
         * Update the SA for additions, modifications, and removals. On
         * error drop the inconsistent cached version of the nvlist, it
         * will be reconstructed from the ARC when next accessed.
         */
        if (error == 0)
                error = -zfs_sa_set_xattr(zp, name, value, size);

        if (error) {
                nvlist_free(nvl);
                zp->z_xattr_cached = NULL;
        }

        ASSERT3S(error, <=, 0);

        return (error);
}

static int
zpl_xattr_set(struct inode *ip, const char *name, const void *value,
    size_t size, int flags)
{
        znode_t *zp = ITOZ(ip);
        zfsvfs_t *zfsvfs = ZTOZSB(zp);
        cred_t *cr = CRED();
        fstrans_cookie_t cookie;
        int where;
        int error;

        crhold(cr);
        cookie = spl_fstrans_mark();
        ZPL_ENTER(zfsvfs);
        ZPL_VERIFY_ZP(zp);
        rw_enter(&zp->z_xattr_lock, RW_WRITER);

        /*
         * Before setting the xattr check to see if it already exists.
         * This is done to ensure the following optional flags are honored.
         *
         *   XATTR_CREATE: fail if xattr already exists
         *   XATTR_REPLACE: fail if xattr does not exist
         *
         * We also want to know if it resides in sa or dir, so we can make
         * sure we don't end up with duplicate in both places.
         */
        error = __zpl_xattr_where(ip, name, &where, cr);
        if (error < 0) {
                if (error != -ENODATA)
                        goto out;
                if (flags & XATTR_REPLACE)
                        goto out;

                /* The xattr to be removed already doesn't exist */
                error = 0;
                if (value == NULL)
                        goto out;
        } else {
                error = -EEXIST;
                if (flags & XATTR_CREATE)
                        goto out;
        }

        /* Preferentially store the xattr as a SA for better performance */
        if (zfsvfs->z_use_sa && zp->z_is_sa &&
            (zfsvfs->z_xattr_sa || (value == NULL && where & XATTR_IN_SA))) {
                error = zpl_xattr_set_sa(ip, name, value, size, flags, cr);
                if (error == 0) {
                        /*
                         * Successfully put into SA, we need to clear the one
                         * in dir.
                         */
                        if (where & XATTR_IN_DIR)
                                zpl_xattr_set_dir(ip, name, NULL, 0, 0, cr);
                        goto out;
                }
        }

        error = zpl_xattr_set_dir(ip, name, value, size, flags, cr);
        /*
         * Successfully put into dir, we need to clear the one in SA.
         */
        if (error == 0 && (where & XATTR_IN_SA))
                zpl_xattr_set_sa(ip, name, NULL, 0, 0, cr);
out:
        rw_exit(&zp->z_xattr_lock);
        ZPL_EXIT(zfsvfs);
        spl_fstrans_unmark(cookie);
        crfree(cr);
        ASSERT3S(error, <=, 0);

        return (error);
}

/*
 * Extended user attributes
 *
 * "Extended user attributes may be assigned to files and directories for
 * storing arbitrary additional information such as the mime type,
 * character set or encoding of a file.  The access permissions for user
 * attributes are defined by the file permission bits: read permission
 * is required to retrieve the attribute value, and writer permission is
 * required to change it.
 *
 * The file permission bits of regular files and directories are
 * interpreted differently from the file permission bits of special
 * files and symbolic links.  For regular files and directories the file
 * permission bits define access to the file's contents, while for
 * device special files they define access to the device described by
 * the special file.  The file permissions of symbolic links are not
 * used in access checks.  These differences would allow users to
 * consume filesystem resources in a way not controllable by disk quotas
 * for group or world writable special files and directories.
 *
 * For this reason, extended user attributes are allowed only for
 * regular files and directories, and access to extended user attributes
 * is restricted to the owner and to users with appropriate capabilities
 * for directories with the sticky bit set (see the chmod(1) manual page
 * for an explanation of the sticky bit)." - xattr(7)
 *
 * ZFS allows extended user attributes to be disabled administratively
 * by setting the 'xattr=off' property on the dataset.
 */
static int
__zpl_xattr_user_list(struct inode *ip, char *list, size_t list_size,
    const char *name, size_t name_len)
{
        return (ITOZSB(ip)->z_flags & ZSB_XATTR);
}
ZPL_XATTR_LIST_WRAPPER(zpl_xattr_user_list);

static int
__zpl_xattr_user_get(struct inode *ip, const char *name,
    void *value, size_t size)
{
        int error;
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") == 0)
                return (-EINVAL);
#endif
        if (ZFS_XA_NS_PREFIX_FORBIDDEN(name))
                return (-EINVAL);
        if (!(ITOZSB(ip)->z_flags & ZSB_XATTR))
                return (-EOPNOTSUPP);

        /*
         * Try to look up the name with the namespace prefix first for
         * compatibility with xattrs from this platform.  If that fails,
         * try again without the namespace prefix for compatibility with
         * other platforms.
         */
        char *xattr_name = kmem_asprintf("%s%s", XATTR_USER_PREFIX, name);
        error = zpl_xattr_get(ip, xattr_name, value, size);
        kmem_strfree(xattr_name);
        if (error == -ENODATA)
                error = zpl_xattr_get(ip, name, value, size);

        return (error);
}
ZPL_XATTR_GET_WRAPPER(zpl_xattr_user_get);

static int
__zpl_xattr_user_set(struct inode *ip, const char *name,
    const void *value, size_t size, int flags)
{
        int error = 0;
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") == 0)
                return (-EINVAL);
#endif
        if (ZFS_XA_NS_PREFIX_FORBIDDEN(name))
                return (-EINVAL);
        if (!(ITOZSB(ip)->z_flags & ZSB_XATTR))
                return (-EOPNOTSUPP);

        /*
         * Remove alternate compat version of the xattr so we only set the
         * version specified by the zfs_xattr_compat tunable.
         *
         * The following flags must be handled correctly:
         *
         *   XATTR_CREATE: fail if xattr already exists
         *   XATTR_REPLACE: fail if xattr does not exist
         */
        char *prefixed_name = kmem_asprintf("%s%s", XATTR_USER_PREFIX, name);
        const char *clear_name, *set_name;
        if (zfs_xattr_compat) {
                clear_name = prefixed_name;
                set_name = name;
        } else {
                clear_name = name;
                set_name = prefixed_name;
        }
        /*
         * Clear the old value with the alternative name format, if it exists.
         */
        error = zpl_xattr_set(ip, clear_name, NULL, 0, flags);
        /*
         * XATTR_CREATE was specified and we failed to clear the xattr
         * because it already exists.  Stop here.
         */
        if (error == -EEXIST)
                goto out;
        /*
         * If XATTR_REPLACE was specified and we succeeded to clear
         * an xattr, we don't need to replace anything when setting
         * the new value.  If we failed with -ENODATA that's fine,
         * there was nothing to be cleared and we can ignore the error.
         */
        if (error == 0)
                flags &= ~XATTR_REPLACE;
        /*
         * Set the new value with the configured name format.
         */
        error = zpl_xattr_set(ip, set_name, value, size, flags);
out:
        kmem_strfree(prefixed_name);
        return (error);
}
ZPL_XATTR_SET_WRAPPER(zpl_xattr_user_set);

static xattr_handler_t zpl_xattr_user_handler =
{
        .prefix = XATTR_USER_PREFIX,
        .list   = zpl_xattr_user_list,
        .get    = zpl_xattr_user_get,
        .set    = zpl_xattr_user_set,
};

/*
 * Trusted extended attributes
 *
 * "Trusted extended attributes are visible and accessible only to
 * processes that have the CAP_SYS_ADMIN capability.  Attributes in this
 * class are used to implement mechanisms in user space (i.e., outside
 * the kernel) which keep information in extended attributes to which
 * ordinary processes should not have access." - xattr(7)
 */
static int
__zpl_xattr_trusted_list(struct inode *ip, char *list, size_t list_size,
    const char *name, size_t name_len)
{
        return (capable(CAP_SYS_ADMIN));
}
ZPL_XATTR_LIST_WRAPPER(zpl_xattr_trusted_list);

static int
__zpl_xattr_trusted_get(struct inode *ip, const char *name,
    void *value, size_t size)
{
        char *xattr_name;
        int error;

        if (!capable(CAP_SYS_ADMIN))
                return (-EACCES);
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") == 0)
                return (-EINVAL);
#endif
        xattr_name = kmem_asprintf("%s%s", XATTR_TRUSTED_PREFIX, name);
        error = zpl_xattr_get(ip, xattr_name, value, size);
        kmem_strfree(xattr_name);

        return (error);
}
ZPL_XATTR_GET_WRAPPER(zpl_xattr_trusted_get);

static int
__zpl_xattr_trusted_set(struct inode *ip, const char *name,
    const void *value, size_t size, int flags)
{
        char *xattr_name;
        int error;

        if (!capable(CAP_SYS_ADMIN))
                return (-EACCES);
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") == 0)
                return (-EINVAL);
#endif
        xattr_name = kmem_asprintf("%s%s", XATTR_TRUSTED_PREFIX, name);
        error = zpl_xattr_set(ip, xattr_name, value, size, flags);
        kmem_strfree(xattr_name);

        return (error);
}
ZPL_XATTR_SET_WRAPPER(zpl_xattr_trusted_set);

static xattr_handler_t zpl_xattr_trusted_handler = {
        .prefix = XATTR_TRUSTED_PREFIX,
        .list   = zpl_xattr_trusted_list,
        .get    = zpl_xattr_trusted_get,
        .set    = zpl_xattr_trusted_set,
};

/*
 * Extended security attributes
 *
 * "The security attribute namespace is used by kernel security modules,
 * such as Security Enhanced Linux, and also to implement file
 * capabilities (see capabilities(7)).  Read and write access
 * permissions to security attributes depend on the policy implemented
 * for each security attribute by the security module.  When no security
 * module is loaded, all processes have read access to extended security
 * attributes, and write access is limited to processes that have the
 * CAP_SYS_ADMIN capability." - xattr(7)
 */
static int
__zpl_xattr_security_list(struct inode *ip, char *list, size_t list_size,
    const char *name, size_t name_len)
{
        return (1);
}
ZPL_XATTR_LIST_WRAPPER(zpl_xattr_security_list);

static int
__zpl_xattr_security_get(struct inode *ip, const char *name,
    void *value, size_t size)
{
        char *xattr_name;
        int error;
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") == 0)
                return (-EINVAL);
#endif
        xattr_name = kmem_asprintf("%s%s", XATTR_SECURITY_PREFIX, name);
        error = zpl_xattr_get(ip, xattr_name, value, size);
        kmem_strfree(xattr_name);

        return (error);
}
ZPL_XATTR_GET_WRAPPER(zpl_xattr_security_get);

static int
__zpl_xattr_security_set(struct inode *ip, const char *name,
    const void *value, size_t size, int flags)
{
        char *xattr_name;
        int error;
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") == 0)
                return (-EINVAL);
#endif
        xattr_name = kmem_asprintf("%s%s", XATTR_SECURITY_PREFIX, name);
        error = zpl_xattr_set(ip, xattr_name, value, size, flags);
        kmem_strfree(xattr_name);

        return (error);
}
ZPL_XATTR_SET_WRAPPER(zpl_xattr_security_set);

static int
zpl_xattr_security_init_impl(struct inode *ip, const struct xattr *xattrs,
    void *fs_info)
{
        const struct xattr *xattr;
        int error = 0;

        for (xattr = xattrs; xattr->name != NULL; xattr++) {
                error = __zpl_xattr_security_set(ip,
                    xattr->name, xattr->value, xattr->value_len, 0);

                if (error < 0)
                        break;
        }

        return (error);
}

int
zpl_xattr_security_init(struct inode *ip, struct inode *dip,
    const struct qstr *qstr)
{
        return security_inode_init_security(ip, dip, qstr,
            &zpl_xattr_security_init_impl, NULL);
}

/*
 * Security xattr namespace handlers.
 */
static xattr_handler_t zpl_xattr_security_handler = {
        .prefix = XATTR_SECURITY_PREFIX,
        .list   = zpl_xattr_security_list,
        .get    = zpl_xattr_security_get,
        .set    = zpl_xattr_security_set,
};

/*
 * Extended system attributes
 *
 * "Extended system attributes are used by the kernel to store system
 * objects such as Access Control Lists.  Read and write access permissions
 * to system attributes depend on the policy implemented for each system
 * attribute implemented by filesystems in the kernel." - xattr(7)
 */
#ifdef CONFIG_FS_POSIX_ACL
static int
zpl_set_acl_impl(struct inode *ip, struct posix_acl *acl, int type)
{
        char *name, *value = NULL;
        int error = 0;
        size_t size = 0;

        if (S_ISLNK(ip->i_mode))
                return (-EOPNOTSUPP);

        switch (type) {
        case ACL_TYPE_ACCESS:
                name = XATTR_NAME_POSIX_ACL_ACCESS;
                if (acl) {
                        umode_t mode = ip->i_mode;
                        error = posix_acl_equiv_mode(acl, &mode);
                        if (error < 0) {
                                return (error);
                        } else {
                                /*
                                 * The mode bits will have been set by
                                 * ->zfs_setattr()->zfs_acl_chmod_setattr()
                                 * using the ZFS ACL conversion.  If they
                                 * differ from the Posix ACL conversion dirty
                                 * the inode to write the Posix mode bits.
                                 */
                                if (ip->i_mode != mode) {
                                        ip->i_mode = mode;
                                        ip->i_ctime = current_time(ip);
                                        zfs_mark_inode_dirty(ip);
                                }

                                if (error == 0)
                                        acl = NULL;
                        }
                }
                break;

        case ACL_TYPE_DEFAULT:
                name = XATTR_NAME_POSIX_ACL_DEFAULT;
                if (!S_ISDIR(ip->i_mode))
                        return (acl ? -EACCES : 0);
                break;

        default:
                return (-EINVAL);
        }

        if (acl) {
                size = posix_acl_xattr_size(acl->a_count);
                value = kmem_alloc(size, KM_SLEEP);

                error = zpl_acl_to_xattr(acl, value, size);
                if (error < 0) {
                        kmem_free(value, size);
                        return (error);
                }
        }

        error = zpl_xattr_set(ip, name, value, size, 0);
        if (value)
                kmem_free(value, size);

        if (!error) {
                if (acl)
                        zpl_set_cached_acl(ip, type, acl);
                else
                        zpl_forget_cached_acl(ip, type);
        }

        return (error);
}

#ifdef HAVE_SET_ACL
int
#ifdef HAVE_SET_ACL_USERNS
zpl_set_acl(struct user_namespace *userns, struct inode *ip,
    struct posix_acl *acl, int type)
#else
zpl_set_acl(struct inode *ip, struct posix_acl *acl, int type)
#endif /* HAVE_SET_ACL_USERNS */
{
        return (zpl_set_acl_impl(ip, acl, type));
}
#endif /* HAVE_SET_ACL */

static struct posix_acl *
zpl_get_acl_impl(struct inode *ip, int type)
{
        struct posix_acl *acl;
        void *value = NULL;
        char *name;

        /*
         * As of Linux 3.14, the kernel get_acl will check this for us.
         * Also as of Linux 4.7, comparing against ACL_NOT_CACHED is wrong
         * as the kernel get_acl will set it to temporary sentinel value.
         */
#ifndef HAVE_KERNEL_GET_ACL_HANDLE_CACHE
        acl = get_cached_acl(ip, type);
        if (acl != ACL_NOT_CACHED)
                return (acl);
#endif

        switch (type) {
        case ACL_TYPE_ACCESS:
                name = XATTR_NAME_POSIX_ACL_ACCESS;
                break;
        case ACL_TYPE_DEFAULT:
                name = XATTR_NAME_POSIX_ACL_DEFAULT;
                break;
        default:
                return (ERR_PTR(-EINVAL));
        }

        int size = zpl_xattr_get(ip, name, NULL, 0);
        if (size > 0) {
                value = kmem_alloc(size, KM_SLEEP);
                size = zpl_xattr_get(ip, name, value, size);
        }

        if (size > 0) {
                acl = zpl_acl_from_xattr(value, size);
        } else if (size == -ENODATA || size == -ENOSYS) {
                acl = NULL;
        } else {
                acl = ERR_PTR(-EIO);
        }

        if (size > 0)
                kmem_free(value, size);

        /* As of Linux 4.7, the kernel get_acl will set this for us */
#ifndef HAVE_KERNEL_GET_ACL_HANDLE_CACHE
        if (!IS_ERR(acl))
                zpl_set_cached_acl(ip, type, acl);
#endif

        return (acl);
}

#if defined(HAVE_GET_ACL_RCU)
struct posix_acl *
zpl_get_acl(struct inode *ip, int type, bool rcu)
{
        if (rcu)
                return (ERR_PTR(-ECHILD));

        return (zpl_get_acl_impl(ip, type));
}
#elif defined(HAVE_GET_ACL)
struct posix_acl *
zpl_get_acl(struct inode *ip, int type)
{
        return (zpl_get_acl_impl(ip, type));
}
#else
#error "Unsupported iops->get_acl() implementation"
#endif /* HAVE_GET_ACL_RCU */

int
zpl_init_acl(struct inode *ip, struct inode *dir)
{
        struct posix_acl *acl = NULL;
        int error = 0;

        if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_POSIX)
                return (0);

        if (!S_ISLNK(ip->i_mode)) {
                acl = zpl_get_acl_impl(dir, ACL_TYPE_DEFAULT);
                if (IS_ERR(acl))
                        return (PTR_ERR(acl));
                if (!acl) {
                        ip->i_mode &= ~current_umask();
                        ip->i_ctime = current_time(ip);
                        zfs_mark_inode_dirty(ip);
                        return (0);
                }
        }

        if (acl) {
                umode_t mode;

                if (S_ISDIR(ip->i_mode)) {
                        error = zpl_set_acl_impl(ip, acl, ACL_TYPE_DEFAULT);
                        if (error)
                                goto out;
                }

                mode = ip->i_mode;
                error = __posix_acl_create(&acl, GFP_KERNEL, &mode);
                if (error >= 0) {
                        ip->i_mode = mode;
                        zfs_mark_inode_dirty(ip);
                        if (error > 0) {
                                error = zpl_set_acl_impl(ip, acl,
                                    ACL_TYPE_ACCESS);
                        }
                }
        }
out:
        zpl_posix_acl_release(acl);

        return (error);
}

int
zpl_chmod_acl(struct inode *ip)
{
        struct posix_acl *acl;
        int error;

        if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_POSIX)
                return (0);

        if (S_ISLNK(ip->i_mode))
                return (-EOPNOTSUPP);

        acl = zpl_get_acl_impl(ip, ACL_TYPE_ACCESS);
        if (IS_ERR(acl) || !acl)
                return (PTR_ERR(acl));

        error = __posix_acl_chmod(&acl, GFP_KERNEL, ip->i_mode);
        if (!error)
                error = zpl_set_acl_impl(ip, acl, ACL_TYPE_ACCESS);

        zpl_posix_acl_release(acl);

        return (error);
}

static int
__zpl_xattr_acl_list_access(struct inode *ip, char *list, size_t list_size,
    const char *name, size_t name_len)
{
        char *xattr_name = XATTR_NAME_POSIX_ACL_ACCESS;
        size_t xattr_size = sizeof (XATTR_NAME_POSIX_ACL_ACCESS);

        if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_POSIX)
                return (0);

        if (list && xattr_size <= list_size)
                memcpy(list, xattr_name, xattr_size);

        return (xattr_size);
}
ZPL_XATTR_LIST_WRAPPER(zpl_xattr_acl_list_access);

static int
__zpl_xattr_acl_list_default(struct inode *ip, char *list, size_t list_size,
    const char *name, size_t name_len)
{
        char *xattr_name = XATTR_NAME_POSIX_ACL_DEFAULT;
        size_t xattr_size = sizeof (XATTR_NAME_POSIX_ACL_DEFAULT);

        if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_POSIX)
                return (0);

        if (list && xattr_size <= list_size)
                memcpy(list, xattr_name, xattr_size);

        return (xattr_size);
}
ZPL_XATTR_LIST_WRAPPER(zpl_xattr_acl_list_default);

static int
__zpl_xattr_acl_get_access(struct inode *ip, const char *name,
    void *buffer, size_t size)
{
        struct posix_acl *acl;
        int type = ACL_TYPE_ACCESS;
        int error;
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") != 0)
                return (-EINVAL);
#endif
        if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_POSIX)
                return (-EOPNOTSUPP);

        acl = zpl_get_acl_impl(ip, type);
        if (IS_ERR(acl))
                return (PTR_ERR(acl));
        if (acl == NULL)
                return (-ENODATA);

        error = zpl_acl_to_xattr(acl, buffer, size);
        zpl_posix_acl_release(acl);

        return (error);
}
ZPL_XATTR_GET_WRAPPER(zpl_xattr_acl_get_access);

static int
__zpl_xattr_acl_get_default(struct inode *ip, const char *name,
    void *buffer, size_t size)
{
        struct posix_acl *acl;
        int type = ACL_TYPE_DEFAULT;
        int error;
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") != 0)
                return (-EINVAL);
#endif
        if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_POSIX)
                return (-EOPNOTSUPP);

        acl = zpl_get_acl_impl(ip, type);
        if (IS_ERR(acl))
                return (PTR_ERR(acl));
        if (acl == NULL)
                return (-ENODATA);

        error = zpl_acl_to_xattr(acl, buffer, size);
        zpl_posix_acl_release(acl);

        return (error);
}
ZPL_XATTR_GET_WRAPPER(zpl_xattr_acl_get_default);

static int
__zpl_xattr_acl_set_access(struct inode *ip, const char *name,
    const void *value, size_t size, int flags)
{
        struct posix_acl *acl;
        int type = ACL_TYPE_ACCESS;
        int error = 0;
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") != 0)
                return (-EINVAL);
#endif
        if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_POSIX)
                return (-EOPNOTSUPP);

        if (!zpl_inode_owner_or_capable(kcred->user_ns, ip))
                return (-EPERM);

        if (value) {
                acl = zpl_acl_from_xattr(value, size);
                if (IS_ERR(acl))
                        return (PTR_ERR(acl));
                else if (acl) {
                        error = zpl_posix_acl_valid(ip, acl);
                        if (error) {
                                zpl_posix_acl_release(acl);
                                return (error);
                        }
                }
        } else {
                acl = NULL;
        }
        error = zpl_set_acl_impl(ip, acl, type);
        zpl_posix_acl_release(acl);

        return (error);
}
ZPL_XATTR_SET_WRAPPER(zpl_xattr_acl_set_access);

static int
__zpl_xattr_acl_set_default(struct inode *ip, const char *name,
    const void *value, size_t size, int flags)
{
        struct posix_acl *acl;
        int type = ACL_TYPE_DEFAULT;
        int error = 0;
        /* xattr_resolve_name will do this for us if this is defined */
#ifndef HAVE_XATTR_HANDLER_NAME
        if (strcmp(name, "") != 0)
                return (-EINVAL);
#endif
        if (ITOZSB(ip)->z_acl_type != ZFS_ACLTYPE_POSIX)
                return (-EOPNOTSUPP);

        if (!zpl_inode_owner_or_capable(kcred->user_ns, ip))
                return (-EPERM);

        if (value) {
                acl = zpl_acl_from_xattr(value, size);
                if (IS_ERR(acl))
                        return (PTR_ERR(acl));
                else if (acl) {
                        error = zpl_posix_acl_valid(ip, acl);
                        if (error) {
                                zpl_posix_acl_release(acl);
                                return (error);
                        }
                }
        } else {
                acl = NULL;
        }

        error = zpl_set_acl_impl(ip, acl, type);
        zpl_posix_acl_release(acl);

        return (error);
}
ZPL_XATTR_SET_WRAPPER(zpl_xattr_acl_set_default);

/*
 * ACL access xattr namespace handlers.
 *
 * Use .name instead of .prefix when available. xattr_resolve_name will match
 * whole name and reject anything that has .name only as prefix.
 */
static xattr_handler_t zpl_xattr_acl_access_handler = {
#ifdef HAVE_XATTR_HANDLER_NAME
        .name   = XATTR_NAME_POSIX_ACL_ACCESS,
#else
        .prefix = XATTR_NAME_POSIX_ACL_ACCESS,
#endif
        .list   = zpl_xattr_acl_list_access,
        .get    = zpl_xattr_acl_get_access,
        .set    = zpl_xattr_acl_set_access,
#if defined(HAVE_XATTR_LIST_SIMPLE) || \
    defined(HAVE_XATTR_LIST_DENTRY) || \
    defined(HAVE_XATTR_LIST_HANDLER)
        .flags  = ACL_TYPE_ACCESS,
#endif
};

/*
 * ACL default xattr namespace handlers.
 *
 * Use .name instead of .prefix when available. xattr_resolve_name will match
 * whole name and reject anything that has .name only as prefix.
 */
static xattr_handler_t zpl_xattr_acl_default_handler = {
#ifdef HAVE_XATTR_HANDLER_NAME
        .name   = XATTR_NAME_POSIX_ACL_DEFAULT,
#else
        .prefix = XATTR_NAME_POSIX_ACL_DEFAULT,
#endif
        .list   = zpl_xattr_acl_list_default,
        .get    = zpl_xattr_acl_get_default,
        .set    = zpl_xattr_acl_set_default,
#if defined(HAVE_XATTR_LIST_SIMPLE) || \
    defined(HAVE_XATTR_LIST_DENTRY) || \
    defined(HAVE_XATTR_LIST_HANDLER)
        .flags  = ACL_TYPE_DEFAULT,
#endif
};

#endif /* CONFIG_FS_POSIX_ACL */

xattr_handler_t *zpl_xattr_handlers[] = {
        &zpl_xattr_security_handler,
        &zpl_xattr_trusted_handler,
        &zpl_xattr_user_handler,
#ifdef CONFIG_FS_POSIX_ACL
        &zpl_xattr_acl_access_handler,
        &zpl_xattr_acl_default_handler,
#endif /* CONFIG_FS_POSIX_ACL */
        NULL
};

static const struct xattr_handler *
zpl_xattr_handler(const char *name)
{
        if (strncmp(name, XATTR_USER_PREFIX,
            XATTR_USER_PREFIX_LEN) == 0)
                return (&zpl_xattr_user_handler);

        if (strncmp(name, XATTR_TRUSTED_PREFIX,
            XATTR_TRUSTED_PREFIX_LEN) == 0)
                return (&zpl_xattr_trusted_handler);

        if (strncmp(name, XATTR_SECURITY_PREFIX,
            XATTR_SECURITY_PREFIX_LEN) == 0)
                return (&zpl_xattr_security_handler);

#ifdef CONFIG_FS_POSIX_ACL
        if (strncmp(name, XATTR_NAME_POSIX_ACL_ACCESS,
            sizeof (XATTR_NAME_POSIX_ACL_ACCESS)) == 0)
                return (&zpl_xattr_acl_access_handler);

        if (strncmp(name, XATTR_NAME_POSIX_ACL_DEFAULT,
            sizeof (XATTR_NAME_POSIX_ACL_DEFAULT)) == 0)
                return (&zpl_xattr_acl_default_handler);
#endif /* CONFIG_FS_POSIX_ACL */

        return (NULL);
}

static enum xattr_permission
zpl_xattr_permission(xattr_filldir_t *xf, const char *name, int name_len)
{
        const struct xattr_handler *handler;
        struct dentry *d __maybe_unused = xf->dentry;
        enum xattr_permission perm = XAPERM_ALLOW;

        handler = zpl_xattr_handler(name);
        if (handler == NULL) {
                /* Do not expose FreeBSD system namespace xattrs. */
                if (ZFS_XA_NS_PREFIX_MATCH(FREEBSD, name))
                        return (XAPERM_DENY);
                /*
                 * Anything that doesn't match a known namespace gets put in the
                 * user namespace for compatibility with other platforms.
                 */
                perm = XAPERM_COMPAT;
                handler = &zpl_xattr_user_handler;
        }

        if (handler->list) {
#if defined(HAVE_XATTR_LIST_SIMPLE)
                if (!handler->list(d))
                        return (XAPERM_DENY);
#elif defined(HAVE_XATTR_LIST_DENTRY)
                if (!handler->list(d, NULL, 0, name, name_len, 0))
                        return (XAPERM_DENY);
#elif defined(HAVE_XATTR_LIST_HANDLER)
                if (!handler->list(handler, d, NULL, 0, name, name_len))
                        return (XAPERM_DENY);
#endif
        }

        return (perm);
}

#if !defined(HAVE_POSIX_ACL_RELEASE) || defined(HAVE_POSIX_ACL_RELEASE_GPL_ONLY)
struct acl_rel_struct {
        struct acl_rel_struct *next;
        struct posix_acl *acl;
        clock_t time;
};

#define ACL_REL_GRACE   (60*HZ)
#define ACL_REL_WINDOW  (1*HZ)
#define ACL_REL_SCHED   (ACL_REL_GRACE+ACL_REL_WINDOW)

/*
 * Lockless multi-producer single-consumer fifo list.
 * Nodes are added to tail and removed from head. Tail pointer is our
 * synchronization point. It always points to the next pointer of the last
 * node, or head if list is empty.
 */
static struct acl_rel_struct *acl_rel_head = NULL;
static struct acl_rel_struct **acl_rel_tail = &acl_rel_head;

static void
zpl_posix_acl_free(void *arg)
{
        struct acl_rel_struct *freelist = NULL;
        struct acl_rel_struct *a;
        clock_t new_time;
        boolean_t refire = B_FALSE;

        ASSERT3P(acl_rel_head, !=, NULL);
        while (acl_rel_head) {
                a = acl_rel_head;
                if (ddi_get_lbolt() - a->time >= ACL_REL_GRACE) {
                        /*
                         * If a is the last node we need to reset tail, but we
                         * need to use cmpxchg to make sure it is still the
                         * last node.
                         */
                        if (acl_rel_tail == &a->next) {
                                acl_rel_head = NULL;
                                if (cmpxchg(&acl_rel_tail, &a->next,
                                    &acl_rel_head) == &a->next) {
                                        ASSERT3P(a->next, ==, NULL);
                                        a->next = freelist;
                                        freelist = a;
                                        break;
                                }
                        }
                        /*
                         * a is not last node, make sure next pointer is set
                         * by the adder and advance the head.
                         */
                        while (READ_ONCE(a->next) == NULL)
                                cpu_relax();
                        acl_rel_head = a->next;
                        a->next = freelist;
                        freelist = a;
                } else {
                        /*
                         * a is still in grace period. We are responsible to
                         * reschedule the free task, since adder will only do
                         * so if list is empty.
                         */
                        new_time = a->time + ACL_REL_SCHED;
                        refire = B_TRUE;
                        break;
                }
        }

        if (refire)
                taskq_dispatch_delay(system_delay_taskq, zpl_posix_acl_free,
                    NULL, TQ_SLEEP, new_time);

        while (freelist) {
                a = freelist;
                freelist = a->next;
                kfree(a->acl);
                kmem_free(a, sizeof (struct acl_rel_struct));
        }
}

void
zpl_posix_acl_release_impl(struct posix_acl *acl)
{
        struct acl_rel_struct *a, **prev;

        a = kmem_alloc(sizeof (struct acl_rel_struct), KM_SLEEP);
        a->next = NULL;
        a->acl = acl;
        a->time = ddi_get_lbolt();
        /* atomically points tail to us and get the previous tail */
        prev = xchg(&acl_rel_tail, &a->next);
        ASSERT3P(*prev, ==, NULL);
        *prev = a;
        /* if it was empty before, schedule the free task */
        if (prev == &acl_rel_head)
                taskq_dispatch_delay(system_delay_taskq, zpl_posix_acl_free,
                    NULL, TQ_SLEEP, ddi_get_lbolt() + ACL_REL_SCHED);
}
#endif

ZFS_MODULE_PARAM(zfs, zfs_, xattr_compat, INT, ZMOD_RW,
        "Use legacy ZFS xattr naming for writing new user namespace xattrs");