mm: fix exec activate_mm vs TLB shootdown and lazy tlb switching race

[linux/fpc-iii.git] / fs / reiserfs / xattr.c

// SPDX-License-Identifier: GPL-2.0
/*
 * linux/fs/reiserfs/xattr.c
 *
 * Copyright (c) 2002 by Jeff Mahoney, <jeffm@suse.com>
 *
 */

/*
 * In order to implement EA/ACLs in a clean, backwards compatible manner,
 * they are implemented as files in a "private" directory.
 * Each EA is in it's own file, with the directory layout like so (/ is assumed
 * to be relative to fs root). Inside the /.reiserfs_priv/xattrs directory,
 * directories named using the capital-hex form of the objectid and
 * generation number are used. Inside each directory are individual files
 * named with the name of the extended attribute.
 *
 * So, for objectid 12648430, we could have:
 * /.reiserfs_priv/xattrs/C0FFEE.0/system.posix_acl_access
 * /.reiserfs_priv/xattrs/C0FFEE.0/system.posix_acl_default
 * /.reiserfs_priv/xattrs/C0FFEE.0/user.Content-Type
 * .. or similar.
 *
 * The file contents are the text of the EA. The size is known based on the
 * stat data describing the file.
 *
 * In the case of system.posix_acl_access and system.posix_acl_default, since
 * these are special cases for filesystem ACLs, they are interpreted by the
 * kernel, in addition, they are negatively and positively cached and attached
 * to the inode so that unnecessary lookups are avoided.
 *
 * Locking works like so:
 * Directory components (xattr root, xattr dir) are protectd by their i_mutex.
 * The xattrs themselves are protected by the xattr_sem.
 */

#include "reiserfs.h"
#include <linux/capability.h>
#include <linux/dcache.h>
#include <linux/namei.h>
#include <linux/errno.h>
#include <linux/gfp.h>
#include <linux/fs.h>
#include <linux/file.h>
#include <linux/pagemap.h>
#include <linux/xattr.h>
#include "xattr.h"
#include "acl.h"
#include <linux/uaccess.h>
#include <net/checksum.h>
#include <linux/stat.h>
#include <linux/quotaops.h>
#include <linux/security.h>
#include <linux/posix_acl_xattr.h>

#define PRIVROOT_NAME ".reiserfs_priv"
#define XAROOT_NAME   "xattrs"


/*
 * Helpers for inode ops. We do this so that we don't have all the VFS
 * overhead and also for proper i_mutex annotation.
 * dir->i_mutex must be held for all of them.
 */
#ifdef CONFIG_REISERFS_FS_XATTR
static int xattr_create(struct inode *dir, struct dentry *dentry, int mode)
{
        BUG_ON(!inode_is_locked(dir));
        return dir->i_op->create(dir, dentry, mode, true);
}
#endif

static int xattr_mkdir(struct inode *dir, struct dentry *dentry, umode_t mode)
{
        BUG_ON(!inode_is_locked(dir));
        return dir->i_op->mkdir(dir, dentry, mode);
}

/*
 * We use I_MUTEX_CHILD here to silence lockdep. It's safe because xattr
 * mutation ops aren't called during rename or splace, which are the
 * only other users of I_MUTEX_CHILD. It violates the ordering, but that's
 * better than allocating another subclass just for this code.
 */
static int xattr_unlink(struct inode *dir, struct dentry *dentry)
{
        int error;

        BUG_ON(!inode_is_locked(dir));

        inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);
        error = dir->i_op->unlink(dir, dentry);
        inode_unlock(d_inode(dentry));

        if (!error)
                d_delete(dentry);
        return error;
}

static int xattr_rmdir(struct inode *dir, struct dentry *dentry)
{
        int error;

        BUG_ON(!inode_is_locked(dir));

        inode_lock_nested(d_inode(dentry), I_MUTEX_CHILD);
        error = dir->i_op->rmdir(dir, dentry);
        if (!error)
                d_inode(dentry)->i_flags |= S_DEAD;
        inode_unlock(d_inode(dentry));
        if (!error)
                d_delete(dentry);

        return error;
}

#define xattr_may_create(flags) (!flags || flags & XATTR_CREATE)

static struct dentry *open_xa_root(struct super_block *sb, int flags)
{
        struct dentry *privroot = REISERFS_SB(sb)->priv_root;
        struct dentry *xaroot;

        if (d_really_is_negative(privroot))
                return ERR_PTR(-EOPNOTSUPP);

        inode_lock_nested(d_inode(privroot), I_MUTEX_XATTR);

        xaroot = dget(REISERFS_SB(sb)->xattr_root);
        if (!xaroot)
                xaroot = ERR_PTR(-EOPNOTSUPP);
        else if (d_really_is_negative(xaroot)) {
                int err = -ENODATA;

                if (xattr_may_create(flags))
                        err = xattr_mkdir(d_inode(privroot), xaroot, 0700);
                if (err) {
                        dput(xaroot);
                        xaroot = ERR_PTR(err);
                }
        }

        inode_unlock(d_inode(privroot));
        return xaroot;
}

static struct dentry *open_xa_dir(const struct inode *inode, int flags)
{
        struct dentry *xaroot, *xadir;
        char namebuf[17];

        xaroot = open_xa_root(inode->i_sb, flags);
        if (IS_ERR(xaroot))
                return xaroot;

        snprintf(namebuf, sizeof(namebuf), "%X.%X",
                 le32_to_cpu(INODE_PKEY(inode)->k_objectid),
                 inode->i_generation);

        inode_lock_nested(d_inode(xaroot), I_MUTEX_XATTR);

        xadir = lookup_one_len(namebuf, xaroot, strlen(namebuf));
        if (!IS_ERR(xadir) && d_really_is_negative(xadir)) {
                int err = -ENODATA;

                if (xattr_may_create(flags))
                        err = xattr_mkdir(d_inode(xaroot), xadir, 0700);
                if (err) {
                        dput(xadir);
                        xadir = ERR_PTR(err);
                }
        }

        inode_unlock(d_inode(xaroot));
        dput(xaroot);
        return xadir;
}

/*
 * The following are side effects of other operations that aren't explicitly
 * modifying extended attributes. This includes operations such as permissions
 * or ownership changes, object deletions, etc.
 */
struct reiserfs_dentry_buf {
        struct dir_context ctx;
        struct dentry *xadir;
        int count;
        int err;
        struct dentry *dentries[8];
};

static int
fill_with_dentries(struct dir_context *ctx, const char *name, int namelen,
                   loff_t offset, u64 ino, unsigned int d_type)
{
        struct reiserfs_dentry_buf *dbuf =
                container_of(ctx, struct reiserfs_dentry_buf, ctx);
        struct dentry *dentry;

        WARN_ON_ONCE(!inode_is_locked(d_inode(dbuf->xadir)));

        if (dbuf->count == ARRAY_SIZE(dbuf->dentries))
                return -ENOSPC;

        if (name[0] == '.' && (namelen < 2 ||
                               (namelen == 2 && name[1] == '.')))
                return 0;

        dentry = lookup_one_len(name, dbuf->xadir, namelen);
        if (IS_ERR(dentry)) {
                dbuf->err = PTR_ERR(dentry);
                return PTR_ERR(dentry);
        } else if (d_really_is_negative(dentry)) {
                /* A directory entry exists, but no file? */
                reiserfs_error(dentry->d_sb, "xattr-20003",
                               "Corrupted directory: xattr %pd listed but "
                               "not found for file %pd.\n",
                               dentry, dbuf->xadir);
                dput(dentry);
                dbuf->err = -EIO;
                return -EIO;
        }

        dbuf->dentries[dbuf->count++] = dentry;
        return 0;
}

static void
cleanup_dentry_buf(struct reiserfs_dentry_buf *buf)
{
        int i;

        for (i = 0; i < buf->count; i++)
                if (buf->dentries[i])
                        dput(buf->dentries[i]);
}

static int reiserfs_for_each_xattr(struct inode *inode,
                                   int (*action)(struct dentry *, void *),
                                   void *data)
{
        struct dentry *dir;
        int i, err = 0;
        struct reiserfs_dentry_buf buf = {
                .ctx.actor = fill_with_dentries,
        };

        /* Skip out, an xattr has no xattrs associated with it */
        if (IS_PRIVATE(inode) || get_inode_sd_version(inode) == STAT_DATA_V1)
                return 0;

        dir = open_xa_dir(inode, XATTR_REPLACE);
        if (IS_ERR(dir)) {
                err = PTR_ERR(dir);
                goto out;
        } else if (d_really_is_negative(dir)) {
                err = 0;
                goto out_dir;
        }

        inode_lock_nested(d_inode(dir), I_MUTEX_XATTR);

        buf.xadir = dir;
        while (1) {
                err = reiserfs_readdir_inode(d_inode(dir), &buf.ctx);
                if (err)
                        break;
                if (buf.err) {
                        err = buf.err;
                        break;
                }
                if (!buf.count)
                        break;
                for (i = 0; !err && i < buf.count && buf.dentries[i]; i++) {
                        struct dentry *dentry = buf.dentries[i];

                        if (!d_is_dir(dentry))
                                err = action(dentry, data);

                        dput(dentry);
                        buf.dentries[i] = NULL;
                }
                if (err)
                        break;
                buf.count = 0;
        }
        inode_unlock(d_inode(dir));

        cleanup_dentry_buf(&buf);

        if (!err) {
                /*
                 * We start a transaction here to avoid a ABBA situation
                 * between the xattr root's i_mutex and the journal lock.
                 * This doesn't incur much additional overhead since the
                 * new transaction will just nest inside the
                 * outer transaction.
                 */
                int blocks = JOURNAL_PER_BALANCE_CNT * 2 + 2 +
                             4 * REISERFS_QUOTA_TRANS_BLOCKS(inode->i_sb);
                struct reiserfs_transaction_handle th;

                reiserfs_write_lock(inode->i_sb);
                err = journal_begin(&th, inode->i_sb, blocks);
                reiserfs_write_unlock(inode->i_sb);
                if (!err) {
                        int jerror;

                        inode_lock_nested(d_inode(dir->d_parent),
                                          I_MUTEX_XATTR);
                        err = action(dir, data);
                        reiserfs_write_lock(inode->i_sb);
                        jerror = journal_end(&th);
                        reiserfs_write_unlock(inode->i_sb);
                        inode_unlock(d_inode(dir->d_parent));
                        err = jerror ?: err;
                }
        }
out_dir:
        dput(dir);
out:
        /*
         * -ENODATA: this object doesn't have any xattrs
         * -EOPNOTSUPP: this file system doesn't have xattrs enabled on disk.
         * Neither are errors
         */
        if (err == -ENODATA || err == -EOPNOTSUPP)
                err = 0;
        return err;
}

static int delete_one_xattr(struct dentry *dentry, void *data)
{
        struct inode *dir = d_inode(dentry->d_parent);

        /* This is the xattr dir, handle specially. */
        if (d_is_dir(dentry))
                return xattr_rmdir(dir, dentry);

        return xattr_unlink(dir, dentry);
}

static int chown_one_xattr(struct dentry *dentry, void *data)
{
        struct iattr *attrs = data;
        int ia_valid = attrs->ia_valid;
        int err;

        /*
         * We only want the ownership bits. Otherwise, we'll do
         * things like change a directory to a regular file if
         * ATTR_MODE is set.
         */
        attrs->ia_valid &= (ATTR_UID|ATTR_GID);
        err = reiserfs_setattr(dentry, attrs);
        attrs->ia_valid = ia_valid;

        return err;
}

/* No i_mutex, but the inode is unconnected. */
int reiserfs_delete_xattrs(struct inode *inode)
{
        int err = reiserfs_for_each_xattr(inode, delete_one_xattr, NULL);

        if (err)
                reiserfs_warning(inode->i_sb, "jdm-20004",
                                 "Couldn't delete all xattrs (%d)\n", err);
        return err;
}

/* inode->i_mutex: down */
int reiserfs_chown_xattrs(struct inode *inode, struct iattr *attrs)
{
        int err = reiserfs_for_each_xattr(inode, chown_one_xattr, attrs);

        if (err)
                reiserfs_warning(inode->i_sb, "jdm-20007",
                                 "Couldn't chown all xattrs (%d)\n", err);
        return err;
}

#ifdef CONFIG_REISERFS_FS_XATTR
/*
 * Returns a dentry corresponding to a specific extended attribute file
 * for the inode. If flags allow, the file is created. Otherwise, a
 * valid or negative dentry, or an error is returned.
 */
static struct dentry *xattr_lookup(struct inode *inode, const char *name,
                                    int flags)
{
        struct dentry *xadir, *xafile;
        int err = 0;

        xadir = open_xa_dir(inode, flags);
        if (IS_ERR(xadir))
                return ERR_CAST(xadir);

        inode_lock_nested(d_inode(xadir), I_MUTEX_XATTR);
        xafile = lookup_one_len(name, xadir, strlen(name));
        if (IS_ERR(xafile)) {
                err = PTR_ERR(xafile);
                goto out;
        }

        if (d_really_is_positive(xafile) && (flags & XATTR_CREATE))
                err = -EEXIST;

        if (d_really_is_negative(xafile)) {
                err = -ENODATA;
                if (xattr_may_create(flags))
                        err = xattr_create(d_inode(xadir), xafile,
                                              0700|S_IFREG);
        }

        if (err)
                dput(xafile);
out:
        inode_unlock(d_inode(xadir));
        dput(xadir);
        if (err)
                return ERR_PTR(err);
        return xafile;
}

/* Internal operations on file data */
static inline void reiserfs_put_page(struct page *page)
{
        kunmap(page);
        put_page(page);
}

static struct page *reiserfs_get_page(struct inode *dir, size_t n)
{
        struct address_space *mapping = dir->i_mapping;
        struct page *page;
        /*
         * We can deadlock if we try to free dentries,
         * and an unlink/rmdir has just occurred - GFP_NOFS avoids this
         */
        mapping_set_gfp_mask(mapping, GFP_NOFS);
        page = read_mapping_page(mapping, n >> PAGE_SHIFT, NULL);
        if (!IS_ERR(page)) {
                kmap(page);
                if (PageError(page))
                        goto fail;
        }
        return page;

fail:
        reiserfs_put_page(page);
        return ERR_PTR(-EIO);
}

static inline __u32 xattr_hash(const char *msg, int len)
{
        return csum_partial(msg, len, 0);
}

int reiserfs_commit_write(struct file *f, struct page *page,
                          unsigned from, unsigned to);

static void update_ctime(struct inode *inode)
{
        struct timespec now = current_time(inode);

        if (inode_unhashed(inode) || !inode->i_nlink ||
            timespec_equal(&inode->i_ctime, &now))
                return;

        inode->i_ctime = current_time(inode);
        mark_inode_dirty(inode);
}

static int lookup_and_delete_xattr(struct inode *inode, const char *name)
{
        int err = 0;
        struct dentry *dentry, *xadir;

        xadir = open_xa_dir(inode, XATTR_REPLACE);
        if (IS_ERR(xadir))
                return PTR_ERR(xadir);

        inode_lock_nested(d_inode(xadir), I_MUTEX_XATTR);
        dentry = lookup_one_len(name, xadir, strlen(name));
        if (IS_ERR(dentry)) {
                err = PTR_ERR(dentry);
                goto out_dput;
        }

        if (d_really_is_positive(dentry)) {
                err = xattr_unlink(d_inode(xadir), dentry);
                update_ctime(inode);
        }

        dput(dentry);
out_dput:
        inode_unlock(d_inode(xadir));
        dput(xadir);
        return err;
}


/* Generic extended attribute operations that can be used by xa plugins */

/*
 * inode->i_mutex: down
 */
int
reiserfs_xattr_set_handle(struct reiserfs_transaction_handle *th,
                          struct inode *inode, const char *name,
                          const void *buffer, size_t buffer_size, int flags)
{
        int err = 0;
        struct dentry *dentry;
        struct page *page;
        char *data;
        size_t file_pos = 0;
        size_t buffer_pos = 0;
        size_t new_size;
        __u32 xahash = 0;

        if (get_inode_sd_version(inode) == STAT_DATA_V1)
                return -EOPNOTSUPP;

        if (!buffer) {
                err = lookup_and_delete_xattr(inode, name);
                return err;
        }

        dentry = xattr_lookup(inode, name, flags);
        if (IS_ERR(dentry))
                return PTR_ERR(dentry);

        down_write(&REISERFS_I(inode)->i_xattr_sem);

        xahash = xattr_hash(buffer, buffer_size);
        while (buffer_pos < buffer_size || buffer_pos == 0) {
                size_t chunk;
                size_t skip = 0;
                size_t page_offset = (file_pos & (PAGE_SIZE - 1));

                if (buffer_size - buffer_pos > PAGE_SIZE)
                        chunk = PAGE_SIZE;
                else
                        chunk = buffer_size - buffer_pos;

                page = reiserfs_get_page(d_inode(dentry), file_pos);
                if (IS_ERR(page)) {
                        err = PTR_ERR(page);
                        goto out_unlock;
                }

                lock_page(page);
                data = page_address(page);

                if (file_pos == 0) {
                        struct reiserfs_xattr_header *rxh;

                        skip = file_pos = sizeof(struct reiserfs_xattr_header);
                        if (chunk + skip > PAGE_SIZE)
                                chunk = PAGE_SIZE - skip;
                        rxh = (struct reiserfs_xattr_header *)data;
                        rxh->h_magic = cpu_to_le32(REISERFS_XATTR_MAGIC);
                        rxh->h_hash = cpu_to_le32(xahash);
                }

                reiserfs_write_lock(inode->i_sb);
                err = __reiserfs_write_begin(page, page_offset, chunk + skip);
                if (!err) {
                        if (buffer)
                                memcpy(data + skip, buffer + buffer_pos, chunk);
                        err = reiserfs_commit_write(NULL, page, page_offset,
                                                    page_offset + chunk +
                                                    skip);
                }
                reiserfs_write_unlock(inode->i_sb);
                unlock_page(page);
                reiserfs_put_page(page);
                buffer_pos += chunk;
                file_pos += chunk;
                skip = 0;
                if (err || buffer_size == 0 || !buffer)
                        break;
        }

        new_size = buffer_size + sizeof(struct reiserfs_xattr_header);
        if (!err && new_size < i_size_read(d_inode(dentry))) {
                struct iattr newattrs = {
                        .ia_ctime = current_time(inode),
                        .ia_size = new_size,
                        .ia_valid = ATTR_SIZE | ATTR_CTIME,
                };

                inode_lock_nested(d_inode(dentry), I_MUTEX_XATTR);
                inode_dio_wait(d_inode(dentry));

                err = reiserfs_setattr(dentry, &newattrs);
                inode_unlock(d_inode(dentry));
        } else
                update_ctime(inode);
out_unlock:
        up_write(&REISERFS_I(inode)->i_xattr_sem);
        dput(dentry);
        return err;
}

/* We need to start a transaction to maintain lock ordering */
int reiserfs_xattr_set(struct inode *inode, const char *name,
                       const void *buffer, size_t buffer_size, int flags)
{

        struct reiserfs_transaction_handle th;
        int error, error2;
        size_t jbegin_count = reiserfs_xattr_nblocks(inode, buffer_size);

        /* Check before we start a transaction and then do nothing. */
        if (!d_really_is_positive(REISERFS_SB(inode->i_sb)->priv_root))
                return -EOPNOTSUPP;

        if (!(flags & XATTR_REPLACE))
                jbegin_count += reiserfs_xattr_jcreate_nblocks(inode);

        reiserfs_write_lock(inode->i_sb);
        error = journal_begin(&th, inode->i_sb, jbegin_count);
        reiserfs_write_unlock(inode->i_sb);
        if (error) {
                return error;
        }

        error = reiserfs_xattr_set_handle(&th, inode, name,
                                          buffer, buffer_size, flags);

        reiserfs_write_lock(inode->i_sb);
        error2 = journal_end(&th);
        reiserfs_write_unlock(inode->i_sb);
        if (error == 0)
                error = error2;

        return error;
}

/*
 * inode->i_mutex: down
 */
int
reiserfs_xattr_get(struct inode *inode, const char *name, void *buffer,
                   size_t buffer_size)
{
        ssize_t err = 0;
        struct dentry *dentry;
        size_t isize;
        size_t file_pos = 0;
        size_t buffer_pos = 0;
        struct page *page;
        __u32 hash = 0;

        if (name == NULL)
                return -EINVAL;

        /*
         * We can't have xattrs attached to v1 items since they don't have
         * generation numbers
         */
        if (get_inode_sd_version(inode) == STAT_DATA_V1)
                return -EOPNOTSUPP;

        /*
         * priv_root needn't be initialized during mount so allow initial
         * lookups to succeed.
         */
        if (!REISERFS_SB(inode->i_sb)->priv_root)
                return 0;

        dentry = xattr_lookup(inode, name, XATTR_REPLACE);
        if (IS_ERR(dentry)) {
                err = PTR_ERR(dentry);
                goto out;
        }

        down_read(&REISERFS_I(inode)->i_xattr_sem);

        isize = i_size_read(d_inode(dentry));

        /* Just return the size needed */
        if (buffer == NULL) {
                err = isize - sizeof(struct reiserfs_xattr_header);
                goto out_unlock;
        }

        if (buffer_size < isize - sizeof(struct reiserfs_xattr_header)) {
                err = -ERANGE;
                goto out_unlock;
        }

        while (file_pos < isize) {
                size_t chunk;
                char *data;
                size_t skip = 0;

                if (isize - file_pos > PAGE_SIZE)
                        chunk = PAGE_SIZE;
                else
                        chunk = isize - file_pos;

                page = reiserfs_get_page(d_inode(dentry), file_pos);
                if (IS_ERR(page)) {
                        err = PTR_ERR(page);
                        goto out_unlock;
                }

                lock_page(page);
                data = page_address(page);
                if (file_pos == 0) {
                        struct reiserfs_xattr_header *rxh =
                            (struct reiserfs_xattr_header *)data;
                        skip = file_pos = sizeof(struct reiserfs_xattr_header);
                        chunk -= skip;
                        /* Magic doesn't match up.. */
                        if (rxh->h_magic != cpu_to_le32(REISERFS_XATTR_MAGIC)) {
                                unlock_page(page);
                                reiserfs_put_page(page);
                                reiserfs_warning(inode->i_sb, "jdm-20001",
                                                 "Invalid magic for xattr (%s) "
                                                 "associated with %k", name,
                                                 INODE_PKEY(inode));
                                err = -EIO;
                                goto out_unlock;
                        }
                        hash = le32_to_cpu(rxh->h_hash);
                }
                memcpy(buffer + buffer_pos, data + skip, chunk);
                unlock_page(page);
                reiserfs_put_page(page);
                file_pos += chunk;
                buffer_pos += chunk;
                skip = 0;
        }
        err = isize - sizeof(struct reiserfs_xattr_header);

        if (xattr_hash(buffer, isize - sizeof(struct reiserfs_xattr_header)) !=
            hash) {
                reiserfs_warning(inode->i_sb, "jdm-20002",
                                 "Invalid hash for xattr (%s) associated "
                                 "with %k", name, INODE_PKEY(inode));
                err = -EIO;
        }

out_unlock:
        up_read(&REISERFS_I(inode)->i_xattr_sem);
        dput(dentry);

out:
        return err;
}

/*
 * In order to implement different sets of xattr operations for each xattr
 * prefix with the generic xattr API, a filesystem should create a
 * null-terminated array of struct xattr_handler (one for each prefix) and
 * hang a pointer to it off of the s_xattr field of the superblock.
 *
 * The generic_fooxattr() functions will use this list to dispatch xattr
 * operations to the correct xattr_handler.
 */
#define for_each_xattr_handler(handlers, handler)               \
                for ((handler) = *(handlers)++;                 \
                        (handler) != NULL;                      \
                        (handler) = *(handlers)++)

/* This is the implementation for the xattr plugin infrastructure */
static inline const struct xattr_handler *
find_xattr_handler_prefix(const struct xattr_handler **handlers,
                           const char *name)
{
        const struct xattr_handler *xah;

        if (!handlers)
                return NULL;

        for_each_xattr_handler(handlers, xah) {
                const char *prefix = xattr_prefix(xah);
                if (strncmp(prefix, name, strlen(prefix)) == 0)
                        break;
        }

        return xah;
}

struct listxattr_buf {
        struct dir_context ctx;
        size_t size;
        size_t pos;
        char *buf;
        struct dentry *dentry;
};

static int listxattr_filler(struct dir_context *ctx, const char *name,
                            int namelen, loff_t offset, u64 ino,
                            unsigned int d_type)
{
        struct listxattr_buf *b =
                container_of(ctx, struct listxattr_buf, ctx);
        size_t size;

        if (name[0] != '.' ||
            (namelen != 1 && (name[1] != '.' || namelen != 2))) {
                const struct xattr_handler *handler;

                handler = find_xattr_handler_prefix(b->dentry->d_sb->s_xattr,
                                                    name);
                if (!handler /* Unsupported xattr name */ ||
                    (handler->list && !handler->list(b->dentry)))
                        return 0;
                size = namelen + 1;
                if (b->buf) {
                        if (b->pos + size > b->size) {
                                b->pos = -ERANGE;
                                return -ERANGE;
                        }
                        memcpy(b->buf + b->pos, name, namelen);
                        b->buf[b->pos + namelen] = 0;
                }
                b->pos += size;
        }
        return 0;
}

/*
 * Inode operation listxattr()
 *
 * We totally ignore the generic listxattr here because it would be stupid
 * not to. Since the xattrs are organized in a directory, we can just
 * readdir to find them.
 */
ssize_t reiserfs_listxattr(struct dentry * dentry, char *buffer, size_t size)
{
        struct dentry *dir;
        int err = 0;
        struct listxattr_buf buf = {
                .ctx.actor = listxattr_filler,
                .dentry = dentry,
                .buf = buffer,
                .size = buffer ? size : 0,
        };

        if (d_really_is_negative(dentry))
                return -EINVAL;

        if (get_inode_sd_version(d_inode(dentry)) == STAT_DATA_V1)
                return -EOPNOTSUPP;

        dir = open_xa_dir(d_inode(dentry), XATTR_REPLACE);
        if (IS_ERR(dir)) {
                err = PTR_ERR(dir);
                if (err == -ENODATA)
                        err = 0;  /* Not an error if there aren't any xattrs */
                goto out;
        }

        inode_lock_nested(d_inode(dir), I_MUTEX_XATTR);
        err = reiserfs_readdir_inode(d_inode(dir), &buf.ctx);
        inode_unlock(d_inode(dir));

        if (!err)
                err = buf.pos;

        dput(dir);
out:
        return err;
}

static int create_privroot(struct dentry *dentry)
{
        int err;
        struct inode *inode = d_inode(dentry->d_parent);

        WARN_ON_ONCE(!inode_is_locked(inode));

        err = xattr_mkdir(inode, dentry, 0700);
        if (err || d_really_is_negative(dentry)) {
                reiserfs_warning(dentry->d_sb, "jdm-20006",
                                 "xattrs/ACLs enabled and couldn't "
                                 "find/create .reiserfs_priv. "
                                 "Failing mount.");
                return -EOPNOTSUPP;
        }

        d_inode(dentry)->i_flags |= S_PRIVATE;
        d_inode(dentry)->i_opflags &= ~IOP_XATTR;
        reiserfs_info(dentry->d_sb, "Created %s - reserved for xattr "
                      "storage.\n", PRIVROOT_NAME);

        return 0;
}

#else
int __init reiserfs_xattr_register_handlers(void) { return 0; }
void reiserfs_xattr_unregister_handlers(void) {}
static int create_privroot(struct dentry *dentry) { return 0; }
#endif

/* Actual operations that are exported to VFS-land */
const struct xattr_handler *reiserfs_xattr_handlers[] = {
#ifdef CONFIG_REISERFS_FS_XATTR
        &reiserfs_xattr_user_handler,
        &reiserfs_xattr_trusted_handler,
#endif
#ifdef CONFIG_REISERFS_FS_SECURITY
        &reiserfs_xattr_security_handler,
#endif
#ifdef CONFIG_REISERFS_FS_POSIX_ACL
        &posix_acl_access_xattr_handler,
        &posix_acl_default_xattr_handler,
#endif
        NULL
};

static int xattr_mount_check(struct super_block *s)
{
        /*
         * We need generation numbers to ensure that the oid mapping is correct
         * v3.5 filesystems don't have them.
         */
        if (old_format_only(s)) {
                if (reiserfs_xattrs_optional(s)) {
                        /*
                         * Old format filesystem, but optional xattrs have
                         * been enabled. Error out.
                         */
                        reiserfs_warning(s, "jdm-2005",
                                         "xattrs/ACLs not supported "
                                         "on pre-v3.6 format filesystems. "
                                         "Failing mount.");
                        return -EOPNOTSUPP;
                }
        }

        return 0;
}

int reiserfs_permission(struct inode *inode, int mask)
{
        /*
         * We don't do permission checks on the internal objects.
         * Permissions are determined by the "owning" object.
         */
        if (IS_PRIVATE(inode))
                return 0;

        return generic_permission(inode, mask);
}

static int xattr_hide_revalidate(struct dentry *dentry, unsigned int flags)
{
        return -EPERM;
}

static const struct dentry_operations xattr_lookup_poison_ops = {
        .d_revalidate = xattr_hide_revalidate,
};

int reiserfs_lookup_privroot(struct super_block *s)
{
        struct dentry *dentry;
        int err = 0;

        /* If we don't have the privroot located yet - go find it */
        inode_lock(d_inode(s->s_root));
        dentry = lookup_one_len(PRIVROOT_NAME, s->s_root,
                                strlen(PRIVROOT_NAME));
        if (!IS_ERR(dentry)) {
                REISERFS_SB(s)->priv_root = dentry;
                d_set_d_op(dentry, &xattr_lookup_poison_ops);
                if (d_really_is_positive(dentry)) {
                        d_inode(dentry)->i_flags |= S_PRIVATE;
                        d_inode(dentry)->i_opflags &= ~IOP_XATTR;
                }
        } else
                err = PTR_ERR(dentry);
        inode_unlock(d_inode(s->s_root));

        return err;
}

/*
 * We need to take a copy of the mount flags since things like
 * MS_RDONLY don't get set until *after* we're called.
 * mount_flags != mount_options
 */
int reiserfs_xattr_init(struct super_block *s, int mount_flags)
{
        int err = 0;
        struct dentry *privroot = REISERFS_SB(s)->priv_root;

        err = xattr_mount_check(s);
        if (err)
                goto error;

        if (d_really_is_negative(privroot) && !(mount_flags & MS_RDONLY)) {
                inode_lock(d_inode(s->s_root));
                err = create_privroot(REISERFS_SB(s)->priv_root);
                inode_unlock(d_inode(s->s_root));
        }

        if (d_really_is_positive(privroot)) {
                inode_lock(d_inode(privroot));
                if (!REISERFS_SB(s)->xattr_root) {
                        struct dentry *dentry;

                        dentry = lookup_one_len(XAROOT_NAME, privroot,
                                                strlen(XAROOT_NAME));
                        if (!IS_ERR(dentry))
                                REISERFS_SB(s)->xattr_root = dentry;
                        else
                                err = PTR_ERR(dentry);
                }
                inode_unlock(d_inode(privroot));
        }

error:
        if (err) {
                clear_bit(REISERFS_XATTRS_USER, &REISERFS_SB(s)->s_mount_opt);
                clear_bit(REISERFS_POSIXACL, &REISERFS_SB(s)->s_mount_opt);
        }

        /* The super_block MS_POSIXACL must mirror the (no)acl mount option. */
        if (reiserfs_posixacl(s))
                s->s_flags |= MS_POSIXACL;
        else
                s->s_flags &= ~MS_POSIXACL;

        return err;
}