Btrfs: fix how we mount subvol=<whatever>

[mirror_ubuntu-artful-kernel.git] / fs / btrfs / super.c

/*
 * Copyright (C) 2007 Oracle.  All rights reserved.
 *
 * This program is free software; you can redistribute it and/or
 * modify it under the terms of the GNU General Public
 * License v2 as published by the Free Software Foundation.
 *
 * This program is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * General Public License for more details.
 *
 * You should have received a copy of the GNU General Public
 * License along with this program; if not, write to the
 * Free Software Foundation, Inc., 59 Temple Place - Suite 330,
 * Boston, MA 021110-1307, USA.
 */

#include <linux/blkdev.h>
#include <linux/module.h>
#include <linux/buffer_head.h>
#include <linux/fs.h>
#include <linux/pagemap.h>
#include <linux/highmem.h>
#include <linux/time.h>
#include <linux/init.h>
#include <linux/seq_file.h>
#include <linux/string.h>
#include <linux/backing-dev.h>
#include <linux/mount.h>
#include <linux/mpage.h>
#include <linux/swap.h>
#include <linux/writeback.h>
#include <linux/statfs.h>
#include <linux/compat.h>
#include <linux/parser.h>
#include <linux/ctype.h>
#include <linux/namei.h>
#include <linux/miscdevice.h>
#include <linux/magic.h>
#include <linux/slab.h>
#include <linux/cleancache.h>
#include <linux/mnt_namespace.h>
#include "compat.h"
#include "delayed-inode.h"
#include "ctree.h"
#include "disk-io.h"
#include "transaction.h"
#include "btrfs_inode.h"
#include "ioctl.h"
#include "print-tree.h"
#include "xattr.h"
#include "volumes.h"
#include "version.h"
#include "export.h"
#include "compression.h"

#define CREATE_TRACE_POINTS
#include <trace/events/btrfs.h>

static const struct super_operations btrfs_super_ops;
static struct file_system_type btrfs_fs_type;

static const char *btrfs_decode_error(struct btrfs_fs_info *fs_info, int errno,
                                      char nbuf[16])
{
        char *errstr = NULL;

        switch (errno) {
        case -EIO:
                errstr = "IO failure";
                break;
        case -ENOMEM:
                errstr = "Out of memory";
                break;
        case -EROFS:
                errstr = "Readonly filesystem";
                break;
        default:
                if (nbuf) {
                        if (snprintf(nbuf, 16, "error %d", -errno) >= 0)
                                errstr = nbuf;
                }
                break;
        }

        return errstr;
}

static void __save_error_info(struct btrfs_fs_info *fs_info)
{
        /*
         * today we only save the error info into ram.  Long term we'll
         * also send it down to the disk
         */
        fs_info->fs_state = BTRFS_SUPER_FLAG_ERROR;
}

/* NOTE:
 *      We move write_super stuff at umount in order to avoid deadlock
 *      for umount hold all lock.
 */
static void save_error_info(struct btrfs_fs_info *fs_info)
{
        __save_error_info(fs_info);
}

/* btrfs handle error by forcing the filesystem readonly */
static void btrfs_handle_error(struct btrfs_fs_info *fs_info)
{
        struct super_block *sb = fs_info->sb;

        if (sb->s_flags & MS_RDONLY)
                return;

        if (fs_info->fs_state & BTRFS_SUPER_FLAG_ERROR) {
                sb->s_flags |= MS_RDONLY;
                printk(KERN_INFO "btrfs is forced readonly\n");
        }
}

/*
 * __btrfs_std_error decodes expected errors from the caller and
 * invokes the approciate error response.
 */
void __btrfs_std_error(struct btrfs_fs_info *fs_info, const char *function,
                     unsigned int line, int errno)
{
        struct super_block *sb = fs_info->sb;
        char nbuf[16];
        const char *errstr;

        /*
         * Special case: if the error is EROFS, and we're already
         * under MS_RDONLY, then it is safe here.
         */
        if (errno == -EROFS && (sb->s_flags & MS_RDONLY))
                return;

        errstr = btrfs_decode_error(fs_info, errno, nbuf);
        printk(KERN_CRIT "BTRFS error (device %s) in %s:%d: %s\n",
                sb->s_id, function, line, errstr);
        save_error_info(fs_info);

        btrfs_handle_error(fs_info);
}

static void btrfs_put_super(struct super_block *sb)
{
        struct btrfs_root *root = btrfs_sb(sb);
        int ret;

        ret = close_ctree(root);
        sb->s_fs_info = NULL;

        (void)ret; /* FIXME: need to fix VFS to return error? */
}

enum {
        Opt_degraded, Opt_subvol, Opt_subvolid, Opt_device, Opt_nodatasum,
        Opt_nodatacow, Opt_max_inline, Opt_alloc_start, Opt_nobarrier, Opt_ssd,
        Opt_nossd, Opt_ssd_spread, Opt_thread_pool, Opt_noacl, Opt_compress,
        Opt_compress_type, Opt_compress_force, Opt_compress_force_type,
        Opt_notreelog, Opt_ratio, Opt_flushoncommit, Opt_discard,
        Opt_space_cache, Opt_clear_cache, Opt_user_subvol_rm_allowed,
        Opt_enospc_debug, Opt_subvolrootid, Opt_defrag,
        Opt_inode_cache, Opt_err,
};

static match_table_t tokens = {
        {Opt_degraded, "degraded"},
        {Opt_subvol, "subvol=%s"},
        {Opt_subvolid, "subvolid=%d"},
        {Opt_device, "device=%s"},
        {Opt_nodatasum, "nodatasum"},
        {Opt_nodatacow, "nodatacow"},
        {Opt_nobarrier, "nobarrier"},
        {Opt_max_inline, "max_inline=%s"},
        {Opt_alloc_start, "alloc_start=%s"},
        {Opt_thread_pool, "thread_pool=%d"},
        {Opt_compress, "compress"},
        {Opt_compress_type, "compress=%s"},
        {Opt_compress_force, "compress-force"},
        {Opt_compress_force_type, "compress-force=%s"},
        {Opt_ssd, "ssd"},
        {Opt_ssd_spread, "ssd_spread"},
        {Opt_nossd, "nossd"},
        {Opt_noacl, "noacl"},
        {Opt_notreelog, "notreelog"},
        {Opt_flushoncommit, "flushoncommit"},
        {Opt_ratio, "metadata_ratio=%d"},
        {Opt_discard, "discard"},
        {Opt_space_cache, "space_cache"},
        {Opt_clear_cache, "clear_cache"},
        {Opt_user_subvol_rm_allowed, "user_subvol_rm_allowed"},
        {Opt_enospc_debug, "enospc_debug"},
        {Opt_subvolrootid, "subvolrootid=%d"},
        {Opt_defrag, "autodefrag"},
        {Opt_inode_cache, "inode_cache"},
        {Opt_err, NULL},
};

/*
 * Regular mount options parser.  Everything that is needed only when
 * reading in a new superblock is parsed here.
 */
int btrfs_parse_options(struct btrfs_root *root, char *options)
{
        struct btrfs_fs_info *info = root->fs_info;
        substring_t args[MAX_OPT_ARGS];
        char *p, *num, *orig;
        int intarg;
        int ret = 0;
        char *compress_type;
        bool compress_force = false;

        if (!options)
                return 0;

        /*
         * strsep changes the string, duplicate it because parse_options
         * gets called twice
         */
        options = kstrdup(options, GFP_NOFS);
        if (!options)
                return -ENOMEM;

        orig = options;

        while ((p = strsep(&options, ",")) != NULL) {
                int token;
                if (!*p)
                        continue;

                token = match_token(p, tokens, args);
                switch (token) {
                case Opt_degraded:
                        printk(KERN_INFO "btrfs: allowing degraded mounts\n");
                        btrfs_set_opt(info->mount_opt, DEGRADED);
                        break;
                case Opt_subvol:
                case Opt_subvolid:
                case Opt_subvolrootid:
                case Opt_device:
                        /*
                         * These are parsed by btrfs_parse_early_options
                         * and can be happily ignored here.
                         */
                        break;
                case Opt_nodatasum:
                        printk(KERN_INFO "btrfs: setting nodatasum\n");
                        btrfs_set_opt(info->mount_opt, NODATASUM);
                        break;
                case Opt_nodatacow:
                        printk(KERN_INFO "btrfs: setting nodatacow\n");
                        btrfs_set_opt(info->mount_opt, NODATACOW);
                        btrfs_set_opt(info->mount_opt, NODATASUM);
                        break;
                case Opt_compress_force:
                case Opt_compress_force_type:
                        compress_force = true;
                case Opt_compress:
                case Opt_compress_type:
                        if (token == Opt_compress ||
                            token == Opt_compress_force ||
                            strcmp(args[0].from, "zlib") == 0) {
                                compress_type = "zlib";
                                info->compress_type = BTRFS_COMPRESS_ZLIB;
                        } else if (strcmp(args[0].from, "lzo") == 0) {
                                compress_type = "lzo";
                                info->compress_type = BTRFS_COMPRESS_LZO;
                        } else {
                                ret = -EINVAL;
                                goto out;
                        }

                        btrfs_set_opt(info->mount_opt, COMPRESS);
                        if (compress_force) {
                                btrfs_set_opt(info->mount_opt, FORCE_COMPRESS);
                                pr_info("btrfs: force %s compression\n",
                                        compress_type);
                        } else
                                pr_info("btrfs: use %s compression\n",
                                        compress_type);
                        break;
                case Opt_ssd:
                        printk(KERN_INFO "btrfs: use ssd allocation scheme\n");
                        btrfs_set_opt(info->mount_opt, SSD);
                        break;
                case Opt_ssd_spread:
                        printk(KERN_INFO "btrfs: use spread ssd "
                               "allocation scheme\n");
                        btrfs_set_opt(info->mount_opt, SSD);
                        btrfs_set_opt(info->mount_opt, SSD_SPREAD);
                        break;
                case Opt_nossd:
                        printk(KERN_INFO "btrfs: not using ssd allocation "
                               "scheme\n");
                        btrfs_set_opt(info->mount_opt, NOSSD);
                        btrfs_clear_opt(info->mount_opt, SSD);
                        btrfs_clear_opt(info->mount_opt, SSD_SPREAD);
                        break;
                case Opt_nobarrier:
                        printk(KERN_INFO "btrfs: turning off barriers\n");
                        btrfs_set_opt(info->mount_opt, NOBARRIER);
                        break;
                case Opt_thread_pool:
                        intarg = 0;
                        match_int(&args[0], &intarg);
                        if (intarg) {
                                info->thread_pool_size = intarg;
                                printk(KERN_INFO "btrfs: thread pool %d\n",
                                       info->thread_pool_size);
                        }
                        break;
                case Opt_max_inline:
                        num = match_strdup(&args[0]);
                        if (num) {
                                info->max_inline = memparse(num, NULL);
                                kfree(num);

                                if (info->max_inline) {
                                        info->max_inline = max_t(u64,
                                                info->max_inline,
                                                root->sectorsize);
                                }
                                printk(KERN_INFO "btrfs: max_inline at %llu\n",
                                        (unsigned long long)info->max_inline);
                        }
                        break;
                case Opt_alloc_start:
                        num = match_strdup(&args[0]);
                        if (num) {
                                info->alloc_start = memparse(num, NULL);
                                kfree(num);
                                printk(KERN_INFO
                                        "btrfs: allocations start at %llu\n",
                                        (unsigned long long)info->alloc_start);
                        }
                        break;
                case Opt_noacl:
                        root->fs_info->sb->s_flags &= ~MS_POSIXACL;
                        break;
                case Opt_notreelog:
                        printk(KERN_INFO "btrfs: disabling tree log\n");
                        btrfs_set_opt(info->mount_opt, NOTREELOG);
                        break;
                case Opt_flushoncommit:
                        printk(KERN_INFO "btrfs: turning on flush-on-commit\n");
                        btrfs_set_opt(info->mount_opt, FLUSHONCOMMIT);
                        break;
                case Opt_ratio:
                        intarg = 0;
                        match_int(&args[0], &intarg);
                        if (intarg) {
                                info->metadata_ratio = intarg;
                                printk(KERN_INFO "btrfs: metadata ratio %d\n",
                                       info->metadata_ratio);
                        }
                        break;
                case Opt_discard:
                        btrfs_set_opt(info->mount_opt, DISCARD);
                        break;
                case Opt_space_cache:
                        printk(KERN_INFO "btrfs: enabling disk space caching\n");
                        btrfs_set_opt(info->mount_opt, SPACE_CACHE);
                        break;
                case Opt_inode_cache:
                        printk(KERN_INFO "btrfs: enabling inode map caching\n");
                        btrfs_set_opt(info->mount_opt, INODE_MAP_CACHE);
                        break;
                case Opt_clear_cache:
                        printk(KERN_INFO "btrfs: force clearing of disk cache\n");
                        btrfs_set_opt(info->mount_opt, CLEAR_CACHE);
                        break;
                case Opt_user_subvol_rm_allowed:
                        btrfs_set_opt(info->mount_opt, USER_SUBVOL_RM_ALLOWED);
                        break;
                case Opt_enospc_debug:
                        btrfs_set_opt(info->mount_opt, ENOSPC_DEBUG);
                        break;
                case Opt_defrag:
                        printk(KERN_INFO "btrfs: enabling auto defrag");
                        btrfs_set_opt(info->mount_opt, AUTO_DEFRAG);
                        break;
                case Opt_err:
                        printk(KERN_INFO "btrfs: unrecognized mount option "
                               "'%s'\n", p);
                        ret = -EINVAL;
                        goto out;
                default:
                        break;
                }
        }
out:
        kfree(orig);
        return ret;
}

/*
 * Parse mount options that are required early in the mount process.
 *
 * All other options will be parsed on much later in the mount process and
 * only when we need to allocate a new super block.
 */
static int btrfs_parse_early_options(const char *options, fmode_t flags,
                void *holder, char **subvol_name, u64 *subvol_objectid,
                u64 *subvol_rootid, struct btrfs_fs_devices **fs_devices)
{
        substring_t args[MAX_OPT_ARGS];
        char *opts, *orig, *p;
        int error = 0;
        int intarg;

        if (!options)
                return 0;

        /*
         * strsep changes the string, duplicate it because parse_options
         * gets called twice
         */
        opts = kstrdup(options, GFP_KERNEL);
        if (!opts)
                return -ENOMEM;
        orig = opts;

        while ((p = strsep(&opts, ",")) != NULL) {
                int token;
                if (!*p)
                        continue;

                token = match_token(p, tokens, args);
                switch (token) {
                case Opt_subvol:
                        *subvol_name = match_strdup(&args[0]);
                        break;
                case Opt_subvolid:
                        intarg = 0;
                        error = match_int(&args[0], &intarg);
                        if (!error) {
                                /* we want the original fs_tree */
                                if (!intarg)
                                        *subvol_objectid =
                                                BTRFS_FS_TREE_OBJECTID;
                                else
                                        *subvol_objectid = intarg;
                        }
                        break;
                case Opt_subvolrootid:
                        intarg = 0;
                        error = match_int(&args[0], &intarg);
                        if (!error) {
                                /* we want the original fs_tree */
                                if (!intarg)
                                        *subvol_rootid =
                                                BTRFS_FS_TREE_OBJECTID;
                                else
                                        *subvol_rootid = intarg;
                        }
                        break;
                case Opt_device:
                        error = btrfs_scan_one_device(match_strdup(&args[0]),
                                        flags, holder, fs_devices);
                        if (error)
                                goto out;
                        break;
                default:
                        break;
                }
        }

out:
        kfree(orig);
        return error;
}

static struct dentry *get_default_root(struct super_block *sb,
                                       u64 subvol_objectid)
{
        struct btrfs_root *root = sb->s_fs_info;
        struct btrfs_root *new_root;
        struct btrfs_dir_item *di;
        struct btrfs_path *path;
        struct btrfs_key location;
        struct inode *inode;
        u64 dir_id;
        int new = 0;

        /*
         * We have a specific subvol we want to mount, just setup location and
         * go look up the root.
         */
        if (subvol_objectid) {
                location.objectid = subvol_objectid;
                location.type = BTRFS_ROOT_ITEM_KEY;
                location.offset = (u64)-1;
                goto find_root;
        }

        path = btrfs_alloc_path();
        if (!path)
                return ERR_PTR(-ENOMEM);
        path->leave_spinning = 1;

        /*
         * Find the "default" dir item which points to the root item that we
         * will mount by default if we haven't been given a specific subvolume
         * to mount.
         */
        dir_id = btrfs_super_root_dir(&root->fs_info->super_copy);
        di = btrfs_lookup_dir_item(NULL, root, path, dir_id, "default", 7, 0);
        if (IS_ERR(di)) {
                btrfs_free_path(path);
                return ERR_CAST(di);
        }
        if (!di) {
                /*
                 * Ok the default dir item isn't there.  This is weird since
                 * it's always been there, but don't freak out, just try and
                 * mount to root most subvolume.
                 */
                btrfs_free_path(path);
                dir_id = BTRFS_FIRST_FREE_OBJECTID;
                new_root = root->fs_info->fs_root;
                goto setup_root;
        }

        btrfs_dir_item_key_to_cpu(path->nodes[0], di, &location);
        btrfs_free_path(path);

find_root:
        new_root = btrfs_read_fs_root_no_name(root->fs_info, &location);
        if (IS_ERR(new_root))
                return ERR_CAST(new_root);

        if (btrfs_root_refs(&new_root->root_item) == 0)
                return ERR_PTR(-ENOENT);

        dir_id = btrfs_root_dirid(&new_root->root_item);
setup_root:
        location.objectid = dir_id;
        location.type = BTRFS_INODE_ITEM_KEY;
        location.offset = 0;

        inode = btrfs_iget(sb, &location, new_root, &new);
        if (IS_ERR(inode))
                return ERR_CAST(inode);

        /*
         * If we're just mounting the root most subvol put the inode and return
         * a reference to the dentry.  We will have already gotten a reference
         * to the inode in btrfs_fill_super so we're good to go.
         */
        if (!new && sb->s_root->d_inode == inode) {
                iput(inode);
                return dget(sb->s_root);
        }

        return d_obtain_alias(inode);
}

static int btrfs_fill_super(struct super_block *sb,
                            struct btrfs_fs_devices *fs_devices,
                            void *data, int silent)
{
        struct inode *inode;
        struct dentry *root_dentry;
        struct btrfs_root *tree_root;
        struct btrfs_key key;
        int err;

        sb->s_maxbytes = MAX_LFS_FILESIZE;
        sb->s_magic = BTRFS_SUPER_MAGIC;
        sb->s_op = &btrfs_super_ops;
        sb->s_d_op = &btrfs_dentry_operations;
        sb->s_export_op = &btrfs_export_ops;
        sb->s_xattr = btrfs_xattr_handlers;
        sb->s_time_gran = 1;
#ifdef CONFIG_BTRFS_FS_POSIX_ACL
        sb->s_flags |= MS_POSIXACL;
#endif

        tree_root = open_ctree(sb, fs_devices, (char *)data);

        if (IS_ERR(tree_root)) {
                printk("btrfs: open_ctree failed\n");
                return PTR_ERR(tree_root);
        }
        sb->s_fs_info = tree_root;

        key.objectid = BTRFS_FIRST_FREE_OBJECTID;
        key.type = BTRFS_INODE_ITEM_KEY;
        key.offset = 0;
        inode = btrfs_iget(sb, &key, tree_root->fs_info->fs_root, NULL);
        if (IS_ERR(inode)) {
                err = PTR_ERR(inode);
                goto fail_close;
        }

        root_dentry = d_alloc_root(inode);
        if (!root_dentry) {
                iput(inode);
                err = -ENOMEM;
                goto fail_close;
        }

        sb->s_root = root_dentry;

        save_mount_options(sb, data);
        cleancache_init_fs(sb);
        return 0;

fail_close:
        close_ctree(tree_root);
        return err;
}

int btrfs_sync_fs(struct super_block *sb, int wait)
{
        struct btrfs_trans_handle *trans;
        struct btrfs_root *root = btrfs_sb(sb);
        int ret;

        trace_btrfs_sync_fs(wait);

        if (!wait) {
                filemap_flush(root->fs_info->btree_inode->i_mapping);
                return 0;
        }

        btrfs_start_delalloc_inodes(root, 0);
        btrfs_wait_ordered_extents(root, 0, 0);

        trans = btrfs_start_transaction(root, 0);
        if (IS_ERR(trans))
                return PTR_ERR(trans);
        ret = btrfs_commit_transaction(trans, root);
        return ret;
}

static int btrfs_show_options(struct seq_file *seq, struct vfsmount *vfs)
{
        struct btrfs_root *root = btrfs_sb(vfs->mnt_sb);
        struct btrfs_fs_info *info = root->fs_info;
        char *compress_type;

        if (btrfs_test_opt(root, DEGRADED))
                seq_puts(seq, ",degraded");
        if (btrfs_test_opt(root, NODATASUM))
                seq_puts(seq, ",nodatasum");
        if (btrfs_test_opt(root, NODATACOW))
                seq_puts(seq, ",nodatacow");
        if (btrfs_test_opt(root, NOBARRIER))
                seq_puts(seq, ",nobarrier");
        if (info->max_inline != 8192 * 1024)
                seq_printf(seq, ",max_inline=%llu",
                           (unsigned long long)info->max_inline);
        if (info->alloc_start != 0)
                seq_printf(seq, ",alloc_start=%llu",
                           (unsigned long long)info->alloc_start);
        if (info->thread_pool_size !=  min_t(unsigned long,
                                             num_online_cpus() + 2, 8))
                seq_printf(seq, ",thread_pool=%d", info->thread_pool_size);
        if (btrfs_test_opt(root, COMPRESS)) {
                if (info->compress_type == BTRFS_COMPRESS_ZLIB)
                        compress_type = "zlib";
                else
                        compress_type = "lzo";
                if (btrfs_test_opt(root, FORCE_COMPRESS))
                        seq_printf(seq, ",compress-force=%s", compress_type);
                else
                        seq_printf(seq, ",compress=%s", compress_type);
        }
        if (btrfs_test_opt(root, NOSSD))
                seq_puts(seq, ",nossd");
        if (btrfs_test_opt(root, SSD_SPREAD))
                seq_puts(seq, ",ssd_spread");
        else if (btrfs_test_opt(root, SSD))
                seq_puts(seq, ",ssd");
        if (btrfs_test_opt(root, NOTREELOG))
                seq_puts(seq, ",notreelog");
        if (btrfs_test_opt(root, FLUSHONCOMMIT))
                seq_puts(seq, ",flushoncommit");
        if (btrfs_test_opt(root, DISCARD))
                seq_puts(seq, ",discard");
        if (!(root->fs_info->sb->s_flags & MS_POSIXACL))
                seq_puts(seq, ",noacl");
        if (btrfs_test_opt(root, SPACE_CACHE))
                seq_puts(seq, ",space_cache");
        if (btrfs_test_opt(root, CLEAR_CACHE))
                seq_puts(seq, ",clear_cache");
        if (btrfs_test_opt(root, USER_SUBVOL_RM_ALLOWED))
                seq_puts(seq, ",user_subvol_rm_allowed");
        if (btrfs_test_opt(root, ENOSPC_DEBUG))
                seq_puts(seq, ",enospc_debug");
        if (btrfs_test_opt(root, AUTO_DEFRAG))
                seq_puts(seq, ",autodefrag");
        if (btrfs_test_opt(root, INODE_MAP_CACHE))
                seq_puts(seq, ",inode_cache");
        return 0;
}

static int btrfs_test_super(struct super_block *s, void *data)
{
        struct btrfs_root *test_root = data;
        struct btrfs_root *root = btrfs_sb(s);

        /*
         * If this super block is going away, return false as it
         * can't match as an existing super block.
         */
        if (!atomic_read(&s->s_active))
                return 0;
        return root->fs_info->fs_devices == test_root->fs_info->fs_devices;
}

static int btrfs_set_super(struct super_block *s, void *data)
{
        s->s_fs_info = data;

        return set_anon_super(s, data);
}

/*
 * This will strip out the subvol=%s argument for an argument string and add
 * subvolid=0 to make sure we get the actual tree root for path walking to the
 * subvol we want.
 */
static char *setup_root_args(char *args)
{
        unsigned copied = 0;
        unsigned len = strlen(args) + 2;
        char *pos;
        char *ret;

        /*
         * We need the same args as before, but minus
         *
         * subvol=a
         *
         * and add
         *
         * subvolid=0
         *
         * which is a difference of 2 characters, so we allocate strlen(args) +
         * 2 characters.
         */
        ret = kzalloc(len * sizeof(char), GFP_NOFS);
        if (!ret)
                return NULL;
        pos = strstr(args, "subvol=");

        /* This shouldn't happen, but just in case.. */
        if (!pos) {
                kfree(ret);
                return NULL;
        }

        /*
         * The subvol=<> arg is not at the front of the string, copy everybody
         * up to that into ret.
         */
        if (pos != args) {
                *pos = '\0';
                strcpy(ret, args);
                copied += strlen(args);
                pos++;
        }

        strncpy(ret + copied, "subvolid=0", len - copied);

        /* Length of subvolid=0 */
        copied += 10;

        /*
         * If there is no , after the subvol= option then we know there's no
         * other options and we can just return.
         */
        pos = strchr(pos, ',');
        if (!pos)
                return ret;

        /* Copy the rest of the arguments into our buffer */
        strncpy(ret + copied, pos, len - copied);
        copied += strlen(pos);

        return ret;
}

static struct dentry *mount_subvol(const char *subvol_name, int flags,
                                   const char *device_name, char *data)
{
        struct super_block *s;
        struct dentry *root;
        struct vfsmount *mnt;
        struct mnt_namespace *ns_private;
        char *newargs;
        struct path path;
        int error;

        newargs = setup_root_args(data);
        if (!newargs)
                return ERR_PTR(-ENOMEM);
        mnt = vfs_kern_mount(&btrfs_fs_type, flags, device_name,
                             newargs);
        kfree(newargs);
        if (IS_ERR(mnt))
                return ERR_CAST(mnt);

        ns_private = create_mnt_ns(mnt);
        if (IS_ERR(ns_private)) {
                mntput(mnt);
                return ERR_CAST(ns_private);
        }

        /*
         * This will trigger the automount of the subvol so we can just
         * drop the mnt we have here and return the dentry that we
         * found.
         */
        error = vfs_path_lookup(mnt->mnt_root, mnt, subvol_name,
                                LOOKUP_FOLLOW, &path);
        put_mnt_ns(ns_private);
        if (error)
                return ERR_PTR(error);

        /* Get a ref to the sb and the dentry we found and return it */
        s = path.mnt->mnt_sb;
        atomic_inc(&s->s_active);
        root = dget(path.dentry);
        path_put(&path);
        down_write(&s->s_umount);

        return root;
}

/*
 * Find a superblock for the given device / mount point.
 *
 * Note:  This is based on get_sb_bdev from fs/super.c with a few additions
 *        for multiple device setup.  Make sure to keep it in sync.
 */
static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
                const char *device_name, void *data)
{
        struct block_device *bdev = NULL;
        struct super_block *s;
        struct dentry *root;
        struct btrfs_fs_devices *fs_devices = NULL;
        struct btrfs_root *tree_root = NULL;
        struct btrfs_fs_info *fs_info = NULL;
        fmode_t mode = FMODE_READ;
        char *subvol_name = NULL;
        u64 subvol_objectid = 0;
        u64 subvol_rootid = 0;
        int error = 0;

        if (!(flags & MS_RDONLY))
                mode |= FMODE_WRITE;

        error = btrfs_parse_early_options(data, mode, fs_type,
                                          &subvol_name, &subvol_objectid,
                                          &subvol_rootid, &fs_devices);
        if (error)
                return ERR_PTR(error);

        if (subvol_name) {
                root = mount_subvol(subvol_name, flags, device_name, data);
                kfree(subvol_name);
                return root;
        }

        error = btrfs_scan_one_device(device_name, mode, fs_type, &fs_devices);
        if (error)
                return ERR_PTR(error);

        error = btrfs_open_devices(fs_devices, mode, fs_type);
        if (error)
                return ERR_PTR(error);

        if (!(flags & MS_RDONLY) && fs_devices->rw_devices == 0) {
                error = -EACCES;
                goto error_close_devices;
        }

        /*
         * Setup a dummy root and fs_info for test/set super.  This is because
         * we don't actually fill this stuff out until open_ctree, but we need
         * it for searching for existing supers, so this lets us do that and
         * then open_ctree will properly initialize everything later.
         */
        fs_info = kzalloc(sizeof(struct btrfs_fs_info), GFP_NOFS);
        tree_root = kzalloc(sizeof(struct btrfs_root), GFP_NOFS);
        if (!fs_info || !tree_root) {
                error = -ENOMEM;
                goto error_close_devices;
        }
        fs_info->tree_root = tree_root;
        fs_info->fs_devices = fs_devices;
        tree_root->fs_info = fs_info;

        bdev = fs_devices->latest_bdev;
        s = sget(fs_type, btrfs_test_super, btrfs_set_super, tree_root);
        if (IS_ERR(s)) {
                error = PTR_ERR(s);
                goto error_close_devices;
        }

        if (s->s_root) {
                if ((flags ^ s->s_flags) & MS_RDONLY) {
                        deactivate_locked_super(s);
                        return ERR_PTR(-EBUSY);
                }

                btrfs_close_devices(fs_devices);
                kfree(fs_info);
                kfree(tree_root);
        } else {
                char b[BDEVNAME_SIZE];

                s->s_flags = flags | MS_NOSEC;
                strlcpy(s->s_id, bdevname(bdev, b), sizeof(s->s_id));
                error = btrfs_fill_super(s, fs_devices, data,
                                         flags & MS_SILENT ? 1 : 0);
                if (error) {
                        deactivate_locked_super(s);
                        return ERR_PTR(error);
                }

                btrfs_sb(s)->fs_info->bdev_holder = fs_type;
                s->s_flags |= MS_ACTIVE;
        }

        root = get_default_root(s, subvol_objectid);
        if (IS_ERR(root)) {
                deactivate_locked_super(s);
                return root;
        }

        return root;

error_close_devices:
        btrfs_close_devices(fs_devices);
        kfree(fs_info);
        kfree(tree_root);
        return ERR_PTR(error);
}

static int btrfs_remount(struct super_block *sb, int *flags, char *data)
{
        struct btrfs_root *root = btrfs_sb(sb);
        int ret;

        ret = btrfs_parse_options(root, data);
        if (ret)
                return -EINVAL;

        if ((*flags & MS_RDONLY) == (sb->s_flags & MS_RDONLY))
                return 0;

        if (*flags & MS_RDONLY) {
                sb->s_flags |= MS_RDONLY;

                ret =  btrfs_commit_super(root);
                WARN_ON(ret);
        } else {
                if (root->fs_info->fs_devices->rw_devices == 0)
                        return -EACCES;

                if (btrfs_super_log_root(&root->fs_info->super_copy) != 0)
                        return -EINVAL;

                ret = btrfs_cleanup_fs_roots(root->fs_info);
                WARN_ON(ret);

                /* recover relocation */
                ret = btrfs_recover_relocation(root);
                WARN_ON(ret);

                sb->s_flags &= ~MS_RDONLY;
        }

        return 0;
}

/* Used to sort the devices by max_avail(descending sort) */
static int btrfs_cmp_device_free_bytes(const void *dev_info1,
                                       const void *dev_info2)
{
        if (((struct btrfs_device_info *)dev_info1)->max_avail >
            ((struct btrfs_device_info *)dev_info2)->max_avail)
                return -1;
        else if (((struct btrfs_device_info *)dev_info1)->max_avail <
                 ((struct btrfs_device_info *)dev_info2)->max_avail)
                return 1;
        else
        return 0;
}

/*
 * sort the devices by max_avail, in which max free extent size of each device
 * is stored.(Descending Sort)
 */
static inline void btrfs_descending_sort_devices(
                                        struct btrfs_device_info *devices,
                                        size_t nr_devices)
{
        sort(devices, nr_devices, sizeof(struct btrfs_device_info),
             btrfs_cmp_device_free_bytes, NULL);
}

/*
 * The helper to calc the free space on the devices that can be used to store
 * file data.
 */
static int btrfs_calc_avail_data_space(struct btrfs_root *root, u64 *free_bytes)
{
        struct btrfs_fs_info *fs_info = root->fs_info;
        struct btrfs_device_info *devices_info;
        struct btrfs_fs_devices *fs_devices = fs_info->fs_devices;
        struct btrfs_device *device;
        u64 skip_space;
        u64 type;
        u64 avail_space;
        u64 used_space;
        u64 min_stripe_size;
        int min_stripes = 1;
        int i = 0, nr_devices;
        int ret;

        nr_devices = fs_info->fs_devices->rw_devices;
        BUG_ON(!nr_devices);

        devices_info = kmalloc(sizeof(*devices_info) * nr_devices,
                               GFP_NOFS);
        if (!devices_info)
                return -ENOMEM;

        /* calc min stripe number for data space alloction */
        type = btrfs_get_alloc_profile(root, 1);
        if (type & BTRFS_BLOCK_GROUP_RAID0)
                min_stripes = 2;
        else if (type & BTRFS_BLOCK_GROUP_RAID1)
                min_stripes = 2;
        else if (type & BTRFS_BLOCK_GROUP_RAID10)
                min_stripes = 4;

        if (type & BTRFS_BLOCK_GROUP_DUP)
                min_stripe_size = 2 * BTRFS_STRIPE_LEN;
        else
                min_stripe_size = BTRFS_STRIPE_LEN;

        list_for_each_entry(device, &fs_devices->alloc_list, dev_alloc_list) {
                if (!device->in_fs_metadata)
                        continue;

                avail_space = device->total_bytes - device->bytes_used;

                /* align with stripe_len */
                do_div(avail_space, BTRFS_STRIPE_LEN);
                avail_space *= BTRFS_STRIPE_LEN;

                /*
                 * In order to avoid overwritting the superblock on the drive,
                 * btrfs starts at an offset of at least 1MB when doing chunk
                 * allocation.
                 */
                skip_space = 1024 * 1024;

                /* user can set the offset in fs_info->alloc_start. */
                if (fs_info->alloc_start + BTRFS_STRIPE_LEN <=
                    device->total_bytes)
                        skip_space = max(fs_info->alloc_start, skip_space);

                /*
                 * btrfs can not use the free space in [0, skip_space - 1],
                 * we must subtract it from the total. In order to implement
                 * it, we account the used space in this range first.
                 */
                ret = btrfs_account_dev_extents_size(device, 0, skip_space - 1,
                                                     &used_space);
                if (ret) {
                        kfree(devices_info);
                        return ret;
                }

                /* calc the free space in [0, skip_space - 1] */
                skip_space -= used_space;

                /*
                 * we can use the free space in [0, skip_space - 1], subtract
                 * it from the total.
                 */
                if (avail_space && avail_space >= skip_space)
                        avail_space -= skip_space;
                else
                        avail_space = 0;

                if (avail_space < min_stripe_size)
                        continue;

                devices_info[i].dev = device;
                devices_info[i].max_avail = avail_space;

                i++;
        }

        nr_devices = i;

        btrfs_descending_sort_devices(devices_info, nr_devices);

        i = nr_devices - 1;
        avail_space = 0;
        while (nr_devices >= min_stripes) {
                if (devices_info[i].max_avail >= min_stripe_size) {
                        int j;
                        u64 alloc_size;

                        avail_space += devices_info[i].max_avail * min_stripes;
                        alloc_size = devices_info[i].max_avail;
                        for (j = i + 1 - min_stripes; j <= i; j++)
                                devices_info[j].max_avail -= alloc_size;
                }
                i--;
                nr_devices--;
        }

        kfree(devices_info);
        *free_bytes = avail_space;
        return 0;
}

static int btrfs_statfs(struct dentry *dentry, struct kstatfs *buf)
{
        struct btrfs_root *root = btrfs_sb(dentry->d_sb);
        struct btrfs_super_block *disk_super = &root->fs_info->super_copy;
        struct list_head *head = &root->fs_info->space_info;
        struct btrfs_space_info *found;
        u64 total_used = 0;
        u64 total_free_data = 0;
        int bits = dentry->d_sb->s_blocksize_bits;
        __be32 *fsid = (__be32 *)root->fs_info->fsid;
        int ret;

        /* holding chunk_muext to avoid allocating new chunks */
        mutex_lock(&root->fs_info->chunk_mutex);
        rcu_read_lock();
        list_for_each_entry_rcu(found, head, list) {
                if (found->flags & BTRFS_BLOCK_GROUP_DATA) {
                        total_free_data += found->disk_total - found->disk_used;
                        total_free_data -=
                                btrfs_account_ro_block_groups_free_space(found);
                }

                total_used += found->disk_used;
        }
        rcu_read_unlock();

        buf->f_namelen = BTRFS_NAME_LEN;
        buf->f_blocks = btrfs_super_total_bytes(disk_super) >> bits;
        buf->f_bfree = buf->f_blocks - (total_used >> bits);
        buf->f_bsize = dentry->d_sb->s_blocksize;
        buf->f_type = BTRFS_SUPER_MAGIC;
        buf->f_bavail = total_free_data;
        ret = btrfs_calc_avail_data_space(root, &total_free_data);
        if (ret) {
                mutex_unlock(&root->fs_info->chunk_mutex);
                return ret;
        }
        buf->f_bavail += total_free_data;
        buf->f_bavail = buf->f_bavail >> bits;
        mutex_unlock(&root->fs_info->chunk_mutex);

        /* We treat it as constant endianness (it doesn't matter _which_)
           because we want the fsid to come out the same whether mounted
           on a big-endian or little-endian host */
        buf->f_fsid.val[0] = be32_to_cpu(fsid[0]) ^ be32_to_cpu(fsid[2]);
        buf->f_fsid.val[1] = be32_to_cpu(fsid[1]) ^ be32_to_cpu(fsid[3]);
        /* Mask in the root object ID too, to disambiguate subvols */
        buf->f_fsid.val[0] ^= BTRFS_I(dentry->d_inode)->root->objectid >> 32;
        buf->f_fsid.val[1] ^= BTRFS_I(dentry->d_inode)->root->objectid;

        return 0;
}

static struct file_system_type btrfs_fs_type = {
        .owner          = THIS_MODULE,
        .name           = "btrfs",
        .mount          = btrfs_mount,
        .kill_sb        = kill_anon_super,
        .fs_flags       = FS_REQUIRES_DEV,
};

/*
 * used by btrfsctl to scan devices when no FS is mounted
 */
static long btrfs_control_ioctl(struct file *file, unsigned int cmd,
                                unsigned long arg)
{
        struct btrfs_ioctl_vol_args *vol;
        struct btrfs_fs_devices *fs_devices;
        int ret = -ENOTTY;

        if (!capable(CAP_SYS_ADMIN))
                return -EPERM;

        vol = memdup_user((void __user *)arg, sizeof(*vol));
        if (IS_ERR(vol))
                return PTR_ERR(vol);

        switch (cmd) {
        case BTRFS_IOC_SCAN_DEV:
                ret = btrfs_scan_one_device(vol->name, FMODE_READ,
                                            &btrfs_fs_type, &fs_devices);
                break;
        }

        kfree(vol);
        return ret;
}

static int btrfs_freeze(struct super_block *sb)
{
        struct btrfs_root *root = btrfs_sb(sb);
        mutex_lock(&root->fs_info->transaction_kthread_mutex);
        mutex_lock(&root->fs_info->cleaner_mutex);
        return 0;
}

static int btrfs_unfreeze(struct super_block *sb)
{
        struct btrfs_root *root = btrfs_sb(sb);
        mutex_unlock(&root->fs_info->cleaner_mutex);
        mutex_unlock(&root->fs_info->transaction_kthread_mutex);
        return 0;
}

static const struct super_operations btrfs_super_ops = {
        .drop_inode     = btrfs_drop_inode,
        .evict_inode    = btrfs_evict_inode,
        .put_super      = btrfs_put_super,
        .sync_fs        = btrfs_sync_fs,
        .show_options   = btrfs_show_options,
        .write_inode    = btrfs_write_inode,
        .dirty_inode    = btrfs_dirty_inode,
        .alloc_inode    = btrfs_alloc_inode,
        .destroy_inode  = btrfs_destroy_inode,
        .statfs         = btrfs_statfs,
        .remount_fs     = btrfs_remount,
        .freeze_fs      = btrfs_freeze,
        .unfreeze_fs    = btrfs_unfreeze,
};

static const struct file_operations btrfs_ctl_fops = {
        .unlocked_ioctl  = btrfs_control_ioctl,
        .compat_ioctl = btrfs_control_ioctl,
        .owner   = THIS_MODULE,
        .llseek = noop_llseek,
};

static struct miscdevice btrfs_misc = {
        .minor          = BTRFS_MINOR,
        .name           = "btrfs-control",
        .fops           = &btrfs_ctl_fops
};

MODULE_ALIAS_MISCDEV(BTRFS_MINOR);
MODULE_ALIAS("devname:btrfs-control");

static int btrfs_interface_init(void)
{
        return misc_register(&btrfs_misc);
}

static void btrfs_interface_exit(void)
{
        if (misc_deregister(&btrfs_misc) < 0)
                printk(KERN_INFO "misc_deregister failed for control device");
}

static int __init init_btrfs_fs(void)
{
        int err;

        err = btrfs_init_sysfs();
        if (err)
                return err;

        err = btrfs_init_compress();
        if (err)
                goto free_sysfs;

        err = btrfs_init_cachep();
        if (err)
                goto free_compress;

        err = extent_io_init();
        if (err)
                goto free_cachep;

        err = extent_map_init();
        if (err)
                goto free_extent_io;

        err = btrfs_delayed_inode_init();
        if (err)
                goto free_extent_map;

        err = btrfs_interface_init();
        if (err)
                goto free_delayed_inode;

        err = register_filesystem(&btrfs_fs_type);
        if (err)
                goto unregister_ioctl;

        printk(KERN_INFO "%s loaded\n", BTRFS_BUILD_VERSION);
        return 0;

unregister_ioctl:
        btrfs_interface_exit();
free_delayed_inode:
        btrfs_delayed_inode_exit();
free_extent_map:
        extent_map_exit();
free_extent_io:
        extent_io_exit();
free_cachep:
        btrfs_destroy_cachep();
free_compress:
        btrfs_exit_compress();
free_sysfs:
        btrfs_exit_sysfs();
        return err;
}

static void __exit exit_btrfs_fs(void)
{
        btrfs_destroy_cachep();
        btrfs_delayed_inode_exit();
        extent_map_exit();
        extent_io_exit();
        btrfs_interface_exit();
        unregister_filesystem(&btrfs_fs_type);
        btrfs_exit_sysfs();
        btrfs_cleanup_fs_uuids();
        btrfs_exit_compress();
}

module_init(init_btrfs_fs)
module_exit(exit_btrfs_fs)

MODULE_LICENSE("GPL");