Re: [PATCH V3] Btrfs: fix subvolume mount by name problem when default mount subvolume is set

[Andreas Philipp <philipp.andreas@gmail.com>]

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Just a (probably) short question. This means, one now can mount any
subvolume which lies directly in another subvolume by name, as long as
one passes the correct subvolrootid=X mount option?

Thanks,
Andreas Philipp

On 06.04.2011 09:33, Zhong, Xin wrote:
> We create two subvolumes (meego_root and meego_home) in
> btrfs root directory. And set meego_root as default mount
> subvolume. After we remount btrfs, meego_root is mounted
> to top directory by default. Then when we try to mount
> meego_home (subvol=meego_home) to a subdirectory, it failed.
> The problem is when default mount subvolume is set to
> meego_root, we search meego_home in meego_root but can not find
> it. So the solution is to add a new mount option (subvolrootid)
> to specify subvol id of root and search subvol name in it. For
> our case, now we can use "-o subvolrootid=0,subvol=meego_home)
> to mount meego_home.
>
> Detail information can be found in meego bugzilla:
> https://bugs.meego.com/show_bug.cgi?id=15055
>
> Signed-off-by: Zhong, Xin <xin.zhong@intel.com>
> ---
> fs/btrfs/super.c | 42 +++++++++++++++++++++++++++++++++---------
> 1 files changed, 33 insertions(+), 9 deletions(-)
>
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index db0a827..b85fe78 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -156,7 +156,7 @@ enum {
> 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_err,
> + Opt_enospc_debug, Opt_subvolrootid, Opt_err,
> };
>
> static match_table_t tokens = {
> @@ -186,6 +186,7 @@ static match_table_t tokens = {
> {Opt_clear_cache, "clear_cache"},
> {Opt_user_subvol_rm_allowed, "user_subvol_rm_allowed"},
> {Opt_enospc_debug, "enospc_debug"},
> + {Opt_subvolrootid, "subvolrootid=%d"},
> {Opt_err, NULL},
> };
>
> @@ -229,6 +230,7 @@ int btrfs_parse_options(struct btrfs_root *root,
char *options)
> break;
> case Opt_subvol:
> case Opt_subvolid:
> + case Opt_subvolrootid:
> case Opt_device:
> /*
> * These are parsed by btrfs_parse_early_options
> @@ -385,7 +387,7 @@ out:
> */
> static int btrfs_parse_early_options(const char *options, fmode_t flags,
> void *holder, char **subvol_name, u64 *subvol_objectid,
> - struct btrfs_fs_devices **fs_devices)
> + u64 *subvol_rootid, struct btrfs_fs_devices **fs_devices)
> {
> substring_t args[MAX_OPT_ARGS];
> char *opts, *orig, *p;
> @@ -426,6 +428,18 @@ static int btrfs_parse_early_options(const char
*options, fmode_t flags,
> *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);
> @@ -715,6 +729,7 @@ static int btrfs_get_sb(struct file_system_type
*fs_type, int flags,
> fmode_t mode = FMODE_READ;
> char *subvol_name = NULL;
> u64 subvol_objectid = 0;
> + u64 subvol_rootid = 0;
> int error = 0;
>
> if (!(flags & MS_RDONLY))
> @@ -722,7 +737,7 @@ static int btrfs_get_sb(struct file_system_type
*fs_type, int flags,
>
> error = btrfs_parse_early_options(data, mode, fs_type,
> &subvol_name, &subvol_objectid,
> - &fs_devices);
> + &subvol_rootid, &fs_devices);
> if (error)
> return error;
>
> @@ -786,15 +801,17 @@ static int btrfs_get_sb(struct file_system_type
*fs_type, int flags,
> s->s_flags |= MS_ACTIVE;
> }
>
> - root = get_default_root(s, subvol_objectid);
> - if (IS_ERR(root)) {
> - error = PTR_ERR(root);
> - deactivate_locked_super(s);
> - goto error_free_subvol_name;
> - }
> /* if they gave us a subvolume name bind mount into that */
> if (strcmp(subvol_name, ".")) {
> struct dentry *new_root;
> +
> + root = get_default_root(s, subvol_rootid);
> + if (IS_ERR(root)) {
> + error = PTR_ERR(root);
> + deactivate_locked_super(s);
> + goto error_free_subvol_name;
> + }
> +
> mutex_lock(&root->d_inode->i_mutex);
> new_root = lookup_one_len(subvol_name, root,
> strlen(subvol_name));
> @@ -815,6 +832,13 @@ static int btrfs_get_sb(struct file_system_type
*fs_type, int flags,
> }
> dput(root);
> root = new_root;
> + } else {
> + root = get_default_root(s, subvol_objectid);
> + if (IS_ERR(root)) {
> + error = PTR_ERR(root);
> + deactivate_locked_super(s);
> + goto error_free_subvol_name;
> + }
> }
>
> mnt->mnt_sb = s;
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