28.04.2017 12:14, Anand Jain пишет:
> We allow recursive mounts with subvol options such as [1]
>
> [1]
> mount -o rw,compress=lzo /dev/sdc /btrfs1
> mount -o ro,subvol=sv2 /dev/sdc /btrfs2
>
> And except for the btrfs-specific subvol and subvolid options
> all-other options are just ignored in the subsequent mounts.
>
> In the below example [2] the effect compression is only zlib,
> even though there was no error for the option -o compress=lzo.
>
> [2]
> ----
> # mount -o compress=zlib /dev/sdc /btrfs1
> #echo $?
> 0
>
> # mount -o compress=lzo /dev/sdc /btrfs
> #echo $?
> 0
>
> #cat /proc/self/mounts
> ::
> /dev/sdc /btrfs1 btrfs rw,relatime,compress=zlib,space_cache,subvolid=5,subvol=/ 0 0
> /dev/sdc /btrfs btrfs rw,relatime,compress=zlib,space_cache,subvolid=5,subvol=/ 0 0
> ----
>
> Further, random string .. has no error as well.
> -----
> # mount -o compress=zlib /dev/sdc /btrfs1
> #echo $?
> 0
>
> # mount -o something /dev/sdc /btrfs
> #echo $?
> 0
> -----
>
> This patch fixes the above issue, by checking the if the passed
> options are only subvol or subvolid in the subsequent mount.
>
> Signed-off-by: Anand Jain <anand.jain@xxxxxxxxxx>
> ---
> fs/btrfs/super.c | 40 ++++++++++++++++++++++++++++++++++++++++
> 1 file changed, 40 insertions(+)
>
> diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
> index 9530a333d302..e0e542345c38 100644
> --- a/fs/btrfs/super.c
> +++ b/fs/btrfs/super.c
> @@ -389,6 +389,44 @@ static const match_table_t tokens = {
> {Opt_err, NULL},
> };
>
> +static int parse_recursive_mount_options(char *data)
> +{
> + substring_t args[MAX_OPT_ARGS];
> + char *options, *orig;
> + char *p;
> + int ret = 0;
> +
> + /*
> + * This is not a remount thread, but we allow recursive mounts
> + * with varying RO/RW flag to support subvol-mounts. So error-out
> + * if any other option being passed in here.
> + */
> +
> + options = kstrdup(data, 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_subvol:
> + case Opt_subvolid:
> + break;
> + default:
> + ret = -EBUSY;
> + }
> + }
> +
> + kfree(orig);
> + return ret;
> +}
> +
> /*
> * Regular mount options parser. Everything that is needed only when
> * reading in a new superblock is parsed here.
> @@ -1611,6 +1649,8 @@ static struct dentry *btrfs_mount(struct file_system_type *fs_type, int flags,
> free_fs_info(fs_info);
> if ((flags ^ s->s_flags) & MS_RDONLY)
> error = -EBUSY;
> + if (parse_recursive_mount_options(data))
> + error = -EBUSY;
But if subvol= was passed, it should not reach this place at all -
btrfs_mount() returns earlier in
if (subvol_name || subvol_objectid != BTRFS_FS_TREE_OBJECTID) {
/* mount_subvol() will free subvol_name. */
return mount_subvol(subvol_name, subvol_objectid, flags,
device_name, data);
}
So check for subvol here seems redundant.
> } else {
> snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
> btrfs_sb(s)->bdev_holder = fs_type;
>
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