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btrfs: allow mounting btrfs subvolumes with different ro/rw options 

Given the following /etc/fstab entries:

/dev/sda3 /mnt/foo btrfs subvol=foo,ro 0 0
/dev/sda3 /mnt/bar btrfs subvol=bar,rw 0 0

you can't issue:

$ mount /mnt/foo
$ mount /mnt/bar

You would have to do:

$ mount /mnt/foo
$ mount -o remount,rw /mnt/foo
$ mount --bind -o remount,ro /mnt/foo
$ mount /mnt/bar

or

$ mount /mnt/bar
$ mount --rw /mnt/foo
$ mount --bind -o remount,ro /mnt/foo

With this patch you can do

$ mount /mnt/foo
$ mount /mnt/bar

$ cat /proc/self/mountinfo
49 33 0:41 /foo /mnt/foo ro,relatime shared:36 - btrfs /dev/sda3 rw,ssd,space_cache
87 33 0:41 /bar /mnt/bar rw,relatime shared:74 - btrfs /dev/sda3 rw,ssd,space_cache

Signed-off-by: Chris Mason <clm@fb.com>
This commit is contained in:
Harald Hoyer 2013-11-19 11:36:05 +01:00 committed by Chris Mason
parent 36523e9512
commit 0723a0473f
1 changed files with 22 additions and 0 deletions
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22
fs/btrfs/super.c
View File

@ -66,6 +66,8 @@
static const struct super_operations btrfs_super_ops;
static struct file_system_type btrfs_fs_type;
static int btrfs_remount(struct super_block *sb, int *flags, char *data);
static const char *btrfs_decode_error(int errno)
{
char *errstr = "unknown";
@ -1185,6 +1187,26 @@ static struct dentry *mount_subvol(const char *subvol_name, int flags,
mnt = vfs_kern_mount(&btrfs_fs_type, flags, device_name,
newargs);
kfree(newargs);
if (PTR_RET(mnt) == -EBUSY) {
if (flags & MS_RDONLY) {
mnt = vfs_kern_mount(&btrfs_fs_type, flags & ~MS_RDONLY, device_name,
newargs);
} else {
int r;
mnt = vfs_kern_mount(&btrfs_fs_type, flags | MS_RDONLY, device_name,
newargs);
if (IS_ERR(mnt))
return ERR_CAST(mnt);
r = btrfs_remount(mnt->mnt_sb, &flags, NULL);
if (r < 0) {
/* FIXME: release vfsmount mnt ??*/
return ERR_PTR(r);
}
}
}
if (IS_ERR(mnt))
return ERR_CAST(mnt);