From: Anand Jain anand.jain@oracle.com
commit 4faf55b03823e96c44dc4e364520000ed3b12fdb upstream.
->show_devname currently shows the lowest devid in the list. As the seed devices have the lowest devid in the sprouted filesystem, the userland tool such as findmnt end up seeing seed device instead of the device from the read-writable sprouted filesystem. As shown below.
mount /dev/sda /btrfs mount: /btrfs: WARNING: device write-protected, mounted read-only.
findmnt --output SOURCE,TARGET,UUID /btrfs SOURCE TARGET UUID /dev/sda /btrfs 899f7027-3e46-4626-93e7-7d4c9ad19111
btrfs dev add -f /dev/sdb /btrfs
umount /btrfs mount /dev/sdb /btrfs
findmnt --output SOURCE,TARGET,UUID /btrfs SOURCE TARGET UUID /dev/sda /btrfs 899f7027-3e46-4626-93e7-7d4c9ad19111
All sprouts from a single seed will show the same seed device and the same fsid. That's confusing. This is causing problems in our prototype as there isn't any reference to the sprout file-system(s) which is being used for actual read and write.
This was added in the patch which implemented the show_devname in btrfs commit 9c5085c14798 ("Btrfs: implement ->show_devname"). I tried to look for any particular reason that we need to show the seed device, there isn't any.
So instead, do not traverse through the seed devices, just show the lowest devid in the sprouted fsid.
After the patch:
mount /dev/sda /btrfs mount: /btrfs: WARNING: device write-protected, mounted read-only.
findmnt --output SOURCE,TARGET,UUID /btrfs SOURCE TARGET UUID /dev/sda /btrfs 899f7027-3e46-4626-93e7-7d4c9ad19111
btrfs dev add -f /dev/sdb /btrfs mount -o rw,remount /dev/sdb /btrfs
findmnt --output SOURCE,TARGET,UUID /btrfs SOURCE TARGET UUID /dev/sdb /btrfs 595ca0e6-b82e-46b5-b9e2-c72a6928be48
mount /dev/sda /btrfs1 mount: /btrfs1: WARNING: device write-protected, mounted read-only.
btrfs dev add -f /dev/sdc /btrfs1
findmnt --output SOURCE,TARGET,UUID /btrfs1 SOURCE TARGET UUID /dev/sdc /btrfs1 ca1dbb7a-8446-4f95-853c-a20f3f82bdbb
cat /proc/self/mounts | grep btrfs /dev/sdb /btrfs btrfs rw,relatime,noacl,space_cache,subvolid=5,subvol=/ 0 0 /dev/sdc /btrfs1 btrfs ro,relatime,noacl,space_cache,subvolid=5,subvol=/ 0 0
Reported-by: Martin K. Petersen martin.petersen@oracle.com CC: stable@vger.kernel.org # 4.19+ Tested-by: Martin K. Petersen martin.petersen@oracle.com Signed-off-by: Anand Jain anand.jain@oracle.com Reviewed-by: David Sterba dsterba@suse.com Signed-off-by: David Sterba dsterba@suse.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org
--- fs/btrfs/super.c | 21 +++++++-------------- 1 file changed, 7 insertions(+), 14 deletions(-)
--- a/fs/btrfs/super.c +++ b/fs/btrfs/super.c @@ -2254,9 +2254,7 @@ static int btrfs_unfreeze(struct super_b static int btrfs_show_devname(struct seq_file *m, struct dentry *root) { struct btrfs_fs_info *fs_info = btrfs_sb(root->d_sb); - struct btrfs_fs_devices *cur_devices; struct btrfs_device *dev, *first_dev = NULL; - struct list_head *head;
/* * Lightweight locking of the devices. We should not need @@ -2266,18 +2264,13 @@ static int btrfs_show_devname(struct seq * least until the rcu_read_unlock. */ rcu_read_lock(); - cur_devices = fs_info->fs_devices; - while (cur_devices) { - head = &cur_devices->devices; - list_for_each_entry_rcu(dev, head, dev_list) { - if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state)) - continue; - if (!dev->name) - continue; - if (!first_dev || dev->devid < first_dev->devid) - first_dev = dev; - } - cur_devices = cur_devices->seed; + list_for_each_entry_rcu(dev, &fs_info->fs_devices->devices, dev_list) { + if (test_bit(BTRFS_DEV_STATE_MISSING, &dev->dev_state)) + continue; + if (!dev->name) + continue; + if (!first_dev || dev->devid < first_dev->devid) + first_dev = dev; }
if (first_dev)