[PATCH v2 6/7] loopfs: start attaching correct namespace during loop_add()

[Christian Brauner <christian.brauner@ubuntu.com>]

Tag loop devices with the namespace the loopfs instance was mounted in.
This has the consequence that loopfs devices carry the correct sysfs
permissions for all their core files. All other devices files will
continue to be correctly owned by the initial namespaces. Here is sample
output:

root@b1:~# mount -t loop loop /mnt
root@b1:~# ln -sf /mnt/loop-control /dev/loop-control
root@b1:~# losetup -f
/dev/loop8
root@b1:~# ln -sf /mnt/loop8 /dev/loop8
root@b1:~# ls -al /sys/class/block/loop8
lrwxrwxrwx 1 root root 0 Apr  7 13:06 /sys/class/block/loop8 -> ../../devices/virtual/block/loop8
root@b1:~# ls -al /sys/class/block/loop8/
total 0
drwxr-xr-x  9 root   root       0 Apr  7 13:06 .
drwxr-xr-x 18 nobody nogroup    0 Apr  7 13:07 ..
-r--r--r--  1 root   root    4096 Apr  7 13:06 alignment_offset
lrwxrwxrwx  1 nobody nogroup    0 Apr  7 13:07 bdi -> ../../bdi/7:8
-r--r--r--  1 root   root    4096 Apr  7 13:06 capability
-r--r--r--  1 root   root    4096 Apr  7 13:06 dev
-r--r--r--  1 root   root    4096 Apr  7 13:06 discard_alignment
-r--r--r--  1 root   root    4096 Apr  7 13:06 events
-r--r--r--  1 root   root    4096 Apr  7 13:06 events_async
-rw-r--r--  1 root   root    4096 Apr  7 13:06 events_poll_msecs
-r--r--r--  1 root   root    4096 Apr  7 13:06 ext_range
-r--r--r--  1 root   root    4096 Apr  7 13:06 hidden
drwxr-xr-x  2 nobody nogroup    0 Apr  7 13:07 holders
-r--r--r--  1 root   root    4096 Apr  7 13:06 inflight
drwxr-xr-x  2 nobody nogroup    0 Apr  7 13:07 integrity
drwxr-xr-x  3 nobody nogroup    0 Apr  7 13:07 mq
drwxr-xr-x  2 root   root       0 Apr  7 13:06 power
drwxr-xr-x  3 nobody nogroup    0 Apr  7 13:07 queue
-r--r--r--  1 root   root    4096 Apr  7 13:06 range
-r--r--r--  1 root   root    4096 Apr  7 13:06 removable
-r--r--r--  1 root   root    4096 Apr  7 13:06 ro
-r--r--r--  1 root   root    4096 Apr  7 13:06 size
drwxr-xr-x  2 nobody nogroup    0 Apr  7 13:07 slaves
-r--r--r--  1 root   root    4096 Apr  7 13:06 stat
lrwxrwxrwx  1 nobody nogroup    0 Apr  7 13:07 subsystem -> ../../../../class/block
drwxr-xr-x  2 root   root       0 Apr  7 13:06 trace
-rw-r--r--  1 root   root    4096 Apr  7 13:06 uevent
root@b1:~#

Cc: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
---
/* v2 */
unchanged
- Christian Brauner <christian.brauner@ubuntu.com>:
  - Adapted commit message otherwise unchanged.
---
 drivers/block/loop.c | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/drivers/block/loop.c b/drivers/block/loop.c
index 8e21d4b33e01..2dc53bad4b48 100644
--- a/drivers/block/loop.c
+++ b/drivers/block/loop.c
@@ -2212,6 +2212,10 @@ static int loop_add(struct loop_device **l, int i, struct inode *inode)
 	disk->private_data	= lo;
 	disk->queue		= lo->lo_queue;
 	sprintf(disk->disk_name, "loop%d", i);
+#ifdef CONFIG_BLK_DEV_LOOPFS
+	if (loopfs_i_sb(inode))
+		disk->user_ns = loopfs_i_sb(inode)->s_user_ns;
+#endif
 
 	add_disk(disk);
 
-- 
2.26.1