From: David Woodhouse This allows a flag to be set on loop devices so that when they are closed for the last time, they'll self-destruct. In general, so that we can automatically allocate loop devices (as with losetup -f) and have them disappear when we're done with them. In particular, right now, so that we can stop relying on the hackish special-case in umount(8) which kills off loop devices which were set up by 'mount -oloop'. That means we can stop putting crap in /etc/mtab which doesn't belong there, which means it can be a symlink to /proc/mounts, which means yet another writable file on the root filesystem is eliminated and the 'stateless' folks get happier... and OLPC trac #356 can be closed. The mount(8) side of that is at http://marc.info/?l=util-linux-ng&m=119362955431694&w=2 Signed-off-by: David Woodhouse Cc: Bernardo Innocenti Signed-off-by: Andrew Morton --- drivers/block/loop.c | 8 ++++++++ include/linux/loop.h | 1 + 2 files changed, 9 insertions(+) diff -puN drivers/block/loop.c~allow-auto-destruction-of-loop-devices drivers/block/loop.c --- a/drivers/block/loop.c~allow-auto-destruction-of-loop-devices +++ a/drivers/block/loop.c @@ -973,6 +973,10 @@ loop_set_status(struct loop_device *lo, lo->transfer = xfer->transfer; lo->ioctl = xfer->ioctl; + if ( (lo->lo_flags & LO_FLAGS_AUTOCLEAR) != + (info->lo_flags & LO_FLAGS_AUTOCLEAR)) + lo->lo_flags ^= LO_FLAGS_AUTOCLEAR; + lo->lo_encrypt_key_size = info->lo_encrypt_key_size; lo->lo_init[0] = info->lo_init[0]; lo->lo_init[1] = info->lo_init[1]; @@ -1331,6 +1335,10 @@ static int lo_release(struct inode *inod mutex_lock(&lo->lo_ctl_mutex); --lo->lo_refcnt; + + if ((lo->lo_flags & LO_FLAGS_AUTOCLEAR) && !lo->lo_refcnt) + loop_clr_fd(lo, inode->i_bdev); + mutex_unlock(&lo->lo_ctl_mutex); return 0; diff -puN include/linux/loop.h~allow-auto-destruction-of-loop-devices include/linux/loop.h --- a/include/linux/loop.h~allow-auto-destruction-of-loop-devices +++ a/include/linux/loop.h @@ -76,6 +76,7 @@ struct loop_device { enum { LO_FLAGS_READ_ONLY = 1, LO_FLAGS_USE_AOPS = 2, + LO_FLAGS_AUTOCLEAR = 4, }; #include /* for __kernel_old_dev_t */ _