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Allow auto-destruction of loop devices

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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

[akpm@linux-foundation.org: coding-style fixes]
Signed-off-by: David Woodhouse <dwmw2@infradead.org>
Cc: Bernardo Innocenti <bernie@codewiz.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
This commit is contained in:
David Woodhouse 2008-02-06 01:36:27 -08:00 committed by Linus Torvalds
parent a3b81113fb
commit 96c5865559
2 changed files with 9 additions and 0 deletions
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8
drivers/block/loop.c
View file

@ -973,6 +973,10 @@ loop_set_status(struct loop_device *lo, const struct loop_info64 *info)
lo->transfer = xfer->transfer; lo->transfer = xfer->transfer;
lo->ioctl = xfer->ioctl; 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_encrypt_key_size = info->lo_encrypt_key_size;
lo->lo_init[0] = info->lo_init[0]; lo->lo_init[0] = info->lo_init[0];
lo->lo_init[1] = info->lo_init[1]; lo->lo_init[1] = info->lo_init[1];
@ -1331,6 +1335,10 @@ static int lo_release(struct inode *inode, struct file *file)
mutex_lock(&lo->lo_ctl_mutex); mutex_lock(&lo->lo_ctl_mutex);
--lo->lo_refcnt; --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); mutex_unlock(&lo->lo_ctl_mutex);
return 0; return 0;

1
include/linux/loop.h
View file

@ -76,6 +76,7 @@ struct loop_device {
enum { enum {
LO_FLAGS_READ_ONLY = 1, LO_FLAGS_READ_ONLY = 1,
LO_FLAGS_USE_AOPS = 2, LO_FLAGS_USE_AOPS = 2,
LO_FLAGS_AUTOCLEAR = 4,
}; };
#include <asm/posix_types.h> /* for __kernel_old_dev_t */ #include <asm/posix_types.h> /* for __kernel_old_dev_t */