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mount: create loop devices with LO_FLAGS_AUTOCLEAR flag

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The "autolooped" mount (mount [-oloop] IMAGE /DIR/DIR)
always creates AUTOCLEARed loopdevs, so that umounting
drops them (and this does not require any code in the
umount userspace).
This happens since circa linux-2.6.25:
	commit 96c5865559cee0f9cbc5173f3c949f6ce3525581
	Date:    Wed Feb 6 01:36:27 2008 -0800
	Subject: Allow auto-destruction of loop devices
IOW: in this case, umount does not have to use -d
to drop the loopdev.

The explicit loop mount (mount /dev/loopN /DIR/DIR)
does not do this. In this case, umount without -d
should not drop loopdev.
Unfortunately, bbox umount currently always implies -d,
this probably needs fixing.

function                                             old     new   delta
set_loop                                             537     597     +60
singlemount                                         1101    1138     +37
losetup_main                                         419     432     +13
------------------------------------------------------------------------------
(add/remove: 0/0 grow/shrink: 3/0 up/down: 110/0)             Total: 110 bytes

Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
This commit is contained in:
Denys Vlasenko
2017-03-16 16:49:37 +01:00
parent 018804204f
commit ab518eea9c
4 changed files with 87 additions and 21 deletions
Download Patch File Download Diff File Expand all files Collapse all files

21
util-linux/mount.c
View File

@ -1887,6 +1887,7 @@ static int nfsmount(struct mntent *mp, unsigned long vfsflags, char *filteropts)
// NB: mp->xxx fields may be trashed on exit
static int singlemount(struct mntent *mp, int ignore_busy)
{
int loopfd = -1;
int rc = -1;
unsigned long vfsflags;
char *loopFile = NULL, *filteropts = NULL;
@ -2026,7 +2027,20 @@ static int singlemount(struct mntent *mp, int ignore_busy)
if (ENABLE_FEATURE_MOUNT_LOOP && S_ISREG(st.st_mode)) {
loopFile = bb_simplify_path(mp->mnt_fsname);
mp->mnt_fsname = NULL; // will receive malloced loop dev name
if (set_loop(&mp->mnt_fsname, loopFile, 0, /*ro:*/ (vfsflags & MS_RDONLY)) < 0) {
// mount always creates AUTOCLEARed loopdevs, so that umounting
// drops them without any code in the userspace.
// This happens since circa linux-2.6.25:
// commit 96c5865559cee0f9cbc5173f3c949f6ce3525581
// Date: Wed Feb 6 01:36:27 2008 -0800
// Subject: Allow auto-destruction of loop devices
loopfd = set_loop(&mp->mnt_fsname,
loopFile,
0,
((vfsflags & MS_RDONLY) ? BB_LO_FLAGS_READ_ONLY : 0)
| BB_LO_FLAGS_AUTOCLEAR
);
if (loopfd < 0) {
if (errno == EPERM || errno == EACCES)
bb_error_msg(bb_msg_perm_denied_are_you_root);
else
@ -2074,6 +2088,8 @@ static int singlemount(struct mntent *mp, int ignore_busy)
}
// If mount failed, clean up loop file (if any).
// (Newer kernels which support LO_FLAGS_AUTOCLEAR should not need this,
// merely "close(loopfd)" should do it?)
if (ENABLE_FEATURE_MOUNT_LOOP && rc && loopFile) {
del_loop(mp->mnt_fsname);
if (ENABLE_FEATURE_CLEAN_UP) {
@ -2086,6 +2102,9 @@ static int singlemount(struct mntent *mp, int ignore_busy)
if (ENABLE_FEATURE_CLEAN_UP)
free(filteropts);
if (loopfd >= 0)
close(loopfd);
if (errno == EBUSY && ignore_busy)
return 0;
if (errno == ENOENT && (vfsflags & MOUNT_NOFAIL))