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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

49
libbb/loop.c
View File

@@ -78,22 +78,24 @@ int FAST_FUNC del_loop(const char *device)
return rc;
}
/* Returns 0 if mounted RW, 1 if mounted read-only, <0 for error.
*device is loop device to use, or if *device==NULL finds a loop device to
mount it on and sets *device to a strdup of that loop device name. This
search will re-use an existing loop device already bound to that
file/offset if it finds one.
/* Returns opened fd to the loop device, <0 on error.
* *device is loop device to use, or if *device==NULL finds a loop device to
* mount it on and sets *device to a strdup of that loop device name. This
* search will re-use an existing loop device already bound to that
* file/offset if it finds one.
*/
int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset, int ro)
int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offset, unsigned flags)
{
char dev[LOOP_NAMESIZE];
char *try;
bb_loop_info loopinfo;
struct stat statbuf;
int i, dfd, ffd, mode, rc = -1;
int i, dfd, ffd, mode, rc;
rc = dfd = -1;
/* Open the file. Barf if this doesn't work. */
mode = ro ? O_RDONLY : O_RDWR;
mode = (flags & BB_LO_FLAGS_READ_ONLY) ? O_RDONLY : O_RDWR;
open_ffd:
ffd = open(file, mode);
if (ffd < 0) {
@@ -144,20 +146,35 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
/* If device is free, claim it. */
if (rc && errno == ENXIO) {
memset(&loopinfo, 0, sizeof(loopinfo));
safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);
loopinfo.lo_offset = offset;
/* Associate free loop device with file. */
if (ioctl(dfd, LOOP_SET_FD, ffd) == 0) {
if (ioctl(dfd, BB_LOOP_SET_STATUS, &loopinfo) == 0)
rc = 0;
else
memset(&loopinfo, 0, sizeof(loopinfo));
safe_strncpy((char *)loopinfo.lo_file_name, file, LO_NAME_SIZE);
loopinfo.lo_offset = offset;
/*
* Used by mount to set LO_FLAGS_AUTOCLEAR.
* LO_FLAGS_READ_ONLY is not set because RO is controlled by open type of the file.
* Note that closing LO_FLAGS_AUTOCLEARed dfd before mount
* is wrong (would free the loop device!)
*/
loopinfo.lo_flags = (flags & ~BB_LO_FLAGS_READ_ONLY);
rc = ioctl(dfd, BB_LOOP_SET_STATUS, &loopinfo);
if (rc != 0 && (loopinfo.lo_flags & BB_LO_FLAGS_AUTOCLEAR)) {
/* Old kernel, does not support LO_FLAGS_AUTOCLEAR? */
/* (this code path is not tested) */
loopinfo.lo_flags -= BB_LO_FLAGS_AUTOCLEAR;
rc = ioctl(dfd, BB_LOOP_SET_STATUS, &loopinfo);
}
if (rc != 0) {
ioctl(dfd, LOOP_CLR_FD, 0);
}
}
} else {
rc = -1;
}
close(dfd);
if (rc != 0) {
close(dfd);
}
try_again:
if (*device) break;
}
@@ -165,7 +182,7 @@ int FAST_FUNC set_loop(char **device, const char *file, unsigned long long offse
if (rc == 0) {
if (!*device)
*device = xstrdup(dev);
return (mode == O_RDONLY); /* 1:ro, 0:rw */
return dfd;
}
return rc;
}