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authorDenys Vlasenko2017-03-16 16:49:37 +0100
committerDenys Vlasenko2017-03-16 16:55:47 +0100
commitab518eea9c41235a3fcde80f3ea99669eaade621 (patch)
tree4bd1783e343316fa11c2ade135dbe0b0561689a9 /util-linux
parent018804204f41e6e60cec536843275f8fdd4d3620 (diff)
downloadbusybox-ab518eea9c41235a3fcde80f3ea99669eaade621.zip
busybox-ab518eea9c41235a3fcde80f3ea99669eaade621.tar.gz
mount: create loop devices with LO_FLAGS_AUTOCLEAR flag
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>
Diffstat (limited to 'util-linux')
-rw-r--r--util-linux/losetup.c27
-rw-r--r--util-linux/mount.c21
2 files changed, 46 insertions, 2 deletions
diff --git a/util-linux/losetup.c b/util-linux/losetup.c
index 4424d9c..d356f49 100644
--- a/util-linux/losetup.c
+++ b/util-linux/losetup.c
@@ -127,12 +127,37 @@ int losetup_main(int argc UNUSED_PARAM, char **argv)
d = *argv++;
if (argv[0]) {
- if (set_loop(&d, argv[0], offset, (opt & OPT_r)) < 0)
+ if (set_loop(&d, argv[0], offset, (opt & OPT_r) ? BB_LO_FLAGS_READ_ONLY : 0) < 0)
bb_simple_perror_msg_and_die(argv[0]);
return EXIT_SUCCESS;
}
}
+ /* TODO: util-linux 2.28 shows this when run w/o params:
+ * NAME SIZELIMIT OFFSET AUTOCLEAR RO BACK-FILE DIO
+ * /dev/loop0 0 0 1 0 /PATH/TO/FILE 0
+ *
+ * implemented by reading /sys:
+ *
+ * open("/sys/block", O_RDONLY|O_NONBLOCK|O_DIRECTORY|O_CLOEXEC) = 3
+ * newfstatat(3, "loop0/loop/backing_file", {st_mode=S_IFREG|0444, st_size=4096, ...}, 0) = 0
+ * stat("/dev/loop0", {st_mode=S_IFBLK|0660, st_rdev=makedev(7, 0), ...}) = 0
+ * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
+ * read(5, "0\n", 4096) = 2
+ * open("/sys/dev/block/7:0/loop/sizelimit", O_RDONLY|O_CLOEXEC) = 5
+ * read(5, "0\n", 4096) = 2
+ * open("/sys/dev/block/7:0/loop/offset", O_RDONLY|O_CLOEXEC) = 5
+ * read(5, "0\n", 4096) = 2
+ * open("/sys/dev/block/7:0/loop/autoclear", O_RDONLY|O_CLOEXEC) = 5
+ * read(5, "1\n", 4096) = 2
+ * open("/sys/dev/block/7:0/ro", O_RDONLY|O_CLOEXEC) = 5
+ * read(5, "0\n", 4096) = 2
+ * open("/sys/dev/block/7:0/loop/backing_file", O_RDONLY|O_CLOEXEC) = 5
+ * read(5, "/PATH/TO/FILE", 4096) = 37
+ * open("/sys/dev/block/7:0/loop/dio", O_RDONLY|O_CLOEXEC) = 5
+ * read(5, "0\n", 4096) = 2
+ */
+
bb_show_usage(); /* does not return */
/*return EXIT_FAILURE;*/
}
diff --git a/util-linux/mount.c b/util-linux/mount.c
index f0245f7..6bb1852 100644
--- a/util-linux/mount.c
+++ b/util-linux/mount.c
@@ -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))