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lklfuse: add lock parameter to avoid duplicate mounts

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This lock-while-mounted behaviour is similar to what QEMU does, and can
help avoid duplicate mounts.
Allowing for an explicit lock path that differs from the filesystem
image / block device path was intentional, to ensure non-flock
supporting filesystems can still be used. Also, there are cases where
a block device and partition (e.g. sda and sda1) can both provide access
to the same filesystem image, in which case an FS-ID based lock would
make sense.

Signed-off-by: David Disseldorp <ddiss@suse.de>
This commit is contained in:
David Disseldorp
2025-07-02 10:10:40 +02:00
parent 46f599b057
commit 29e4402a82
2 changed files with 27 additions and 4 deletions
Download Patch File Download Diff File Expand all files Collapse all files

4
Documentation/lkl/lklfuse.rst
View File

@@ -39,7 +39,9 @@ OPTIONS
-o part=parition mount <partition>.
-o ro open file read-only.
-o ro open block-device read-only.
-o lock=<file> only mount after taking an exclusive lock on <file>.
-o opts=options Linux kernel mount <options> (use \\ to escape , and =).

27
tools/lkl/lklfuse.c
View File

@@ -6,6 +6,7 @@
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
#include <sys/file.h>
#include <sys/stat.h>
#include <string.h>
#include <errno.h>
@@ -24,6 +25,7 @@ struct lklfuse {
const char *log;
const char *type;
const char *opts;
const char *lock;
struct lkl_disk disk;
int disk_id;
int part;
@@ -46,6 +48,7 @@ static struct fuse_opt lklfuse_opts[] = {
LKLFUSE_OPT("mb=%d", mb, 0),
LKLFUSE_OPT("opts=%s", opts, 0),
LKLFUSE_OPT("part=%d", part, 0),
LKLFUSE_OPT("lock=%s", lock, 0),
FUSE_OPT_KEY("-h", KEY_HELP),
FUSE_OPT_KEY("--help", KEY_HELP),
FUSE_OPT_KEY("-V", KEY_VERSION),
@@ -58,7 +61,7 @@ static struct fuse_opt lklfuse_opts[] = {
static void usage(void)
{
printf(
"usage: lklfuse file mountpoint [options]\n"
"usage: lklfuse block-device mountpoint [options]\n"
"\n"
"general options:\n"
" -o opt,[opt...] mount options\n"
@@ -70,7 +73,8 @@ static void usage(void)
" -o type=fstype filesystem type\n"
" -o mb=memory amount of memory to allocate in MB (default: 64)\n"
" -o part=parition partition to mount\n"
" -o ro open file read-only\n"
" -o ro open block-device read-only\n"
" -o lock=FILE only mount after taking an exclusive lock on FILE\n"
" -o opts=options mount options (use \\ to escape , and =)\n"
);
}
@@ -791,7 +795,7 @@ int main(int argc, char **argv)
struct fuse_cmdline_opts cli_opts;
struct fuse *fuse;
struct stat st;
int ret;
int ret, lockfd = -1;
if (fuse_opt_parse(&args, &lklfuse, lklfuse_opts, lklfuse_opt_proc))
return 1;
@@ -801,6 +805,23 @@ int main(int argc, char **argv)
return 1;
}
if (lklfuse.lock) {
lockfd = open(lklfuse.lock, O_RDWR | O_CREAT, 0644);
if (lockfd < 0) {
fprintf(stderr, "failed to open %s: %s\n",
lklfuse.lock, strerror(errno));
return 1;
}
ret = flock(lockfd, LOCK_EX | LOCK_NB);
if (ret < 0) {
fprintf(stderr, "unable to exclusively lock %s: %s\n",
lklfuse.lock, strerror(errno));
return 2;
}
/* lock dropped when lockfd is closed on program exit */
}
if (fuse_parse_cmdline(&args, &cli_opts))
return 1;