> On Oct 17, 2023, at 5:57 PM, Dragan Simic <dsimic@xxxxxxxxxxx> wrote:
>
> On 2023-10-18 01:06, junxiao.bi@xxxxxxxxxx wrote:
>> Anybody can help take a look at this patch?
>
> As a note, AFAIK it usually takes 7 to 10 days for the submitted patches to be reviewed.
Ah, I see. Thank you.
>
>
>>> On 10/12/23 2:55 PM, Junxiao Bi wrote:
>>> If a /dev/loopX is lost because someone might have removed it by mistake,
>>> future losetup operations on that loop device will fail.
>>> For examples, following cmds will fail when loop device file is lost.
>>> - "losetup -d $loop_device"
>>> - "losetup -f $file" or "mount $file $dev"
>>> Users can resurrect the loop device by recreating the device using mknod,
>>> but regular users might not be aware. Since /sysfs still have the loop
>>> device intact, this commit will detect that case by scanning sysfs and
>>> recreate the lost device file.
>>> Signed-off-by: Junxiao Bi <junxiao.bi@xxxxxxxxxx>
>>> ---
>>> lib/loopdev.c | 100 ++++++++++++++++++++++++++++++++++++++++----
>>> sys-utils/losetup.c | 14 +++----
>>> 2 files changed, 97 insertions(+), 17 deletions(-)
>>> diff --git a/lib/loopdev.c b/lib/loopdev.c
>>> index dae499f256fa..4fc617830bae 100644
>>> --- a/lib/loopdev.c
>>> +++ b/lib/loopdev.c
>>> @@ -279,6 +279,87 @@ static struct path_cxt *loopcxt_get_sysfs(struct loopdev_cxt *lc)
>>> return lc->sysfs;
>>> }
>>> +static int loopcxt_get_devid(struct loopdev_cxt *lc)
>>> +{
>>> + int devid = -1;
>>> + const char *p, *dev = loopcxt_get_device(lc);
>>> +
>>> + if (!dev)
>>> + return -EINVAL;
>>> +
>>> + p = strrchr(dev, '/');
>>> + if (!p || (sscanf(p, "/loop%d", &devid) != 1
>>> + && sscanf(p, "/%d", &devid) != 1))
>>> + return -EINVAL;
>>> +
>>> + return devid;
>>> +}
>>> +
>>> +/* scan sysfs entry for loop device. */
>>> +static int loopcxt_scan_sysfs(struct loopdev_cxt *lc)
>>> +{
>>> + struct dirent *d;
>>> + DIR *sysblock;
>>> + int nr;
>>> + char name[256];
>>> +
>>> + if (!loopcxt_sysfs_available(lc))
>>> + return 0;
>>> +
>>> + sysblock = opendir(_PATH_SYS_BLOCK);
>>> + if (!sysblock)
>>> + return 0;
>>> +
>>> + nr = loopcxt_get_devid(lc);
>>> + sprintf(name, "loop%d", nr);
>>> +
>>> + while ((d = readdir(sysblock))) {
>>> + if (!strcmp(d->d_name, name))
>>> + return 1;
>>> + }
>>> +
>>> + return 0;
>>> +}
>>> +
>>> +/*
>>> + * losetup cmds could fail if /dev/loopX is removed by mistake.
>>> + * This function will try to detect whether that is case,
>>> + * if so, it will recreate the device file and open it.
>>> + * Return fd if succeed, otherwise negative error code.
>>> + */
>>> +static int loopcxt_fix_lost_device_file(struct loopdev_cxt *lc)
>>> +{
>>> + char path[PATH_MAX];
>>> + int nr, ret;
>>> + FILE *fp;
>>> + unsigned int major, minor;
>>> +
>>> + if (!loopcxt_scan_sysfs(lc))
>>> + return -1;
>>> +
>>> + nr = loopcxt_get_devid(lc);
>>> + if (nr < 0)
>>> + return -1;
>>> + ret = snprintf(path, PATH_MAX, "%s/loop%d/dev",
>>> + _PATH_SYS_BLOCK, nr);
>>> + if (ret <= 0 || ret >= PATH_MAX)
>>> + return -1;
>>> + fp = fopen(path, "r");
>>> + if (!fp)
>>> + return -1;
>>> + ret = fscanf(fp, "%d:%d", &major, &minor);
>>> + fclose(fp);
>>> + if (ret != 2)
>>> + return -1;
>>> + sprintf(path, "/dev/loop%d", nr);
>>> + /* default loop device permission is "brw-rw----" */
>>> + umask(0003);
>>> + ret = mknod(path, S_IFBLK|0660, makedev(major, minor));
>>> + if (ret)
>>> + return -1;
>>> + return open(path, lc->mode | O_CLOEXEC);
>>> +}
>>> +
>>> static int __loopcxt_get_fd(struct loopdev_cxt *lc, mode_t mode)
>>> {
>>> int old = -1;
>>> @@ -303,7 +384,17 @@ static int __loopcxt_get_fd(struct loopdev_cxt *lc, mode_t mode)
>>> DBG(CXT, ul_debugobj(lc, "open %s [%s]: %m", lc->device,
>>> mode == O_RDONLY ? "ro" :
>>> mode == O_RDWR ? "rw" : "??"));
>>> -
>>> + /* loop device file not exist. */
>>> + if (lc->fd < 0 && errno == ENOENT) {
>>> + lc->fd = loopcxt_fix_lost_device_file(lc);
>>> + DBG(CXT, ul_debugobj(lc, "recreate %s fd %d",
>>> + lc->device, lc->fd));
>>> + /* loop file is not lost but doesn't exist,
>>> + * reset errno to have user know.
>>> + */
>>> + if (lc->fd < 0)
>>> + errno = ENOENT;
>>> + }
>>> if (lc->fd < 0 && old >= 0) {
>>> /* restore original on error */
>>> lc->fd = old;
>>> @@ -416,13 +507,6 @@ static int loopiter_set_device(struct loopdev_cxt *lc, const char *device)
>>> !(lc->iter.flags & LOOPITER_FL_FREE))
>>> return 0; /* caller does not care about device status */
>>> - if (!is_loopdev(lc->device)) {
>>> - DBG(ITER, ul_debugobj(&lc->iter, "%s does not exist", lc->device));
>>> - return -errno;
>>> - }
>>> -
>>> - DBG(ITER, ul_debugobj(&lc->iter, "%s exist", lc->device));
>>> -
>>> used = loopcxt_get_offset(lc, NULL) == 0;
>>> if ((lc->iter.flags & LOOPITER_FL_USED) && used)
>>> diff --git a/sys-utils/losetup.c b/sys-utils/losetup.c
>>> index 0ca910ae3347..b45cc2ee8f3c 100644
>>> --- a/sys-utils/losetup.c
>>> +++ b/sys-utils/losetup.c
>>> @@ -653,7 +653,7 @@ static int create_loop(struct loopdev_cxt *lc,
>>> }
>>> /* errors */
>>> - errpre = hasdev && loopcxt_get_fd(lc) < 0 ?
>>> + errpre = hasdev && lc->fd < 0 ?
>>> loopcxt_get_device(lc) : file;
>>> warn(_("%s: failed to set up loop device"), errpre);
>>> break;
>>> @@ -741,8 +741,7 @@ int main(int argc, char **argv)
>>> break;
>>> case 'c':
>>> act = A_SET_CAPACITY;
>>> - if (!is_loopdev(optarg) ||
>>> - loopcxt_set_device(&lc, optarg))
>>> + if (loopcxt_set_device(&lc, optarg))
>>> err(EXIT_FAILURE, _("%s: failed to use device"),
>>> optarg);
>>> break;
>>> @@ -754,8 +753,7 @@ int main(int argc, char **argv)
>>> break;
>>> case 'd':
>>> act = A_DELETE;
>>> - if (!is_loopdev(optarg) ||
>>> - loopcxt_set_device(&lc, optarg))
>>> + if (loopcxt_set_device(&lc, optarg))
>>> err(EXIT_FAILURE, _("%s: failed to use device"),
>>> optarg);
>>> break;
>>> @@ -883,8 +881,7 @@ int main(int argc, char **argv)
>>> else
>>> act = A_SHOW_ONE;
>>> - if (!is_loopdev(argv[optind]) ||
>>> - loopcxt_set_device(&lc, argv[optind]))
>>> + if (loopcxt_set_device(&lc, argv[optind]))
>>> err(EXIT_FAILURE, _("%s: failed to use device"),
>>> argv[optind]);
>>> optind++;
>>> @@ -935,8 +932,7 @@ int main(int argc, char **argv)
>>> case A_DELETE:
>>> res = delete_loop(&lc);
>>> while (optind < argc) {
>>> - if (!is_loopdev(argv[optind]) ||
>>> - loopcxt_set_device(&lc, argv[optind]))
>>> + if (loopcxt_set_device(&lc, argv[optind]))
>>> warn(_("%s: failed to use device"),
>>> argv[optind]);
>>> optind++;
