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loop-util: LOOP_CONFIGURE ignores lo_sizelimit 

It appears LOOP_CONFIGURE in 5.8 is even more broken than initially
thought: it doesn't properly propgate lo_sizelimit to the block device
layer. :-(

Let's hence check the block device size immediately after issuing
LOOP_CONFIGURE, and if it doesn't match what we just set let's fallback
to the old ioctls.

This means LOOP_CONFIGURE currently works correctly only for the most
simply case: no partition table logic and no size limit. Sad!

(Kernel people should really be told about the concepts of tests and
even CI, one day!)
This commit is contained in:
Lennart Poettering 2020-08-24 18:11:06 +02:00
parent c2f418d595
commit bb2551bdcb
1 changed files with 34 additions and 10 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

44
src/shared/loop-util.c
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@ -47,18 +47,42 @@ static int loop_configure(int fd, const struct loop_config *c) {
if (!ERRNO_IS_NOT_SUPPORTED(errno) && errno != EINVAL)
return -errno;
} else {
if (!FLAGS_SET(c->info.lo_flags, LO_FLAGS_PARTSCAN))
bool good = true;
if (c->info.lo_sizelimit != 0) {
/* Kernel 5.8 vanilla doesn't properly propagate the size limit into the block
* device. If it's used, let's immediately check if it had the desired effect
* hence. And if not use classic LOOP_SET_STATUS64. */
uint64_t z;
if (ioctl(fd, BLKGETSIZE64, &z) < 0) {
r = -errno;
goto fail;
}
if (z != c->info.lo_sizelimit) {
log_debug("LOOP_CONFIGURE is broken, doesn't honour .lo_sizelimit. Falling back to LOOP_SET_STATUS64.");
good = false;
}
}
if (FLAGS_SET(c->info.lo_flags, LO_FLAGS_PARTSCAN)) {
/* Kernel 5.8 vanilla doesn't properly propagate the partition scanning flag into the
* block device. Let's hence verify if things work correctly here before
* returning. */
r = blockdev_partscan_enabled(fd);
if (r < 0)
goto fail;
if (r == 0) {
log_debug("LOOP_CONFIGURE is broken, doesn't honour LO_FLAGS_PARTSCAN. Falling back to LOOP_SET_STATUS64.");
good = false;
}
}
if (good)
return 0;
/* Kernel 5.8 vanilla doesn't properly propagate the partition scanning flag into the
* block device. Let's hence verify if things work correctly here before returning. */
r = blockdev_partscan_enabled(fd);
if (r < 0)
goto fail;
if (r > 0)
return 0; /* All is good. */
/* Otherwise, undo the attachment and use the old APIs */
(void) ioctl(fd, LOOP_CLR_FD);
}