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loop-util: add more debugging logs in loop_configure()

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This commit is contained in:
Yu Watanabe
2023-03-19 20:32:09 +09:00
parent c22dcc80d0
commit 432f1fa8c7
1 changed files with 26 additions and 19 deletions
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src/shared/loop-util.c
+26 -19
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@@ -270,19 +270,19 @@ static int loop_configure(
assert(ret);
if (asprintf(&node, "/dev/loop%i", nr) < 0)
return -ENOMEM;
return log_oom_debug();
r = sd_device_new_from_devname(&dev, node);
if (r < 0)
return r;
return log_debug_errno(r, "Failed to create sd_device object for \"%s\": %m", node);
r = sd_device_get_devnum(dev, &devno);
if (r < 0)
return r;
return log_device_debug_errno(dev, r, "Failed to get devnum: %m");
fd = sd_device_open(dev, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
if (fd < 0)
return fd;
return log_device_debug_errno(dev, fd, "Failed to open device: %m");
/* Let's lock the device before we do anything. We take the BSD lock on a second, separately opened
* fd for the device. udev after all watches for close() events (specifically IN_CLOSE_WRITE) on
@@ -293,15 +293,18 @@ static int loop_configure(
* automatically release the lock, after we are done. */
lock_fd = open_lock_fd(fd, LOCK_EX);
if (lock_fd < 0)
return lock_fd;
return log_device_debug_errno(dev, lock_fd, "Failed to acquire lock: %m");
log_device_debug(dev, "Acquired exclusive lock.");
/* Let's see if backing file is really unattached. Someone may already attach a backing file without
* taking BSD lock. */
r = loop_is_bound(fd);
if (r < 0)
return r;
return log_device_debug_errno(dev, r, "Failed to check if the loopback block device is bound: %m");
if (r > 0)
return -EBUSY;
return log_device_debug_errno(dev, SYNTHETIC_ERRNO(EBUSY),
"The loopback block device is already bound, ignoring.");
/* Let's see if the device is really detached, i.e. currently has no associated partition block
* devices. On various kernels (such as 5.8) it is possible to have a loopback block device that
@@ -310,11 +313,12 @@ static int loop_configure(
* again. */
r = block_device_remove_all_partitions(dev, fd);
if (r < 0)
return r;
return log_device_debug_errno(dev, r, "Failed to remove partitions on the loopback block device: %m");
if (r > 0)
/* Removed all partitions. Let's report this to the caller, to try again, and count this as
* an attempt. */
return -EUCLEAN;
return log_device_debug_errno(dev, SYNTHETIC_ERRNO(EUCLEAN),
"Removed partitions on the loopback block device.");
if (!loop_configure_broken) {
/* Acquire uevent seqnum immediately before attaching the loopback device. This allows
@@ -325,7 +329,7 @@ static int loop_configure(
* use. But doing this at least shortens the race window a bit. */
r = get_current_uevent_seqnum(&seqnum);
if (r < 0)
return r;
return log_device_debug_errno(dev, r, "Failed to get the current uevent seqnum: %m");
timestamp = now(CLOCK_MONOTONIC);
@@ -335,7 +339,7 @@ static int loop_configure(
* rather than ENOTTY on loopback block devices. They should fix that in the kernel,
* but in the meantime we accept both here. */
if (!ERRNO_IS_NOT_SUPPORTED(errno) && errno != EINVAL)
return -errno;
return log_device_debug_errno(dev, errno, "ioctl(LOOP_CONFIGURE) failed: %m");
loop_configure_broken = true;
} else {
@@ -343,7 +347,7 @@ static int loop_configure(
r = loop_configure_verify(loop_with_fd, c);
if (r < 0)
return r;
return log_device_debug_errno(dev, r, "Failed to verify if loopback block device is correctly configured: %m");
if (r == 0) {
/* LOOP_CONFIGURE doesn't work. Remember that. */
loop_configure_broken = true;
@@ -363,12 +367,12 @@ static int loop_configure(
/* Let's read the seqnum again, to shorten the window. */
r = get_current_uevent_seqnum(&seqnum);
if (r < 0)
return r;
return log_device_debug_errno(dev, r, "Failed to get the current uevent seqnum: %m");
timestamp = now(CLOCK_MONOTONIC);
if (ioctl(fd, LOOP_SET_FD, c->fd) < 0)
return -errno;
return log_device_debug_errno(dev, errno, "ioctl(LOOP_SET_FD) failed: %m");
loop_with_fd = TAKE_FD(fd);
@@ -379,14 +383,14 @@ static int loop_configure(
r = fd_get_diskseq(loop_with_fd, &diskseq);
if (r < 0 && r != -EOPNOTSUPP)
return r;
return log_device_debug_errno(dev, r, "Failed to get diskseq: %m");
switch (lock_op & ~LOCK_NB) {
case LOCK_EX: /* Already in effect */
break;
case LOCK_SH: /* Downgrade */
if (flock(lock_fd, lock_op) < 0)
return -errno;
return log_device_debug_errno(dev, errno, "Failed to downgrade lock level: %m");
break;
case LOCK_UN: /* Release */
lock_fd = safe_close(lock_fd);
@@ -397,7 +401,7 @@ static int loop_configure(
LoopDevice *d = new(LoopDevice, 1);
if (!d)
return -ENOMEM;
return log_oom_debug();
*d = (LoopDevice) {
.n_ref = 1,
@@ -549,6 +553,7 @@ static int loop_device_make_internal(
/* Loop around LOOP_CTL_GET_FREE, since at the moment we attempt to open the returned device it might
* be gone already, taken by somebody else racing against us. */
for (unsigned n_attempts = 0;;) {
usec_t usec;
int nr;
/* Let's take a lock on the control device first. On a busy system, where many programs
@@ -590,8 +595,10 @@ static int loop_device_make_internal(
/* Wait some random time, to make collision less likely. Let's pick a random time in the
* range 0ms…250ms, linearly scaled by the number of failed attempts. */
(void) usleep(random_u64_range(UINT64_C(10) * USEC_PER_MSEC +
UINT64_C(240) * USEC_PER_MSEC * n_attempts/64));
usec = random_u64_range(UINT64_C(10) * USEC_PER_MSEC +
UINT64_C(240) * USEC_PER_MSEC * n_attempts/64);
log_debug("Trying again after %s.", FORMAT_TIMESPAN(usec, USEC_PER_MSEC));
(void) usleep(usec);
}
d->backing_file = TAKE_PTR(backing_file);