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Merge pull request #30064 from bluca/unbork_direct_io
loop-util: restart loop_configure and reopen FD when O_DIRECT fails
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commit
41113e1c10
@ -108,9 +108,16 @@ static int loop_configure_verify_direct_io(int fd, const struct loop_config *c)
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* check here if enabling direct IO worked, to make this easily debuggable however.
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*
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* (Should anyone really care and actually wants direct IO on old kernels: it might be worth
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* enabling direct IO with iteratively larger block sizes until it eventually works.) */
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* enabling direct IO with iteratively larger block sizes until it eventually works.)
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*
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* On older kernels (e.g.: 5.10) when this is attempted on a file stored on a dm-crypt
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* backed partition the kernel will start returning I/O errors when accessing the mounted
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* loop device, so return a recognizable error that causes the operation to be started
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* from scratch without the LO_FLAGS_DIRECT_IO flag. */
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if (!FLAGS_SET(info.lo_flags, LO_FLAGS_DIRECT_IO))
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log_debug("Could not enable direct IO mode, proceeding in buffered IO mode.");
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return log_debug_errno(
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SYNTHETIC_ERRNO(ENOANO),
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"Could not enable direct IO mode, retrying in buffered IO mode.");
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}
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return 0;
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@ -431,7 +438,7 @@ static int loop_device_make_internal(
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LoopDevice **ret) {
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_cleanup_(loop_device_unrefp) LoopDevice *d = NULL;
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_cleanup_close_ int direct_io_fd = -EBADF, control = -EBADF;
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_cleanup_close_ int reopened_fd = -EBADF, control = -EBADF;
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_cleanup_free_ char *backing_file = NULL;
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struct loop_config config;
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int r, f_flags;
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@ -479,16 +486,16 @@ static int loop_device_make_internal(
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* Our intention here is that LO_FLAGS_DIRECT_IO is the primary knob, and O_DIRECT derived
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* from that automatically. */
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direct_io_fd = fd_reopen(fd, (FLAGS_SET(loop_flags, LO_FLAGS_DIRECT_IO) ? O_DIRECT : 0)|O_CLOEXEC|O_NONBLOCK|open_flags);
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if (direct_io_fd < 0) {
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reopened_fd = fd_reopen(fd, (FLAGS_SET(loop_flags, LO_FLAGS_DIRECT_IO) ? O_DIRECT : 0)|O_CLOEXEC|O_NONBLOCK|open_flags);
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if (reopened_fd < 0) {
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if (!FLAGS_SET(loop_flags, LO_FLAGS_DIRECT_IO))
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return log_debug_errno(errno, "Failed to reopen file descriptor without O_DIRECT: %m");
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return log_debug_errno(reopened_fd, "Failed to reopen file descriptor without O_DIRECT: %m");
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/* Some file systems might not support O_DIRECT, let's gracefully continue without it then. */
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log_debug_errno(errno, "Failed to enable O_DIRECT for backing file descriptor for loopback device. Continuing without.");
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log_debug_errno(reopened_fd, "Failed to enable O_DIRECT for backing file descriptor for loopback device. Continuing without.");
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loop_flags &= ~LO_FLAGS_DIRECT_IO;
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} else
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fd = direct_io_fd; /* From now on, operate on our new O_DIRECT fd */
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fd = reopened_fd; /* From now on, operate on our new O_DIRECT fd */
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}
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control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
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@ -578,8 +585,9 @@ static int loop_device_make_internal(
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/* -ENODEV or friends: Somebody might've gotten the same number from the kernel, used the
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* device, and called LOOP_CTL_REMOVE on it. Let's retry with a new number.
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* -EBUSY: a file descriptor is already bound to the loopback block device.
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* -EUCLEAN: some left-over partition devices that were cleaned up. */
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if (!ERRNO_IS_DEVICE_ABSENT(r) && !IN_SET(r, -EBUSY, -EUCLEAN))
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* -EUCLEAN: some left-over partition devices that were cleaned up.
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* -ENOANO: we tried to use LO_FLAGS_DIRECT_IO but the kernel rejected it. */
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if (!ERRNO_IS_DEVICE_ABSENT(r) && !IN_SET(r, -EBUSY, -EUCLEAN, -ENOANO))
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return r;
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/* OK, this didn't work, let's try again a bit later, but first release the lock on the
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@ -590,6 +598,23 @@ static int loop_device_make_internal(
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if (++n_attempts >= 64) /* Give up eventually */
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return -EBUSY;
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/* If we failed to enable direct IO mode, let's retry without it. We restart the process as
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* on some combination of kernel version and storage filesystem, the kernel is very unhappy
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* about a failed DIRECT_IO enablement and throws I/O errors. */
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if (r == -ENOANO && FLAGS_SET(config.info.lo_flags, LO_FLAGS_DIRECT_IO)) {
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config.info.lo_flags &= ~LO_FLAGS_DIRECT_IO;
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open_flags &= ~O_DIRECT;
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int non_direct_io_fd = fd_reopen(config.fd, O_CLOEXEC|O_NONBLOCK|open_flags);
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if (non_direct_io_fd < 0)
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return log_debug_errno(
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non_direct_io_fd,
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"Failed to reopen file descriptor without O_DIRECT: %m");
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safe_close(reopened_fd);
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fd = config.fd = /* For cleanups */ reopened_fd = non_direct_io_fd;
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}
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/* Wait some random time, to make collision less likely. Let's pick a random time in the
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* range 0ms…250ms, linearly scaled by the number of failed attempts. */
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usec = random_u64_range(UINT64_C(10) * USEC_PER_MSEC +
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