summaryrefslogtreecommitdiffstats
path: root/src/shared/loop-util.c
diff options
context:
space:
mode:
Diffstat (limited to '')
-rw-r--r--src/shared/loop-util.c1027
1 files changed, 1027 insertions, 0 deletions
diff --git a/src/shared/loop-util.c b/src/shared/loop-util.c
new file mode 100644
index 0000000..3396cf5
--- /dev/null
+++ b/src/shared/loop-util.c
@@ -0,0 +1,1027 @@
+/* SPDX-License-Identifier: LGPL-2.1-or-later */
+
+#if HAVE_VALGRIND_MEMCHECK_H
+#include <valgrind/memcheck.h>
+#endif
+
+#include <errno.h>
+#include <fcntl.h>
+#include <linux/blkpg.h>
+#include <linux/fs.h>
+#include <linux/loop.h>
+#include <sys/file.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include "sd-device.h"
+
+#include "alloc-util.h"
+#include "blockdev-util.h"
+#include "device-util.h"
+#include "devnum-util.h"
+#include "env-util.h"
+#include "errno-util.h"
+#include "fd-util.h"
+#include "fileio.h"
+#include "loop-util.h"
+#include "missing_loop.h"
+#include "parse-util.h"
+#include "path-util.h"
+#include "random-util.h"
+#include "stat-util.h"
+#include "stdio-util.h"
+#include "string-util.h"
+#include "tmpfile-util.h"
+
+static void cleanup_clear_loop_close(int *fd) {
+ if (*fd < 0)
+ return;
+
+ (void) ioctl(*fd, LOOP_CLR_FD);
+ (void) safe_close(*fd);
+}
+
+static int loop_is_bound(int fd) {
+ struct loop_info64 info;
+
+ assert(fd >= 0);
+
+ if (ioctl(fd, LOOP_GET_STATUS64, &info) < 0) {
+ if (errno == ENXIO)
+ return false; /* not bound! */
+
+ return -errno;
+ }
+
+ return true; /* bound! */
+}
+
+static int get_current_uevent_seqnum(uint64_t *ret) {
+ _cleanup_free_ char *p = NULL;
+ int r;
+
+ r = read_full_virtual_file("/sys/kernel/uevent_seqnum", &p, NULL);
+ if (r < 0)
+ return log_debug_errno(r, "Failed to read current uevent sequence number: %m");
+
+ r = safe_atou64(strstrip(p), ret);
+ if (r < 0)
+ return log_debug_errno(r, "Failed to parse current uevent sequence number: %s", p);
+
+ return 0;
+}
+
+static int open_lock_fd(int primary_fd, int operation) {
+ _cleanup_close_ int lock_fd = -1;
+
+ assert(primary_fd >= 0);
+ assert(IN_SET(operation & ~LOCK_NB, LOCK_SH, LOCK_EX));
+
+ lock_fd = fd_reopen(primary_fd, O_RDONLY|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
+ if (lock_fd < 0)
+ return lock_fd;
+
+ if (flock(lock_fd, operation) < 0)
+ return -errno;
+
+ return TAKE_FD(lock_fd);
+}
+
+static int loop_configure_verify_direct_io(int fd, const struct loop_config *c) {
+ assert(fd);
+ assert(c);
+
+ if (FLAGS_SET(c->info.lo_flags, LO_FLAGS_DIRECT_IO)) {
+ struct loop_info64 info;
+
+ if (ioctl(fd, LOOP_GET_STATUS64, &info) < 0)
+ return log_debug_errno(errno, "Failed to issue LOOP_GET_STATUS64: %m");
+
+#if HAVE_VALGRIND_MEMCHECK_H
+ VALGRIND_MAKE_MEM_DEFINED(&info, sizeof(info));
+#endif
+
+ /* On older kernels (<= 5.3) it was necessary to set the block size of the loopback block
+ * device to the logical block size of the underlying file system. Since there was no nice
+ * way to query the value, we are not bothering to do this however. On newer kernels the
+ * block size is propagated automatically and does not require intervention from us. We'll
+ * check here if enabling direct IO worked, to make this easily debuggable however.
+ *
+ * (Should anyone really care and actually wants direct IO on old kernels: it might be worth
+ * enabling direct IO with iteratively larger block sizes until it eventually works.)
+ *
+ * On older kernels (e.g.: 5.10) when this is attempted on a file stored on a dm-crypt
+ * backed partition the kernel will start returning I/O errors when accessing the mounted
+ * loop device, so return a recognizable error that causes the operation to be started
+ * from scratch without the LO_FLAGS_DIRECT_IO flag. */
+ if (!FLAGS_SET(info.lo_flags, LO_FLAGS_DIRECT_IO))
+ return log_debug_errno(
+ SYNTHETIC_ERRNO(ENOANO),
+ "Could not enable direct IO mode, retrying in buffered IO mode.");
+ }
+
+ return 0;
+}
+
+static int loop_configure_verify(int fd, const struct loop_config *c) {
+ bool broken = false;
+ int r;
+
+ assert(fd >= 0);
+ assert(c);
+
+ if (c->block_size != 0) {
+ int z;
+
+ if (ioctl(fd, BLKSSZGET, &z) < 0)
+ return -errno;
+
+ assert(z >= 0);
+ if ((uint32_t) z != c->block_size)
+ log_debug("LOOP_CONFIGURE didn't honour requested block size %u, got %i instead. Ignoring.", c->block_size, z);
+ }
+
+ 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)
+ return -errno;
+
+ if (z != c->info.lo_sizelimit) {
+ log_debug("LOOP_CONFIGURE is broken, doesn't honour .info.lo_sizelimit. Falling back to LOOP_SET_STATUS64.");
+ broken = true;
+ }
+ }
+
+ 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)
+ return r;
+ if (r == 0) {
+ log_debug("LOOP_CONFIGURE is broken, doesn't honour LO_FLAGS_PARTSCAN. Falling back to LOOP_SET_STATUS64.");
+ broken = true;
+ }
+ }
+
+ r = loop_configure_verify_direct_io(fd, c);
+ if (r < 0)
+ return r;
+
+ return !broken;
+}
+
+static int loop_configure_fallback(int fd, const struct loop_config *c) {
+ struct loop_info64 info_copy;
+
+ assert(fd >= 0);
+ assert(c);
+
+ /* Only some of the flags LOOP_CONFIGURE can set are also settable via LOOP_SET_STATUS64, hence mask
+ * them out. */
+ info_copy = c->info;
+ info_copy.lo_flags &= LOOP_SET_STATUS_SETTABLE_FLAGS;
+
+ /* Since kernel commit 5db470e229e22b7eda6e23b5566e532c96fb5bc3 (kernel v5.0) the LOOP_SET_STATUS64
+ * ioctl can return EAGAIN in case we change the info.lo_offset field, if someone else is accessing the
+ * block device while we try to reconfigure it. This is a pretty common case, since udev might
+ * instantly start probing the device as soon as we attach an fd to it. Hence handle it in two ways:
+ * first, let's take the BSD lock to ensure that udev will not step in between the point in
+ * time where we attach the fd and where we reconfigure the device. Secondly, let's wait 50ms on
+ * EAGAIN and retry. The former should be an efficient mechanism to avoid we have to wait 50ms
+ * needlessly if we are just racing against udev. The latter is protection against all other cases,
+ * i.e. peers that do not take the BSD lock. */
+
+ for (unsigned n_attempts = 0;;) {
+ if (ioctl(fd, LOOP_SET_STATUS64, &info_copy) >= 0)
+ break;
+
+ if (errno != EAGAIN || ++n_attempts >= 64)
+ return log_debug_errno(errno, "Failed to configure loopback block device: %m");
+
+ /* Sleep some random time, but at least 10ms, at most 250ms. Increase the delay the more
+ * failed attempts we see */
+ (void) usleep(UINT64_C(10) * USEC_PER_MSEC +
+ random_u64_range(UINT64_C(240) * USEC_PER_MSEC * n_attempts/64));
+ }
+
+ /* Work around a kernel bug, where changing offset/size of the loopback device doesn't correctly
+ * invalidate the buffer cache. For details see:
+ *
+ * https://android.googlesource.com/platform/system/apex/+/bef74542fbbb4cd629793f4efee8e0053b360570
+ *
+ * This was fixed in kernel 5.0, see:
+ *
+ * https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=5db470e229e22b7eda6e23b5566e532c96fb5bc3
+ *
+ * We'll run the work-around here in the legacy LOOP_SET_STATUS64 codepath. In the LOOP_CONFIGURE
+ * codepath above it should not be necessary. */
+ if (c->info.lo_offset != 0 || c->info.lo_sizelimit != 0)
+ if (ioctl(fd, BLKFLSBUF, 0) < 0)
+ log_debug_errno(errno, "Failed to issue BLKFLSBUF ioctl, ignoring: %m");
+
+ /* LO_FLAGS_DIRECT_IO is a flags we need to configure via explicit ioctls. */
+ if (FLAGS_SET(c->info.lo_flags, LO_FLAGS_DIRECT_IO))
+ if (ioctl(fd, LOOP_SET_DIRECT_IO, 1UL) < 0)
+ log_debug_errno(errno, "Failed to enable direct IO mode, ignoring: %m");
+
+ return loop_configure_verify_direct_io(fd, c);
+}
+
+static int loop_configure(
+ int nr,
+ int open_flags,
+ int lock_op,
+ const struct loop_config *c,
+ LoopDevice **ret) {
+
+ static bool loop_configure_broken = false;
+
+ _cleanup_(sd_device_unrefp) sd_device *dev = NULL;
+ _cleanup_(cleanup_clear_loop_close) int loop_with_fd = -1; /* This must be declared before lock_fd. */
+ _cleanup_close_ int fd = -1, lock_fd = -1;
+ _cleanup_free_ char *node = NULL;
+ uint64_t diskseq = 0, seqnum = UINT64_MAX;
+ usec_t timestamp = USEC_INFINITY;
+ dev_t devno;
+ int r;
+
+ assert(nr >= 0);
+ assert(c);
+ assert(ret);
+
+ if (asprintf(&node, "/dev/loop%i", nr) < 0)
+ return -ENOMEM;
+
+ r = sd_device_new_from_devname(&dev, node);
+ if (r < 0)
+ return r;
+
+ r = sd_device_get_devnum(dev, &devno);
+ if (r < 0)
+ return r;
+
+ fd = sd_device_open(dev, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
+ if (fd < 0)
+ return fd;
+
+ /* 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
+ * block devices to reprobe them, hence by having a separate fd we will later close() we can ensure
+ * we trigger udev after everything is done. If we'd lock our own fd instead and keep it open for a
+ * long time udev would possibly never run on it again, even though the fd is unlocked, simply
+ * because we never close() it. It also has the nice benefit we can use the _cleanup_close_ logic to
+ * automatically release the lock, after we are done. */
+ lock_fd = open_lock_fd(fd, LOCK_EX);
+ if (lock_fd < 0)
+ return lock_fd;
+
+ /* 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;
+ if (r > 0)
+ return -EBUSY;
+
+ /* 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
+ * superficially is detached but still has partition block devices associated for it. Let's then
+ * manually remove the partitions via BLKPG, and tell the caller we did that via EUCLEAN, so they try
+ * again. */
+ r = block_device_remove_all_partitions(dev, fd);
+ if (r < 0)
+ return r;
+ if (r > 0)
+ /* Removed all partitions. Let's report this to the caller, to try again, and count this as
+ * an attempt. */
+ return -EUCLEAN;
+
+ if (!loop_configure_broken) {
+ /* Acquire uevent seqnum immediately before attaching the loopback device. This allows
+ * callers to ignore all uevents with a seqnum before this one, if they need to associate
+ * uevent with this attachment. Doing so isn't race-free though, as uevents that happen in
+ * the window between this reading of the seqnum, and the LOOP_CONFIGURE call might still be
+ * mistaken as originating from our attachment, even though might be caused by an earlier
+ * use. But doing this at least shortens the race window a bit. */
+ r = get_current_uevent_seqnum(&seqnum);
+ if (r < 0)
+ return r;
+
+ timestamp = now(CLOCK_MONOTONIC);
+
+ if (ioctl(fd, LOOP_CONFIGURE, c) < 0) {
+ /* Do fallback only if LOOP_CONFIGURE is not supported, propagate all other
+ * errors. Note that the kernel is weird: non-existing ioctls currently return EINVAL
+ * 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;
+
+ loop_configure_broken = true;
+ } else {
+ loop_with_fd = TAKE_FD(fd);
+
+ r = loop_configure_verify(loop_with_fd, c);
+ if (r < 0)
+ return r;
+ if (r == 0) {
+ /* LOOP_CONFIGURE doesn't work. Remember that. */
+ loop_configure_broken = true;
+
+ /* We return EBUSY here instead of retrying immediately with LOOP_SET_FD,
+ * because LOOP_CLR_FD is async: if the operation cannot be executed right
+ * away it just sets the autoclear flag on the device. This means there's a
+ * good chance we cannot actually reuse the loopback device right-away. Hence
+ * let's assume it's busy, avoid the trouble and let the calling loop call us
+ * again with a new, likely unused device. */
+ return -EBUSY;
+ }
+ }
+ }
+
+ if (loop_configure_broken) {
+ /* Let's read the seqnum again, to shorten the window. */
+ r = get_current_uevent_seqnum(&seqnum);
+ if (r < 0)
+ return r;
+
+ timestamp = now(CLOCK_MONOTONIC);
+
+ if (ioctl(fd, LOOP_SET_FD, c->fd) < 0)
+ return -errno;
+
+ loop_with_fd = TAKE_FD(fd);
+
+ r = loop_configure_fallback(loop_with_fd, c);
+ if (r < 0)
+ return r;
+ }
+
+ r = fd_get_diskseq(loop_with_fd, &diskseq);
+ if (r < 0 && r != -EOPNOTSUPP)
+ return r;
+
+ 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;
+ break;
+ case LOCK_UN: /* Release */
+ lock_fd = safe_close(lock_fd);
+ break;
+ default:
+ assert_not_reached();
+ }
+
+ LoopDevice *d = new(LoopDevice, 1);
+ if (!d)
+ return -ENOMEM;
+
+ *d = (LoopDevice) {
+ .n_ref = 1,
+ .fd = TAKE_FD(loop_with_fd),
+ .lock_fd = TAKE_FD(lock_fd),
+ .node = TAKE_PTR(node),
+ .nr = nr,
+ .devno = devno,
+ .dev = TAKE_PTR(dev),
+ .diskseq = diskseq,
+ .uevent_seqnum_not_before = seqnum,
+ .timestamp_not_before = timestamp,
+ };
+
+ *ret = TAKE_PTR(d);
+ return 0;
+}
+
+static int loop_device_make_internal(
+ const char *path,
+ int fd,
+ int open_flags,
+ uint64_t offset,
+ uint64_t size,
+ uint32_t block_size,
+ uint32_t loop_flags,
+ int lock_op,
+ LoopDevice **ret) {
+
+ _cleanup_(loop_device_unrefp) LoopDevice *d = NULL;
+ _cleanup_close_ int reopened_fd = -1, control = -1;
+ _cleanup_free_ char *backing_file = NULL;
+ struct loop_config config;
+ int r, f_flags;
+ struct stat st;
+
+ assert(fd >= 0);
+ assert(ret);
+ assert(IN_SET(open_flags, O_RDWR, O_RDONLY));
+
+ if (fstat(fd, &st) < 0)
+ return -errno;
+
+ if (S_ISBLK(st.st_mode)) {
+ if (offset == 0 && IN_SET(size, 0, UINT64_MAX))
+ /* If this is already a block device and we are supposed to cover the whole of it
+ * then store an fd to the original open device node — and do not actually create an
+ * unnecessary loopback device for it. */
+ return loop_device_open_from_fd(fd, open_flags, lock_op, ret);
+ } else {
+ r = stat_verify_regular(&st);
+ if (r < 0)
+ return r;
+ }
+
+ if (path) {
+ r = path_make_absolute_cwd(path, &backing_file);
+ if (r < 0)
+ return r;
+
+ path_simplify(backing_file);
+ } else {
+ r = fd_get_path(fd, &backing_file);
+ if (r < 0)
+ return r;
+ }
+
+ f_flags = fcntl(fd, F_GETFL);
+ if (f_flags < 0)
+ return -errno;
+
+ if (FLAGS_SET(loop_flags, LO_FLAGS_DIRECT_IO) != FLAGS_SET(f_flags, O_DIRECT)) {
+ /* If LO_FLAGS_DIRECT_IO is requested, then make sure we have the fd open with O_DIRECT, as
+ * that's required. Conversely, if it's off require that O_DIRECT is off too (that's because
+ * new kernels will implicitly enable LO_FLAGS_DIRECT_IO if O_DIRECT is set).
+ *
+ * Our intention here is that LO_FLAGS_DIRECT_IO is the primary knob, and O_DIRECT derived
+ * from that automatically. */
+
+ reopened_fd = fd_reopen(fd, (FLAGS_SET(loop_flags, LO_FLAGS_DIRECT_IO) ? O_DIRECT : 0)|O_CLOEXEC|O_NONBLOCK|open_flags);
+ if (reopened_fd < 0) {
+ if (!FLAGS_SET(loop_flags, LO_FLAGS_DIRECT_IO))
+ return log_debug_errno(reopened_fd, "Failed to reopen file descriptor without O_DIRECT: %m");
+
+ /* Some file systems might not support O_DIRECT, let's gracefully continue without it then. */
+ log_debug_errno(reopened_fd, "Failed to enable O_DIRECT for backing file descriptor for loopback device. Continuing without.");
+ loop_flags &= ~LO_FLAGS_DIRECT_IO;
+ } else
+ fd = reopened_fd; /* From now on, operate on our new O_DIRECT fd */
+ }
+
+ control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
+ if (control < 0)
+ return -errno;
+
+ config = (struct loop_config) {
+ .fd = fd,
+ .block_size = block_size,
+ .info = {
+ /* Use the specified flags, but configure the read-only flag from the open flags, and force autoclear */
+ .lo_flags = (loop_flags & ~LO_FLAGS_READ_ONLY) | ((open_flags & O_ACCMODE) == O_RDONLY ? LO_FLAGS_READ_ONLY : 0) | LO_FLAGS_AUTOCLEAR,
+ .lo_offset = offset,
+ .lo_sizelimit = size == UINT64_MAX ? 0 : size,
+ },
+ };
+
+ /* 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;;) {
+ int nr;
+
+ /* Let's take a lock on the control device first. On a busy system, where many programs
+ * attempt to allocate a loopback device at the same time, we might otherwise keep looping
+ * around relatively heavy operations: asking for a free loopback device, then opening it,
+ * validating it, attaching something to it. Let's serialize this whole operation, to make
+ * unnecessary busywork less likely. Note that this is just something we do to optimize our
+ * own code (and whoever else decides to use LOCK_EX locks for this), taking this lock is not
+ * necessary, it just means it's less likely we have to iterate through this loop again and
+ * again if our own code races against our own code.
+ *
+ * Note: our lock protocol is to take the /dev/loop-control lock first, and the block device
+ * lock second, if both are taken, and always in this order, to avoid ABBA locking issues. */
+ if (flock(control, LOCK_EX) < 0)
+ return -errno;
+
+ nr = ioctl(control, LOOP_CTL_GET_FREE);
+ if (nr < 0)
+ return -errno;
+
+ r = loop_configure(nr, open_flags, lock_op, &config, &d);
+ if (r >= 0)
+ break;
+
+ /* -ENODEV or friends: Somebody might've gotten the same number from the kernel, used the
+ * device, and called LOOP_CTL_REMOVE on it. Let's retry with a new number.
+ * -EBUSY: a file descriptor is already bound to the loopback block device.
+ * -EUCLEAN: some left-over partition devices that were cleaned up.
+ * -ENOANO: we tried to use LO_FLAGS_DIRECT_IO but the kernel rejected it. */
+ if (!ERRNO_IS_DEVICE_ABSENT(r) && !IN_SET(r, -EBUSY, -EUCLEAN, -ENOANO))
+ return r;
+
+ /* OK, this didn't work, let's try again a bit later, but first release the lock on the
+ * control device */
+ if (flock(control, LOCK_UN) < 0)
+ return -errno;
+
+ if (++n_attempts >= 64) /* Give up eventually */
+ return -EBUSY;
+
+ /* If we failed to enable direct IO mode, let's retry without it. We restart the process as
+ * on some combination of kernel version and storage filesystem, the kernel is very unhappy
+ * about a failed DIRECT_IO enablement and throws I/O errors. */
+ if (r == -ENOANO && FLAGS_SET(config.info.lo_flags, LO_FLAGS_DIRECT_IO)) {
+ config.info.lo_flags &= ~LO_FLAGS_DIRECT_IO;
+ open_flags &= ~O_DIRECT;
+
+ int non_direct_io_fd = fd_reopen(config.fd, O_CLOEXEC|O_NONBLOCK|open_flags);
+ if (non_direct_io_fd < 0)
+ return log_debug_errno(
+ non_direct_io_fd,
+ "Failed to reopen file descriptor without O_DIRECT: %m");
+
+ safe_close(reopened_fd);
+ fd = config.fd = /* For cleanups */ reopened_fd = non_direct_io_fd;
+ }
+
+ /* 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));
+ }
+
+ d->backing_file = TAKE_PTR(backing_file);
+
+ log_debug("Successfully acquired %s, devno=%u:%u, nr=%i, diskseq=%" PRIu64,
+ d->node,
+ major(d->devno), minor(d->devno),
+ d->nr,
+ d->diskseq);
+
+ *ret = TAKE_PTR(d);
+ return 0;
+}
+
+static uint32_t loop_flags_mangle(uint32_t loop_flags) {
+ int r;
+
+ r = getenv_bool("SYSTEMD_LOOP_DIRECT_IO");
+ if (r < 0 && r != -ENXIO)
+ log_debug_errno(r, "Failed to parse $SYSTEMD_LOOP_DIRECT_IO, ignoring: %m");
+
+ return UPDATE_FLAG(loop_flags, LO_FLAGS_DIRECT_IO, r != 0); /* Turn on LO_FLAGS_DIRECT_IO by default, unless explicitly configured to off. */
+}
+
+int loop_device_make(
+ int fd,
+ int open_flags,
+ uint64_t offset,
+ uint64_t size,
+ uint32_t block_size,
+ uint32_t loop_flags,
+ int lock_op,
+ LoopDevice **ret) {
+
+ assert(fd >= 0);
+ assert(ret);
+
+ return loop_device_make_internal(
+ NULL,
+ fd,
+ open_flags,
+ offset,
+ size,
+ block_size,
+ loop_flags_mangle(loop_flags),
+ lock_op,
+ ret);
+}
+
+int loop_device_make_by_path(
+ const char *path,
+ int open_flags,
+ uint32_t loop_flags,
+ int lock_op,
+ LoopDevice **ret) {
+
+ int r, basic_flags, direct_flags, rdwr_flags;
+ _cleanup_close_ int fd = -1;
+ bool direct = false;
+
+ assert(path);
+ assert(ret);
+ assert(open_flags < 0 || IN_SET(open_flags, O_RDWR, O_RDONLY));
+
+ /* Passing < 0 as open_flags here means we'll try to open the device writable if we can, retrying
+ * read-only if we cannot. */
+
+ loop_flags = loop_flags_mangle(loop_flags);
+
+ /* Let's open with O_DIRECT if we can. But not all file systems support that, hence fall back to
+ * non-O_DIRECT mode automatically, if it fails. */
+
+ basic_flags = O_CLOEXEC|O_NONBLOCK|O_NOCTTY;
+ direct_flags = FLAGS_SET(loop_flags, LO_FLAGS_DIRECT_IO) ? O_DIRECT : 0;
+ rdwr_flags = open_flags >= 0 ? open_flags : O_RDWR;
+
+ fd = open(path, basic_flags|direct_flags|rdwr_flags);
+ if (fd < 0 && direct_flags != 0) /* If we had O_DIRECT on, and things failed with that, let's immediately try again without */
+ fd = open(path, basic_flags|rdwr_flags);
+ else
+ direct = direct_flags != 0;
+ if (fd < 0) {
+ r = -errno;
+
+ /* Retry read-only? */
+ if (open_flags >= 0 || !(ERRNO_IS_PRIVILEGE(r) || r == -EROFS))
+ return r;
+
+ fd = open(path, basic_flags|direct_flags|O_RDONLY);
+ if (fd < 0 && direct_flags != 0) /* as above */
+ fd = open(path, basic_flags|O_RDONLY);
+ else
+ direct = direct_flags != 0;
+ if (fd < 0)
+ return r; /* Propagate original error */
+
+ open_flags = O_RDONLY;
+ } else if (open_flags < 0)
+ open_flags = O_RDWR;
+
+ log_debug("Opened '%s' in %s access mode%s, with O_DIRECT %s%s.",
+ path,
+ open_flags == O_RDWR ? "O_RDWR" : "O_RDONLY",
+ open_flags != rdwr_flags ? " (O_RDWR was requested but not allowed)" : "",
+ direct ? "enabled" : "disabled",
+ direct != (direct_flags != 0) ? " (O_DIRECT was requested but not supported)" : "");
+
+ return loop_device_make_internal(path, fd, open_flags, 0, 0, 0, loop_flags, lock_op, ret);
+}
+
+static LoopDevice* loop_device_free(LoopDevice *d) {
+ _cleanup_close_ int control = -1;
+ int r;
+
+ if (!d)
+ return NULL;
+
+ /* Release any lock we might have on the device first. We want to open+lock the /dev/loop-control
+ * device below, but our lock protocol says that if both control and block device locks are taken,
+ * the control lock needs to be taken first, the block device lock second — in order to avoid ABBA
+ * locking issues. Moreover, we want to issue LOOP_CLR_FD on the block device further down, and that
+ * would fail if we had another fd open to the device. */
+ d->lock_fd = safe_close(d->lock_fd);
+
+ /* Let's open the control device early, and lock it, so that we can release our block device and
+ * delete it in a synchronized fashion, and allocators won't needlessly see the block device as free
+ * while we are about to delete it. */
+ if (!LOOP_DEVICE_IS_FOREIGN(d) && !d->relinquished) {
+ control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
+ if (control < 0)
+ log_debug_errno(errno, "Failed to open loop control device, cannot remove loop device '%s', ignoring: %m", strna(d->node));
+ else if (flock(control, LOCK_EX) < 0)
+ log_debug_errno(errno, "Failed to lock loop control device, ignoring: %m");
+ }
+
+ /* Then let's release the loopback block device */
+ if (d->fd >= 0) {
+ /* Implicitly sync the device, since otherwise in-flight blocks might not get written */
+ if (fsync(d->fd) < 0)
+ log_debug_errno(errno, "Failed to sync loop block device, ignoring: %m");
+
+ if (!LOOP_DEVICE_IS_FOREIGN(d) && !d->relinquished) {
+ /* We are supposed to clear the loopback device. Let's do this synchronously: lock
+ * the device, manually remove all partitions and then clear it. This should ensure
+ * udev doesn't concurrently access the devices, and we can be reasonably sure that
+ * once we are done here the device is cleared and all its partition children
+ * removed. Note that we lock our primary device fd here (and not a separate locking
+ * fd, as we do during allocation, since we want to keep the lock all the way through
+ * the LOOP_CLR_FD, but that call would fail if we had more than one fd open.) */
+
+ if (flock(d->fd, LOCK_EX) < 0)
+ log_debug_errno(errno, "Failed to lock loop block device, ignoring: %m");
+
+ r = block_device_remove_all_partitions(d->dev, d->fd);
+ if (r < 0)
+ log_debug_errno(r, "Failed to remove partitions of loopback block device, ignoring: %m");
+
+ if (ioctl(d->fd, LOOP_CLR_FD) < 0)
+ log_debug_errno(errno, "Failed to clear loop device, ignoring: %m");
+ }
+
+ safe_close(d->fd);
+ }
+
+ /* Now that the block device is released, let's also try to remove it */
+ if (control >= 0) {
+ useconds_t delay = 5 * USEC_PER_MSEC;
+
+ for (unsigned attempt = 1;; attempt++) {
+ if (ioctl(control, LOOP_CTL_REMOVE, d->nr) >= 0)
+ break;
+ if (errno != EBUSY || attempt > 38) {
+ log_debug_errno(errno, "Failed to remove device %s: %m", strna(d->node));
+ break;
+ }
+ if (attempt % 5 == 0) {
+ log_debug("Device is still busy after %u attempts…", attempt);
+ delay *= 2;
+ }
+
+ (void) usleep(delay);
+ }
+ }
+
+ free(d->node);
+ sd_device_unref(d->dev);
+ free(d->backing_file);
+ return mfree(d);
+}
+
+DEFINE_TRIVIAL_REF_UNREF_FUNC(LoopDevice, loop_device, loop_device_free);
+
+void loop_device_relinquish(LoopDevice *d) {
+ assert(d);
+
+ /* Don't attempt to clean up the loop device anymore from this point on. Leave the clean-ing up to the kernel
+ * itself, using the loop device "auto-clear" logic we already turned on when creating the device. */
+
+ d->relinquished = true;
+}
+
+void loop_device_unrelinquish(LoopDevice *d) {
+ assert(d);
+ d->relinquished = false;
+}
+
+int loop_device_open(
+ sd_device *dev,
+ int open_flags,
+ int lock_op,
+ LoopDevice **ret) {
+
+ _cleanup_close_ int fd = -1, lock_fd = -1;
+ _cleanup_free_ char *node = NULL, *backing_file = NULL;
+ struct loop_info64 info;
+ uint64_t diskseq = 0;
+ LoopDevice *d;
+ const char *s;
+ dev_t devnum;
+ int r, nr = -1;
+
+ assert(dev);
+ assert(IN_SET(open_flags, O_RDWR, O_RDONLY));
+ assert(ret);
+
+ /* Even if fd is provided through the argument in loop_device_open_from_fd(), we reopen the inode
+ * here, instead of keeping just a dup() clone of it around, since we want to ensure that the
+ * O_DIRECT flag of the handle we keep is off, we have our own file index, and have the right
+ * read/write mode in effect. */
+ fd = sd_device_open(dev, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
+ if (fd < 0)
+ return fd;
+
+ if ((lock_op & ~LOCK_NB) != LOCK_UN) {
+ lock_fd = open_lock_fd(fd, lock_op);
+ if (lock_fd < 0)
+ return lock_fd;
+ }
+
+ if (ioctl(fd, LOOP_GET_STATUS64, &info) >= 0) {
+#if HAVE_VALGRIND_MEMCHECK_H
+ /* Valgrind currently doesn't know LOOP_GET_STATUS64. Remove this once it does */
+ VALGRIND_MAKE_MEM_DEFINED(&info, sizeof(info));
+#endif
+ nr = info.lo_number;
+
+ if (sd_device_get_sysattr_value(dev, "loop/backing_file", &s) >= 0) {
+ backing_file = strdup(s);
+ if (!backing_file)
+ return -ENOMEM;
+ }
+ }
+
+ r = fd_get_diskseq(fd, &diskseq);
+ if (r < 0 && r != -EOPNOTSUPP)
+ return r;
+
+ r = sd_device_get_devnum(dev, &devnum);
+ if (r < 0)
+ return r;
+
+ r = sd_device_get_devname(dev, &s);
+ if (r < 0)
+ return r;
+
+ node = strdup(s);
+ if (!node)
+ return -ENOMEM;
+
+ d = new(LoopDevice, 1);
+ if (!d)
+ return -ENOMEM;
+
+ *d = (LoopDevice) {
+ .n_ref = 1,
+ .fd = TAKE_FD(fd),
+ .lock_fd = TAKE_FD(lock_fd),
+ .nr = nr,
+ .node = TAKE_PTR(node),
+ .dev = sd_device_ref(dev),
+ .backing_file = TAKE_PTR(backing_file),
+ .relinquished = true, /* It's not ours, don't try to destroy it when this object is freed */
+ .devno = devnum,
+ .diskseq = diskseq,
+ .uevent_seqnum_not_before = UINT64_MAX,
+ .timestamp_not_before = USEC_INFINITY,
+ };
+
+ *ret = d;
+ return 0;
+}
+
+int loop_device_open_from_fd(
+ int fd,
+ int open_flags,
+ int lock_op,
+ LoopDevice **ret) {
+
+ _cleanup_(sd_device_unrefp) sd_device *dev = NULL;
+ int r;
+
+ assert(fd >= 0);
+
+ r = block_device_new_from_fd(fd, 0, &dev);
+ if (r < 0)
+ return r;
+
+ return loop_device_open(dev, open_flags, lock_op, ret);
+}
+
+int loop_device_open_from_path(
+ const char *path,
+ int open_flags,
+ int lock_op,
+ LoopDevice **ret) {
+
+ _cleanup_(sd_device_unrefp) sd_device *dev = NULL;
+ int r;
+
+ assert(path);
+
+ r = block_device_new_from_path(path, 0, &dev);
+ if (r < 0)
+ return r;
+
+ return loop_device_open(dev, open_flags, lock_op, ret);
+}
+
+static int resize_partition(int partition_fd, uint64_t offset, uint64_t size) {
+ char sysfs[STRLEN("/sys/dev/block/:/partition") + 2*DECIMAL_STR_MAX(dev_t) + 1];
+ _cleanup_free_ char *buffer = NULL;
+ uint64_t current_offset, current_size, partno;
+ _cleanup_close_ int whole_fd = -1;
+ struct stat st;
+ dev_t devno;
+ int r;
+
+ assert(partition_fd >= 0);
+
+ /* Resizes the partition the loopback device refer to (assuming it refers to one instead of an actual
+ * loopback device), and changes the offset, if needed. This is a fancy wrapper around
+ * BLKPG_RESIZE_PARTITION. */
+
+ if (fstat(partition_fd, &st) < 0)
+ return -errno;
+
+ assert(S_ISBLK(st.st_mode));
+
+ xsprintf(sysfs, "/sys/dev/block/" DEVNUM_FORMAT_STR "/partition", DEVNUM_FORMAT_VAL(st.st_rdev));
+ r = read_one_line_file(sysfs, &buffer);
+ if (r == -ENOENT) /* not a partition, cannot resize */
+ return -ENOTTY;
+ if (r < 0)
+ return r;
+ r = safe_atou64(buffer, &partno);
+ if (r < 0)
+ return r;
+
+ xsprintf(sysfs, "/sys/dev/block/" DEVNUM_FORMAT_STR "/start", DEVNUM_FORMAT_VAL(st.st_rdev));
+
+ buffer = mfree(buffer);
+ r = read_one_line_file(sysfs, &buffer);
+ if (r < 0)
+ return r;
+ r = safe_atou64(buffer, &current_offset);
+ if (r < 0)
+ return r;
+ if (current_offset > UINT64_MAX/512U)
+ return -EINVAL;
+ current_offset *= 512U;
+
+ if (ioctl(partition_fd, BLKGETSIZE64, &current_size) < 0)
+ return -EINVAL;
+
+ if (size == UINT64_MAX && offset == UINT64_MAX)
+ return 0;
+ if (current_size == size && current_offset == offset)
+ return 0;
+
+ xsprintf(sysfs, "/sys/dev/block/" DEVNUM_FORMAT_STR "/../dev", DEVNUM_FORMAT_VAL(st.st_rdev));
+
+ buffer = mfree(buffer);
+ r = read_one_line_file(sysfs, &buffer);
+ if (r < 0)
+ return r;
+ r = parse_devnum(buffer, &devno);
+ if (r < 0)
+ return r;
+
+ whole_fd = r = device_open_from_devnum(S_IFBLK, devno, O_RDWR|O_CLOEXEC|O_NONBLOCK|O_NOCTTY, NULL);
+ if (r < 0)
+ return r;
+
+ return block_device_resize_partition(
+ whole_fd,
+ partno,
+ offset == UINT64_MAX ? current_offset : offset,
+ size == UINT64_MAX ? current_size : size);
+}
+
+int loop_device_refresh_size(LoopDevice *d, uint64_t offset, uint64_t size) {
+ struct loop_info64 info;
+
+ assert(d);
+ assert(d->fd >= 0);
+
+ /* Changes the offset/start of the loop device relative to the beginning of the underlying file or
+ * block device. If this loop device actually refers to a partition and not a loopback device, we'll
+ * try to adjust the partition offsets instead.
+ *
+ * If either offset or size is UINT64_MAX we won't change that parameter. */
+
+ if (d->nr < 0) /* not a loopback device */
+ return resize_partition(d->fd, offset, size);
+
+ if (ioctl(d->fd, LOOP_GET_STATUS64, &info) < 0)
+ return -errno;
+
+#if HAVE_VALGRIND_MEMCHECK_H
+ /* Valgrind currently doesn't know LOOP_GET_STATUS64. Remove this once it does */
+ VALGRIND_MAKE_MEM_DEFINED(&info, sizeof(info));
+#endif
+
+ if (size == UINT64_MAX && offset == UINT64_MAX)
+ return 0;
+ if (info.lo_sizelimit == size && info.lo_offset == offset)
+ return 0;
+
+ if (size != UINT64_MAX)
+ info.lo_sizelimit = size;
+ if (offset != UINT64_MAX)
+ info.lo_offset = offset;
+
+ return RET_NERRNO(ioctl(d->fd, LOOP_SET_STATUS64, &info));
+}
+
+int loop_device_flock(LoopDevice *d, int operation) {
+ assert(IN_SET(operation & ~LOCK_NB, LOCK_UN, LOCK_SH, LOCK_EX));
+ assert(d);
+
+ /* When unlocking just close the lock fd */
+ if ((operation & ~LOCK_NB) == LOCK_UN) {
+ d->lock_fd = safe_close(d->lock_fd);
+ return 0;
+ }
+
+ /* If we had no lock fd so far, create one and lock it right-away */
+ if (d->lock_fd < 0) {
+ assert(d->fd >= 0);
+
+ d->lock_fd = open_lock_fd(d->fd, operation);
+ if (d->lock_fd < 0)
+ return d->lock_fd;
+
+ return 0;
+ }
+
+ /* Otherwise change the current lock mode on the existing fd */
+ return RET_NERRNO(flock(d->lock_fd, operation));
+}
+
+int loop_device_sync(LoopDevice *d) {
+ assert(d);
+ assert(d->fd >= 0);
+
+ /* We also do this implicitly in loop_device_unref(). Doing this explicitly here has the benefit that
+ * we can check the return value though. */
+
+ return RET_NERRNO(fsync(d->fd));
+}