/* SPDX-License-Identifier: LGPL-2.1-or-later */ #if HAVE_VALGRIND_MEMCHECK_H #include #endif #include #include #include #include #include #include #include #include #include "sd-device.h" #include "alloc-util.h" #include "blockdev-util.h" #include "data-fd-util.h" #include "device-util.h" #include "devnum-util.h" #include "dissect-image.h" #include "env-util.h" #include "errno-util.h" #include "fd-util.h" #include "fs-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; if (ioctl(ASSERT_FD(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 = -EBADF; assert(IN_SET(operation & ~LOCK_NB, LOCK_SH, LOCK_EX)); lock_fd = fd_reopen(ASSERT_FD(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 >= 0); 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) { uint32_t ssz; r = blockdev_get_sector_size(fd, &ssz); if (r < 0) return r; if (ssz != c->block_size) { log_debug("LOOP_CONFIGURE didn't honour requested block size %" PRIu32 ", got %" PRIu32 " instead. Ignoring.", c->block_size, ssz); broken = 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) 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; int r; 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_safe(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"); /* If a block size is requested then try to configure it. If that doesn't work, ignore errors, but * afterwards, let's validate what is in effect, and if it doesn't match what we want, fail */ if (c->block_size != 0) { uint32_t ssz; if (ioctl(fd, LOOP_SET_BLOCK_SIZE, (unsigned long) c->block_size) < 0) log_debug_errno(errno, "Failed to set sector size, ignoring: %m"); r = blockdev_get_sector_size(fd, &ssz); if (r < 0) return log_debug_errno(r, "Failed to read sector size: %m"); if (ssz != c->block_size) return log_debug_errno(SYNTHETIC_ERRNO(EIO), "Sector size of loopback device doesn't match what we requested, refusing."); } /* 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 = -EBADF; /* This must be declared before lock_fd. */ _cleanup_close_ int fd = -EBADF, lock_fd = -EBADF; _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 log_oom_debug(); r = sd_device_new_from_devname(&dev, node); if (r < 0) 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 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 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 * 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 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 log_device_debug_errno(dev, r, "Failed to check if the loopback block device is bound: %m"); if (r > 0) 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 * 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 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 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 * 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 log_device_debug_errno(dev, r, "Failed to get the current uevent seqnum: %m"); 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 log_device_debug_errno(dev, errno, "ioctl(LOOP_CONFIGURE) failed: %m"); loop_configure_broken = true; } else { loop_with_fd = TAKE_FD(fd); r = loop_configure_verify(loop_with_fd, c); if (r < 0) 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; /* 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 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 log_device_debug_errno(dev, errno, "ioctl(LOOP_SET_FD) failed: %m"); 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 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 log_device_debug_errno(dev, errno, "Failed to downgrade lock level: %m"); break; case LOCK_UN: /* Release */ lock_fd = safe_close(lock_fd); break; default: assert_not_reached(); } LoopDevice *d = new(LoopDevice, 1); if (!d) return log_oom_debug(); *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, .sector_size = c->block_size, }; *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 sector_size, uint32_t loop_flags, int lock_op, LoopDevice **ret) { _cleanup_(loop_device_unrefp) LoopDevice *d = NULL; _cleanup_close_ int reopened_fd = -EBADF, control = -EBADF; _cleanup_free_ char *backing_file = NULL; struct loop_config config; int r, f_flags; struct stat st; assert(ret); assert(IN_SET(open_flags, O_RDWR, O_RDONLY)); if (fstat(ASSERT_FD(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; if (sector_size == 0) /* If no sector size is specified, default to the classic default */ sector_size = 512; else if (sector_size == UINT32_MAX) { if (S_ISBLK(st.st_mode)) /* If the sector size is specified as UINT32_MAX we'll propagate the sector size of * the underlying block device. */ r = blockdev_get_sector_size(fd, §or_size); else { _cleanup_close_ int non_direct_io_fd = -EBADF; int probe_fd; assert(S_ISREG(st.st_mode)); /* If sector size is specified as UINT32_MAX, we'll try to probe the right sector * size of the image in question by looking for the GPT partition header at various * offsets. This of course only works if the image already has a disk label. * * So here we actually want to read the file contents ourselves. This is quite likely * not going to work if we managed to enable O_DIRECT, because in such a case there * are some pretty strict alignment requirements to offset, size and target, but * there's no way to query what alignment specifically is actually required. Hence, * let's avoid the mess, and temporarily open an fd without O_DIRECT for the probing * logic. */ if (FLAGS_SET(loop_flags, LO_FLAGS_DIRECT_IO)) { non_direct_io_fd = fd_reopen(fd, O_RDONLY|O_CLOEXEC|O_NONBLOCK); if (non_direct_io_fd < 0) return non_direct_io_fd; probe_fd = non_direct_io_fd; } else probe_fd = fd; r = probe_sector_size(probe_fd, §or_size); } if (r < 0) return r; } config = (struct loop_config) { .fd = fd, .block_size = sector_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;;) { usec_t usec; 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. */ 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_safe(usec); } d->backing_file = TAKE_PTR(backing_file); d->backing_inode = st.st_ino; d->backing_devno = st.st_dev; 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 sector_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, sector_size, loop_flags_mangle(loop_flags), lock_op, ret); } int loop_device_make_by_path_at( int dir_fd, const char *path, int open_flags, uint32_t sector_size, uint32_t loop_flags, int lock_op, LoopDevice **ret) { int r, basic_flags, direct_flags, rdwr_flags; _cleanup_close_ int fd = -EBADF; bool direct = false; assert(dir_fd >= 0 || dir_fd == AT_FDCWD); 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 = xopenat(dir_fd, 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 = xopenat(dir_fd, path, basic_flags|rdwr_flags); else direct = direct_flags != 0; if (fd < 0) { r = fd; /* Retry read-only? */ if (open_flags >= 0 || !(ERRNO_IS_PRIVILEGE(r) || r == -EROFS)) return r; fd = xopenat(dir_fd, path, basic_flags|direct_flags|O_RDONLY); if (fd < 0 && direct_flags != 0) /* as above */ fd = xopenat(dir_fd, 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( dir_fd == AT_FDCWD ? path : NULL, fd, open_flags, /* offset = */ 0, /* size = */ 0, sector_size, loop_flags, lock_op, ret); } int loop_device_make_by_path_memory( const char *path, int open_flags, uint32_t sector_size, uint32_t loop_flags, int lock_op, LoopDevice **ret) { _cleanup_close_ int fd = -EBADF, mfd = -EBADF; _cleanup_free_ char *fn = NULL; struct stat st; int r; assert(path); assert(IN_SET(open_flags, O_RDWR, O_RDONLY)); assert(ret); loop_flags &= ~LO_FLAGS_DIRECT_IO; /* memfds don't support O_DIRECT, hence LO_FLAGS_DIRECT_IO can't be used either */ fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|O_RDONLY); if (fd < 0) return -errno; if (fstat(fd, &st) < 0) return -errno; if (!S_ISREG(st.st_mode) && !S_ISBLK(st.st_mode)) return -EBADF; r = path_extract_filename(path, &fn); if (r < 0) return r; mfd = memfd_clone_fd(fd, fn, open_flags|O_CLOEXEC); if (mfd < 0) return mfd; fd = safe_close(fd); /* Let's close the original early */ return loop_device_make_internal(NULL, mfd, open_flags, 0, 0, sector_size, loop_flags, lock_op, ret); } static LoopDevice* loop_device_free(LoopDevice *d) { _cleanup_close_ int control = -EBADF; 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; /* A total delay of 5090 ms between 39 attempts, * (4*5 + 5*10 + 5*20 + … + 3*640) = 5090. */ 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_safe(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 = -EBADF, lock_fd = -EBADF; _cleanup_free_ char *node = NULL, *backing_file = NULL; dev_t devnum, backing_devno = 0; struct loop_info64 info; ino_t backing_inode = 0; uint64_t diskseq = 0; LoopDevice *d; const char *s; 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; } backing_devno = info.lo_device; backing_inode = info.lo_inode; } r = fd_get_diskseq(fd, &diskseq); if (r < 0 && r != -EOPNOTSUPP) return r; uint32_t sector_size; r = blockdev_get_sector_size(fd, §or_size); if (r < 0) 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), .backing_inode = backing_inode, .backing_devno = backing_devno, .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, .sector_size = sector_size, }; *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; r = block_device_new_from_fd(ASSERT_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 = -EBADF; struct stat st; dev_t devno; int r; /* 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(ASSERT_FD(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, ¤t_offset); if (r < 0) return r; if (current_offset > UINT64_MAX/512U) return -EINVAL; current_offset *= 512U; if (ioctl(partition_fd, BLKGETSIZE64, ¤t_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) { d->lock_fd = open_lock_fd(ASSERT_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); /* 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(ASSERT_FD(d->fd))); } int loop_device_set_autoclear(LoopDevice *d, bool autoclear) { struct loop_info64 info; assert(d); if (ioctl(ASSERT_FD(d->fd), LOOP_GET_STATUS64, &info) < 0) return -errno; if (autoclear == FLAGS_SET(info.lo_flags, LO_FLAGS_AUTOCLEAR)) return 0; SET_FLAG(info.lo_flags, LO_FLAGS_AUTOCLEAR, autoclear); if (ioctl(d->fd, LOOP_SET_STATUS64, &info) < 0) return -errno; return 1; } int loop_device_set_filename(LoopDevice *d, const char *name) { struct loop_info64 info; assert(d); /* Sets the .lo_file_name of the loopback device. This is supposed to contain the path to the file * backing the block device, but is actually just a free-form string you can pass to the kernel. Most * tools that actually care for the backing file path use the sysfs attribute file loop/backing_file * which is a kernel generated string, subject to file system namespaces and such. * * .lo_file_name is useful since userspace can select it freely when creating a loopback block * device, and we can use it for /dev/disk/by-loop-ref/ symlinks, and similar, so that apps can * recognize their own loopback files. */ if (name && strlen(name) >= sizeof(info.lo_file_name)) return -ENOBUFS; if (ioctl(ASSERT_FD(d->fd), LOOP_GET_STATUS64, &info) < 0) return -errno; if (strneq((char*) info.lo_file_name, strempty(name), sizeof(info.lo_file_name))) return 0; if (name) { strncpy((char*) info.lo_file_name, name, sizeof(info.lo_file_name)-1); info.lo_file_name[sizeof(info.lo_file_name)-1] = 0; } else memzero(info.lo_file_name, sizeof(info.lo_file_name)); if (ioctl(d->fd, LOOP_SET_STATUS64, &info) < 0) return -errno; return 1; }