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Systemd/src/shared/loop-util.c

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/* SPDX-License-Identifier: LGPL-2.1+ */
#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 "errno-util.h"
#include "fd-util.h"
#include "fileio.h"
#include "loop-util.h"
#include "missing_loop.h"
#include "parse-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 device_has_block_children(sd_device *d) {
_cleanup_(sd_device_enumerator_unrefp) sd_device_enumerator *e = NULL;
const char *main_sn, *main_ss;
sd_device *q;
int r;
assert(d);
/* Checks if the specified device currently has block device children (i.e. partition block
* devices). */
r = sd_device_get_sysname(d, &main_sn);
if (r < 0)
return r;
r = sd_device_get_subsystem(d, &main_ss);
if (r < 0)
return r;
if (!streq(main_ss, "block"))
return -EINVAL;
r = sd_device_enumerator_new(&e);
if (r < 0)
return r;
r = sd_device_enumerator_allow_uninitialized(e);
if (r < 0)
return r;
r = sd_device_enumerator_add_match_parent(e, d);
if (r < 0)
return r;
FOREACH_DEVICE(e, q) {
const char *ss, *sn;
r = sd_device_get_subsystem(q, &ss);
if (r < 0)
continue;
if (!streq(ss, "block"))
continue;
r = sd_device_get_sysname(q, &sn);
if (r < 0)
continue;
if (streq(sn, main_sn))
continue;
return 1; /* we have block device children */
}
return 0;
}
static int loop_configure(
int fd,
int nr,
const struct loop_config *c,
bool *try_loop_configure) {
_cleanup_(sd_device_unrefp) sd_device *d = NULL;
_cleanup_free_ char *sysname = NULL;
_cleanup_close_ int lock_fd = -1;
int r;
assert(fd >= 0);
assert(nr >= 0);
assert(c);
assert(try_loop_configure);
if (asprintf(&sysname, "loop%i", nr) < 0)
return -ENOMEM;
r = sd_device_new_from_subsystem_sysname(&d, "block", sysname);
if (r < 0)
return r;
/* 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 = fd_reopen(fd, O_RDWR|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
if (lock_fd < 0)
return lock_fd;
if (flock(lock_fd, LOCK_EX) < 0)
return -errno;
/* 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. They only go
* away when the device is reattached. (Yes, LOOP_CLR_FD doesn't work then, because officially
* nothing is attached and LOOP_CTL_REMOVE doesn't either, since it doesn't care about partition
* block devices. */
r = device_has_block_children(d);
if (r < 0)
return r;
if (r > 0) {
r = loop_is_bound(fd);
if (r < 0)
return r;
if (r > 0)
return -EBUSY;
return -EUCLEAN; /* Bound but children? Tell caller to reattach something so that the
* partition block devices are gone too. */
}
if (*try_loop_configure) {
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;
*try_loop_configure = false;
} else {
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) {
/* LOOP_CONFIGURE doesn't work. Remember that. */
*try_loop_configure = false;
/* 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. */
r = -EBUSY;
goto fail;
}
return 0;
}
}
/* Since kernel commit 5db470e229e22b7eda6e23b5566e532c96fb5bc3 (kernel v5.0) the LOOP_SET_STATUS64
* ioctl can return EAGAIN in case we change the 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 that that ensures 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. */
if (ioctl(fd, LOOP_SET_FD, c->fd) < 0)
return -errno;
for (unsigned n_attempts = 0;;) {
if (ioctl(fd, LOOP_SET_STATUS64, &c->info) >= 0)
break;
if (errno != EAGAIN || ++n_attempts >= 64) {
r = log_debug_errno(errno, "Failed to configure loopback device: %m");
goto fail;
}
/* 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() % (UINT64_C(240) * USEC_PER_MSEC * n_attempts/64));
}
return 0;
fail:
(void) ioctl(fd, LOOP_CLR_FD);
return r;
}
static int attach_empty_file(int loop, int nr) {
_cleanup_close_ int fd = -1;
/* So here's the thing: on various kernels (5.8 at least) loop block devices might enter a state
* where they are detached but nonetheless have partitions, when used heavily. Accessing these
* partitions results in immediatey IO errors. There's no pretty way to get rid of them
* again. Neither LOOP_CLR_FD nor LOOP_CTL_REMOVE suffice (see above). What does work is to
* reassociate them with a new fd however. This is what we do here hence: we associate the devices
* with an empty file (i.e. an image that definitely has no partitions). We then immediately clear it
* again. This suffices to make the partitions go away. Ugly but appears to work. */
log_debug("Found unattached loopback block device /dev/loop%i with partitions. Attaching empty file to remove them.", nr);
fd = open_tmpfile_unlinkable(NULL, O_RDONLY);
if (fd < 0)
return fd;
if (flock(loop, LOCK_EX) < 0)
return -errno;
if (ioctl(loop, LOOP_SET_FD, fd) < 0)
return -errno;
if (ioctl(loop, LOOP_SET_STATUS64, &(struct loop_info64) {
.lo_flags = LO_FLAGS_READ_ONLY|
LO_FLAGS_AUTOCLEAR|
LO_FLAGS_PARTSCAN, /* enable partscan, so that the partitions really go away */
}) < 0)
return -errno;
if (ioctl(loop, LOOP_CLR_FD) < 0)
return -errno;
/* The caller is expected to immediately close the loopback device after this, so that the BSD lock
* is released, and udev sees the changes. */
return 0;
}
int loop_device_make(
int fd,
int open_flags,
uint64_t offset,
uint64_t size,
uint32_t loop_flags,
LoopDevice **ret) {
_cleanup_free_ char *loopdev = NULL;
bool try_loop_configure = true;
struct loop_config config;
LoopDevice *d = NULL;
struct stat st;
int nr = -1, r;
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 (ioctl(fd, LOOP_GET_STATUS64, &config.info) >= 0) {
/* Oh! This is a loopback device? That's interesting! */
#if HAVE_VALGRIND_MEMCHECK_H
/* Valgrind currently doesn't know LOOP_GET_STATUS64. Remove this once it does */
VALGRIND_MAKE_MEM_DEFINED(&config.info, sizeof(config.info));
#endif
nr = config.info.lo_number;
if (asprintf(&loopdev, "/dev/loop%i", nr) < 0)
return -ENOMEM;
}
if (offset == 0 && IN_SET(size, 0, UINT64_MAX)) {
_cleanup_close_ int copy = -1;
/* If this is already a block device, store a copy of the fd as it is */
copy = fcntl(fd, F_DUPFD_CLOEXEC, 3);
if (copy < 0)
return -errno;
d = new(LoopDevice, 1);
if (!d)
return -ENOMEM;
*d = (LoopDevice) {
.fd = TAKE_FD(copy),
.nr = nr,
.node = TAKE_PTR(loopdev),
.relinquished = true, /* It's not allocated by us, don't destroy it when this object is freed */
};
*ret = d;
return d->fd;
}
} else {
r = stat_verify_regular(&st);
if (r < 0)
return r;
}
_cleanup_close_ int control = -1;
_cleanup_(cleanup_clear_loop_close) int loop_with_fd = -1;
control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
if (control < 0)
return -errno;
config = (struct loop_config) {
.fd = fd,
.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;;) {
_cleanup_close_ int loop = -1;
nr = ioctl(control, LOOP_CTL_GET_FREE);
if (nr < 0)
return -errno;
if (asprintf(&loopdev, "/dev/loop%i", nr) < 0)
return -ENOMEM;
loop = open(loopdev, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
if (loop < 0) {
/* 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. */
if (!IN_SET(errno, ENOENT, ENXIO))
return -errno;
} else {
r = loop_configure(loop, nr, &config, &try_loop_configure);
if (r >= 0) {
loop_with_fd = TAKE_FD(loop);
break;
}
if (r == -EUCLEAN) {
/* Make left-over partition disappear hack (see above) */
r = attach_empty_file(loop, nr);
if (r < 0 && r != -EBUSY)
return r;
} else if (r != -EBUSY)
return r;
}
if (++n_attempts >= 64) /* Give up eventually */
return -EBUSY;
loopdev = mfree(loopdev);
/* 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() % (UINT64_C(10) * USEC_PER_MSEC +
UINT64_C(240) * USEC_PER_MSEC * n_attempts/64));
}
d = new(LoopDevice, 1);
if (!d)
return -ENOMEM;
*d = (LoopDevice) {
.fd = TAKE_FD(loop_with_fd),
.node = TAKE_PTR(loopdev),
.nr = nr,
};
*ret = d;
return 0;
}
int loop_device_make_by_path(const char *path, int open_flags, uint32_t loop_flags, LoopDevice **ret) {
_cleanup_close_ int fd = -1;
int r;
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. */
fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|(open_flags >= 0 ? open_flags : O_RDWR));
if (fd < 0) {
r = -errno;
/* Retry read-only? */
if (open_flags >= 0 || !(ERRNO_IS_PRIVILEGE(r) || r == -EROFS))
return r;
fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|O_RDONLY);
if (fd < 0)
return r; /* Propagate original error */
open_flags = O_RDONLY;
} else if (open_flags < 0)
open_flags = O_RDWR;
return loop_device_make(fd, open_flags, 0, 0, loop_flags, ret);
}
LoopDevice* loop_device_unref(LoopDevice *d) {
if (!d)
return NULL;
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 (d->nr >= 0 && !d->relinquished) {
if (ioctl(d->fd, LOOP_CLR_FD) < 0)
log_debug_errno(errno, "Failed to clear loop device: %m");
}
safe_close(d->fd);
}
if (d->nr >= 0 && !d->relinquished) {
_cleanup_close_ int control = -1;
control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
if (control < 0)
log_warning_errno(errno,
"Failed to open loop control device, cannot remove loop device %s: %m",
strna(d->node));
else
for (unsigned n_attempts = 0;;) {
if (ioctl(control, LOOP_CTL_REMOVE, d->nr) >= 0)
break;
if (errno != EBUSY || ++n_attempts >= 64) {
log_warning_errno(errno, "Failed to remove device %s: %m", strna(d->node));
break;
}
(void) usleep(50 * USEC_PER_MSEC);
}
}
free(d->node);
return mfree(d);
}
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;
}
int loop_device_open(const char *loop_path, int open_flags, LoopDevice **ret) {
_cleanup_close_ int loop_fd = -1;
_cleanup_free_ char *p = NULL;
struct loop_info64 info;
struct stat st;
LoopDevice *d;
int nr;
assert(loop_path);
assert(ret);
loop_fd = open(loop_path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
if (loop_fd < 0)
return -errno;
if (fstat(loop_fd, &st) < 0)
return -errno;
if (!S_ISBLK(st.st_mode))
return -ENOTBLK;
if (ioctl(loop_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;
} else
nr = -1;
p = strdup(loop_path);
if (!p)
return -ENOMEM;
d = new(LoopDevice, 1);
if (!d)
return -ENOMEM;
*d = (LoopDevice) {
.fd = TAKE_FD(loop_fd),
.nr = nr,
.node = TAKE_PTR(p),
.relinquished = true, /* It's not ours, don't try to destroy it when this object is freed */
};
*ret = d;
return d->fd;
}
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 *whole = NULL, *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/%u:%u/partition", major(st.st_rdev), minor(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/%u:%u/start", major(st.st_rdev), minor(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/%u:%u/../dev", major(st.st_rdev), minor(st.st_rdev));
buffer = mfree(buffer);
r = read_one_line_file(sysfs, &buffer);
if (r < 0)
return r;
r = parse_dev(buffer, &devno);
if (r < 0)
return r;
r = device_path_make_major_minor(S_IFBLK, devno, &whole);
if (r < 0)
return r;
whole_fd = open(whole, O_RDWR|O_CLOEXEC|O_NONBLOCK|O_NOCTTY);
if (whole_fd < 0)
return -errno;
struct blkpg_partition bp = {
.pno = partno,
.start = offset == UINT64_MAX ? current_offset : offset,
.length = size == UINT64_MAX ? current_size : size,
};
struct blkpg_ioctl_arg ba = {
.op = BLKPG_RESIZE_PARTITION,
.data = &bp,
.datalen = sizeof(bp),
};
if (ioctl(whole_fd, BLKPG, &ba) < 0)
return -errno;
return 0;
}
int loop_device_refresh_size(LoopDevice *d, uint64_t offset, uint64_t size) {
struct loop_info64 info;
assert(d);
/* 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->fd < 0)
return -EBADF;
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;
if (ioctl(d->fd, LOOP_SET_STATUS64, &info) < 0)
return -errno;
return 0;
}
int loop_device_flock(LoopDevice *d, int operation) {
assert(d);
if (d->fd < 0)
return -EBADF;
if (flock(d->fd, operation) < 0)
return -errno;
return 0;
}
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. */
if (d->fd < 0)
return -EBADF;
if (fsync(d->fd) < 0)
return -errno;
return 0;
}
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