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/* SPDX-License-Identifier: LGPL-2.1+ */
#include <errno.h>
#include <fcntl.h>
#include <linux/loop.h>
#include <sys/ioctl.h>
#include <sys/stat.h>
#include "alloc-util.h"
#include "fd-util.h"
#include "loop-util.h"
#include "stat-util.h"
int loop_device_make(int fd, int open_flags, LoopDevice **ret) {
const struct loop_info64 info = {
.lo_flags = LO_FLAGS_AUTOCLEAR|LO_FLAGS_PARTSCAN|(open_flags == O_RDONLY ? LO_FLAGS_READ_ONLY : 0),
};
_cleanup_close_ int control = -1, loop = -1;
_cleanup_free_ char *loopdev = NULL;
unsigned n_attempts = 0;
struct stat st;
LoopDevice *d;
int nr, 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)) {
int copy;
/* 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 = new0(LoopDevice, 1);
if (!d)
return -ENOMEM;
*d = (LoopDevice) {
.fd = copy,
.nr = -1,
.relinquished = true, /* It's not allocated by us, don't destroy it when this object is freed */
};
*ret = d;
return d->fd;
}
r = stat_verify_regular(&st);
if (r < 0)
return r;
control = open("/dev/loop-control", O_RDWR|O_CLOEXEC|O_NOCTTY|O_NONBLOCK);
if (control < 0)
return -errno;
/* 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 (;;) {
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)
return -errno;
if (ioctl(loop, LOOP_SET_FD, fd) < 0) {
if (errno != EBUSY)
return -errno;
if (++n_attempts >= 64) /* Give up eventually */
return -EBUSY;
} else
break;
loopdev = mfree(loopdev);
loop = safe_close(loop);
}
if (ioctl(loop, LOOP_SET_STATUS64, &info) < 0)
return -errno;
d = new(LoopDevice, 1);
if (!d)
return -ENOMEM;
*d = (LoopDevice) {
.fd = TAKE_FD(loop),
.node = TAKE_PTR(loopdev),
.nr = nr,
};
*ret = d;
return d->fd;
}
int loop_device_make_by_path(const char *path, int open_flags, LoopDevice **ret) {
_cleanup_close_ int fd = -1;
assert(path);
assert(ret);
assert(IN_SET(open_flags, O_RDWR, O_RDONLY));
fd = open(path, O_CLOEXEC|O_NONBLOCK|O_NOCTTY|open_flags);
if (fd < 0)
return -errno;
return loop_device_make(fd, open_flags, ret);
}
LoopDevice* loop_device_unref(LoopDevice *d) {
if (!d)
return NULL;
if (d->fd >= 0) {
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_debug_errno(errno, "Failed to open loop control device: %m");
else {
if (ioctl(control, LOOP_CTL_REMOVE, d->nr) < 0)
log_debug_errno(errno, "Failed to remove loop device: %m");
}
}
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;
}
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