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loop-util: allow creating loopback block devices with offset/length

This commit is contained in:
Lennart Poettering 2019-07-04 17:57:29 +02:00
parent 9dabc4fda5
commit ed9eeb7b0b
2 changed files with 41 additions and 25 deletions
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60
src/shared/loop-util.c
View File

@ -10,15 +10,18 @@
#include "loop-util.h"
#include "stat-util.h"
int loop_device_make(int fd, int open_flags, uint32_t loop_flags, LoopDevice **ret) {
const struct loop_info64 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) | ((loop_flags & O_ACCMODE) == O_RDONLY ? LO_FLAGS_READ_ONLY : 0) | LO_FLAGS_AUTOCLEAR,
};
int loop_device_make_full(
int fd,
int open_flags,
uint64_t offset,
uint64_t size,
uint32_t loop_flags,
LoopDevice **ret) {
_cleanup_close_ int control = -1, loop = -1;
_cleanup_free_ char *loopdev = NULL;
unsigned n_attempts = 0;
struct loop_info64 info;
struct stat st;
LoopDevice *d;
int nr, r;
@ -31,32 +34,34 @@ int loop_device_make(int fd, int open_flags, uint32_t loop_flags, LoopDevice **r
return -errno;
if (S_ISBLK(st.st_mode)) {
int copy;
if (offset == 0 && IN_SET(size, 0, UINT64_MAX)) {
int copy;
/* If this is already a block device, store a copy of the fd as it is */
/* 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;
copy = fcntl(fd, F_DUPFD_CLOEXEC, 3);
if (copy < 0)
return -errno;
d = new0(LoopDevice, 1);
if (!d)
return -ENOMEM;
d = new(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 */
};
*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;
*ret = d;
return d->fd;
}
} else {
r = stat_verify_regular(&st);
if (r < 0)
return r;
}
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;
@ -87,6 +92,13 @@ int loop_device_make(int fd, int open_flags, uint32_t loop_flags, LoopDevice **r
loop = safe_close(loop);
}
info = (struct loop_info64) {
/* 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) | ((loop_flags & O_ACCMODE) == O_RDONLY ? LO_FLAGS_READ_ONLY : 0) | LO_FLAGS_AUTOCLEAR,
.lo_offset = offset,
.lo_sizelimit = size == UINT64_MAX ? 0 : size,
};
if (ioctl(loop, LOOP_SET_STATUS64, &info) < 0)
return -errno;

6
src/shared/loop-util.h
View File

@ -14,7 +14,11 @@ struct LoopDevice {
bool relinquished;
};
int loop_device_make(int fd, int open_flags, uint32_t loop_flags, LoopDevice **ret);
int loop_device_make_full(int fd, int open_flags, uint64_t offset, uint64_t size, uint32_t loop_flags, LoopDevice **ret);
static inline int loop_device_make(int fd, int open_flags, uint32_t loop_flags, LoopDevice **ret) {
return loop_device_make_full(fd, open_flags, 0, 0, loop_flags, ret);
}
int loop_device_make_by_path(const char *path, int open_flags, uint32_t loop_flags, LoopDevice **ret);
int loop_device_open(const char *loop_path, int open_flags, LoopDevice **ret);