Created
October 26, 2021 10:00
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#ifndef _GNU_SOURCE | |
#define _GNU_SOURCE | |
#endif | |
#include <fcntl.h> | |
#include <limits.h> | |
#include <linux/loop.h> | |
#include <stdio.h> | |
#include <string.h> | |
#include <sys/ioctl.h> | |
#include <sys/types.h> | |
#include <unistd.h> | |
void fd_cleanup(int *fd) { | |
if (fd != NULL && *fd >= 0) { | |
close(*fd); | |
*fd = -1; | |
} | |
} | |
#define CLEANUP(__f) __attribute__((__cleanup__(__f))) | |
int main(int argc, char *argv[]) { | |
const char *fname = NULL; | |
if (argc < 2) { | |
fprintf(stderr, "usage: %s <snap-file-name>\n", argv[0]); | |
return 1; | |
} | |
fname = argv[1]; | |
int f CLEANUP(fd_cleanup) = open(fname, O_RDONLY | O_CLOEXEC | O_DIRECT); | |
if (f < 0) { | |
perror("open snap failed"); | |
return 1; | |
} | |
int lc CLEANUP(fd_cleanup) = open("/dev/loop-control", O_RDWR | O_CLOEXEC); | |
if (lc < 0) { | |
perror("opening loop-control failed"); | |
return 1; | |
} | |
int loop_free = ioctl(lc, LOOP_CTL_GET_FREE); | |
if (loop_free < 0) { | |
perror("get free failed"); | |
return 1; | |
} | |
fprintf(stderr, "got device %d\n", loop_free); | |
char loop_dev_path[PATH_MAX] = {0}; | |
snprintf(loop_dev_path, sizeof(loop_dev_path), "/dev/loop%d", loop_free); | |
int ldev CLEANUP(fd_cleanup) = open(loop_dev_path, O_RDWR | O_CLOEXEC); | |
if (ldev < 0) { | |
perror("cannot open loop device"); | |
return 1; | |
} | |
struct loop_config config = { | |
.fd = f, | |
.block_size = 0, | |
.info = | |
{ | |
.lo_flags = LO_FLAGS_DIRECT_IO | LO_FLAGS_READ_ONLY, | |
}, | |
}; | |
strncpy(config.info.lo_file_name, fname, sizeof(config.info.lo_file_name)); | |
if (ioctl(ldev, LOOP_CONFIGURE, &config)) { | |
perror("loop configure failed"); | |
return 1; | |
} | |
return 0; | |
} |
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