losetup: use /sys/dev/block/.../loop/backing_file
The basic loopdev attributes are available in sysfs since kernel 2.6.37. This patch uses the backing_file attribute from sysfs for very long filenames (the LOOP_GET_STATUS ioctl uses only 64 bytes for the filename). old version: # losetup -a /dev/loop0: [0804]:12865322 (/home/images/filesystems/this_is_really_really_long_directory_*) new version: # losetup -a /dev/loop0: [0804]:12865322 (/home/images/filesystems/this_is_really_really_long_directory_name/ext2.img) Signed-off-by: Karel Zak <kzak@redhat.com>
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20
TODO
20
TODO
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@ -4,6 +4,25 @@ login-utils:
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- clean up error codes
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- use err() and warn() macros rather than fprintf(stderr, ...)
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losetup
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-------
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- don't use ioclts if sysfs supports loop attributes (since 2.6.37,
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block/loopN/loop/* files)
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- don't open loopdev in looplist_next(), check if /sys/block/loopN/loop
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exists and returns ll.name rather than file descriptor
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- add sysfs based version of show_loop() and use it for non-root users
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sysfs
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-----
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- add lib/sysfs.c with functions that read block device attributes from /sys.
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For more details see devno.c from libblkid, lsblk.c and lomount.c.
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libblkid
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--------
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@ -17,6 +36,7 @@ libblkid
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- add support for dasd PT (used for example on s390)
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blkid(8)
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-------
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@ -82,6 +82,7 @@
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#define _PATH_PROC_MOUNTINFO "/proc/self/mountinfo"
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#define _PATH_SYS_BLOCK "/sys/block"
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#define _PATH_SYS_DEVBLOCK "/sys/dev/block"
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#ifndef _PATH_MOUNTED
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# ifdef MOUNTED /* deprecated */
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@ -80,6 +80,35 @@ struct looplist {
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#define LLFLG_SUBDIR (1 << 5) /* /dev/loop/N */
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#define LLFLG_DFLT (1 << 6) /* directly try to check default loops */
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/* TODO: move to lib/sysfs.c */
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static char *loopfile_from_sysfs(const char *device)
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{
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FILE *f;
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struct stat st;
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char buf[PATH_MAX], *res = NULL;
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if (stat(device, &st) || !S_ISBLK(st.st_mode))
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return NULL;
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snprintf(buf, sizeof(buf), _PATH_SYS_DEVBLOCK "/%d:%d/loop/backing_file",
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major(st.st_rdev), minor(st.st_rdev));
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f = fopen(buf, "r");
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if (!f)
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return NULL;
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if (fgets(buf, sizeof(buf), f)) {
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size_t sz = strlen(buf);
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if (sz) {
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buf[sz - 1] = '\0';
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res = xstrdup(buf);
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}
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}
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fclose(f);
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return res;
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}
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int
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is_loop_device (const char *device) {
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struct stat st;
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@ -379,13 +408,26 @@ show_loop_fd(int fd, char *device) {
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if (ioctl(fd, LOOP_GET_STATUS64, &loopinfo64) == 0) {
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char *lofile = NULL;
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loopinfo64.lo_file_name[LO_NAME_SIZE-2] = '*';
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loopinfo64.lo_file_name[LO_NAME_SIZE-1] = 0;
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loopinfo64.lo_crypt_name[LO_NAME_SIZE-1] = 0;
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/* ioctl has limited buffer for backing file name, since
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* kernel 2.6.37 the filename is available in sysfs too
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*/
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if (strlen((char *) loopinfo64.lo_file_name) == LO_NAME_SIZE - 1)
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lofile = loopfile_from_sysfs(device);
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if (!lofile)
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lofile = (char *) loopinfo64.lo_file_name;
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printf("%s: [%04" PRIx64 "]:%" PRIu64 " (%s)",
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device, loopinfo64.lo_device, loopinfo64.lo_inode,
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loopinfo64.lo_file_name);
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lofile);
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if (lofile != (char *) loopinfo64.lo_file_name)
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free(lofile);
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if (loopinfo64.lo_offset)
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printf(_(", offset %" PRIu64 ), loopinfo64.lo_offset);
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