Re: [Libguestfs] [PATCH RFC] blkid: start using libblkid directly instead

On Tue, Feb 14, 2012 at 08:56:12AM +0000, Richard W.M. Jones wrote: > On Tue, Feb 14, 2012 at 03:30:26PM +0800, Wanlong Gao wrote: > It's one of those things that might be an improvement, but it would > have to be distinctly better than the existing approach of calling out > to the 'blkid' binary. > > Is the libblkid library interface stable? Is it meant to be used by > programs other than the blkid binary? Yes, for example the latest udevd is linked with libblkid. >> +#include <blkid/blkid.h> #include <blkid.h> if you want to use pkg-config >> static char * >> get_blkid_tag (const char *device, const char *tag) >> { >> - char *out, *err; >> - int r; >> + int fd, rc; >> + const char *data = NULL; >> + blkid_probe blkprobe; >> >> - r = commandr (&out, &err, >> - "blkid", >> - /* Adding -c option kills all caching, even on RHEL 5. */ >> - "-c", "/dev/null", >> - "-o", "value", "-s", tag, device, NULL); >> - if (r != 0 && r != 2) { >> - if (r >= 0) >> - reply_with_error ("%s: %s (blkid returned %d)", device, err, r); >> - else >> - reply_with_error ("%s: %s", device, err); >> - free (out); >> - free (err); >> + if (!device || !tag) >> return NULL; >> - } >> >> - free (err); >> + fd = open (device, O_RDONLY); >> + if (fd < 0) >> + return NULL; >> >> - if (r == 2) { /* means UUID etc not found */ >> - free (out); >> - out = strdup (""); >> - if (out == NULL) >> - reply_with_perror ("strdup"); >> - return out; >> - } >> + blkprobe = blkid_new_probe (); >> + if (!blkprobe) >> + goto done; >> + if (blkid_probe_set_device (blkprobe, fd, 0, 0)) >> + goto done; >> + >> + blkid_probe_enable_superblocks(blkprobe, 1); You can also optionally enable blkid_probe_enable_partitions(pr, 1); to check for collisions between raids and partition tables (for example RAID1 could be partitioned -- then PT could be at the begin of the device and raid superblock at the end of the device, etc.) >> + blkid_probe_set_superblocks_flags (blkprobe, BLKID_SUBLKS_LABEL | >> + BLKID_SUBLKS_UUID | BLKID_SUBLKS_TYPE); >> >> - /* Trim trailing \n if present. */ >> - size_t len = strlen (out); >> - if (len > 0 && out[len-1] == '\n') >> - out[len-1] = '\0'; >> + rc = blkid_do_safeprobe (blkprobe); >> + if (!rc) >> + blkid_probe_lookup_value (blkprobe, tag, &data, NULL); >> >> - return out; /* caller frees */ >> +done: >> + close (fd); >> + if (blkprobe) >> + blkid_free_probe (blkprobe); >> + return data ? strdup ((char *) data) : NULL; after blkid_free_probe() the "data" are deallocated, must be: done: close (fd); if (data) data = strdup ((char *) data); blkid_free_probe (blkprobe); return data; Note that if-before-free is unnecessary for blkid_free_probe. Karel