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

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?

> +#include <blkid/blkid.h>

> 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);

> + 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;