On 02/14/2012 06:53 PM, Karel Zak wrote:
> 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
>
I did like this.
Now get a problem like below:
The *vfs_type* calls this *get_blkid_tag* function.
I added a disk image to guestfish, this disk image
contains a partition "/dev/vda1" with "ext4" filesystem.
Then I ran *vfs_type /dev/vda1", I got the result,
but with "vfs_type /dev/vda", it hang.
It seems that the vfs_type can't get a type of /dev/vda,
it's right that the type of /dev/vda is unknown, but
why can't it go back with unknown result or NULL result?
Maybe there's something wrong with the code of *get_blkid_tag* ?
Can you give some advise? Karel? Rich?
Thanks
-Wanlong Gao
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