[libvirt] [PATCH 2/4] logical: Create helper virStorageBackendLogicalParseVolDevice

[John Ferlan]

On 01/26/2016 09:46 AM, Pavel Hrdina wrote:
> On Fri, Jan 22, 2016 at 05:21:04PM -0500, John Ferlan wrote:
>> Create a helper routine in order to parse the 'device' string contained
>> within the generated 'lvs' output string.
>>
>> A future patch would then be able to avoid the code more cleanly
>>
>> Signed-off-by: John Ferlan <jferlan at redhat.com>
>> ---
>>  src/storage/storage_backend_logical.c | 186 +++++++++++++++++++---------------
>>  1 file changed, 104 insertions(+), 82 deletions(-)
>>
>> diff --git a/src/storage/storage_backend_logical.c b/src/storage/storage_backend_logical.c
>> index 76ea00a..bf67faf 100644
>> --- a/src/storage/storage_backend_logical.c
>> +++ b/src/storage/storage_backend_logical.c
>> @@ -72,21 +72,115 @@ struct virStorageBackendLogicalPoolVolData {
>>  };
>>  
>>  static int
>> -virStorageBackendLogicalMakeVol(char **const groups,
>> -                                void *opaque)
>> +virStorageBackendLogicalParseVolDevice(virStorageVolDefPtr vol,
>> +                                       char **const groups,
>> +                                       int nextents,
>> +                                       unsigned long long size,
>> +                                       unsigned long long length)
>>  {
> 
> You've called the new helper *ParseVolDevice, but it actually does more than
> that.  I would rather see it like ParseExtents and also move all the extents
> related code into this function (parsing length and size)

OK - my goal was to just parse the devices/extents element so that the
next patch could use the 'nextents' to decide whether to call it...  The
'nextents' is just the count... Having more than 1 is seen in a
'striped' and 'mirror' lv. A 'thin' lv has 0... A 'thin-pool' and
'linear' each has 1... Names are found in the 'segtype' field, but it's
otherwise useless. Perhaps originally the thought when adding a parse of
that field was that the 'stripes' value only was valid for stripes and
mirrors, but it seems it's set depending on the count of devices - so it
seems safe to use it for the extents parsing.

FWIW: The "extents" look like:

/dev/hda2(0)     <--- linear

or

/dev/sdc1(10240),/dev/sdd1(0)     <--- striped

or

thinpool_lv_test_thin_tdata(0)    <--- thin-pool


The "extents" gets further 'regcomp' and 'regexec''d to grab that "(#)"
which is part of the black magic that I cannot explain ;-)

> 
> [...]
> 
>> +    /* vars[0] is skipped */
>> +    for (i = 0; i < nextents; i++) {
>> +        size_t j;
>> +        int len;
>> +        char *offset_str = NULL;
>> +
>> +        j = (i * 2) + 1;
>> +        len = vars[j].rm_eo - vars[j].rm_so;
>> +        p[vars[j].rm_eo] = '\0';
>> +
>> +        if (VIR_STRNDUP(vol->source.extents[vol->source.nextent].path,
>> +                        p + vars[j].rm_so, len) < 0)
>> +            goto cleanup;
>> +
>> +        len = vars[j + 1].rm_eo - vars[j + 1].rm_so;
>> +        if (VIR_STRNDUP(offset_str, p + vars[j + 1].rm_so, len) < 0)
>> +            goto cleanup;
>> +
>> +        if (virStrToLong_ull(offset_str, NULL, 10, &offset) < 0) {
>> +            virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
>> +                           _("malformed volume extent offset value"));
>> +            VIR_FREE(offset_str);
>> +            goto cleanup;
>> +        }
>> +
>> +        VIR_FREE(offset_str);
>> +
>> +        vol->source.extents[vol->source.nextent].start = offset * size;
>> +        vol->source.extents[vol->source.nextent].end = (offset * size) + length;
>> +        vol->source.nextent++;
> 
> This would be much nicer to be done using VIR_APPEND_ELEMENT().  I know that
> this commit is just a code movement so this should be done in separate commit.
> 

Yes I pretty much blindly moved "just" the devices parsing code, but I
will note that we're not appending here - it's filling it in. Back in
the caller "vol->source.extents" is allocated using
"vol->source.nextents + nextents".  A "new" vol would have
"source.nextents == 0".  All this loop does is fill in each
source.extents and bump the source.nextents.

In any case, I will move the allocation of source.extents, fetch of
length and size into the helper (and rename it).

John