Re: [Qemu-devel] [PATCH v3 2/3] raw-posix: raw_co_get_block_status() return value

[Max Reitz <mreitz@redhat.com>]

On 2014-10-22 at 19:00, Eric Blake wrote:
> On 10/22/2014 09:57 AM, Max Reitz wrote:
>> Instead of generating the full return value thrice in try_fiemap(),
>> try_seek_hole() and as a fall-back in raw_co_get_block_status() itself,
>> generate the value only in raw_co_get_block_status().
>>
>> While at it, also remove the pnum parameter from try_fiemap() and
>> try_seek_hole().
>>
>> Suggested-by: Kevin Wolf <kwolf@redhat.com>
>> Signed-off-by: Max Reitz <mreitz@redhat.com>
>> ---
>>   block/raw-posix.c | 28 ++++++++++++++--------------
>>   1 file changed, 14 insertions(+), 14 deletions(-)
> Reviewed-by: Eric Blake <eblake@redhat.com>
>
>> -    ret = try_seek_hole(bs, start, &data, &hole, pnum);
>> +    ret = try_seek_hole(bs, start, &data, &hole);
>>       if (ret < 0) {
>> -        ret = try_fiemap(bs, start, &data, &hole, nb_sectors, pnum);
>> +        ret = try_fiemap(bs, start, &data, &hole, nb_sectors);
>>           if (ret < 0) {
>>               /* Assume everything is allocated. */
>>               data = 0;
>>               hole = start + nb_sectors * BDRV_SECTOR_SIZE;
>> -            ret = BDRV_BLOCK_DATA | BDRV_BLOCK_OFFSET_VALID | start;
>> +            ret = 0;
>>           }
>>       }
>>   
>> +    assert(ret >= 0);
> I'm not sure the assertion adds much (the lines above are fairly easy to
> reason about ret always being set), but it does protect against later
> code addition, so I'm not opposed to leaving it.

I just liked it there to make clear that the previous code always goes 
into a fallback, so while some parts of it may throw errors, after 
everything is done, we're fine. The compiler will hopefully optimize it 
out anyway.

Max