Re: [Qemu-devel] [PATCH 1/6] block: Support byte-based aio callbacks

[Eric Blake]

On 04/24/2018 10:40 AM, Kevin Wolf wrote:
> Am 15.02.2018 um 20:28 hat Eric Blake geschrieben:
>> We are gradually moving away from sector-based interfaces, towards
>> byte-based.  Add new sector-based aio callbacks for read and write,
>> to match the fact that bdrv_aio_pdiscard is already byte-based.
>>
>> Ideally, drivers should be converted to use coroutine callbacks
>> rather than aio; but that is not quite as trivial (if we do that
>> conversion, the null-aio driver will disappear), so for the
>> short term, converting the signature but keeping things with aio
>> is easier.  Once all drivers are converted, the sector-based aio
>> callbacks will be removed.
>>
>> Signed-off-by: Eric Blake <address@hidden>
>> ---
>>  include/block/block_int.h |  6 ++++++
>>  block/io.c                | 37 +++++++++++++++++++++++++++----------
>>  2 files changed, 33 insertions(+), 10 deletions(-)
>>

>> +++ b/block/io.c
>> @@ -934,9 +934,11 @@ static int coroutine_fn 
>> bdrv_driver_preadv(BlockDriverState *bs,
>>      sector_num = offset >> BDRV_SECTOR_BITS;
>>      nb_sectors = bytes >> BDRV_SECTOR_BITS;
>>
>> -    assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
>> -    assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
>> -    assert((bytes >> BDRV_SECTOR_BITS) <= BDRV_REQUEST_MAX_SECTORS);
>> +    if (!drv->bdrv_aio_preadv) {
>> +        assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
>> +        assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
>> +        assert((bytes >> BDRV_SECTOR_BITS) <= BDRV_REQUEST_MAX_SECTORS);
>> +    }
> 
> Hm, this is kind of ugly. Previously, we handled everything byte-aligned
> in the first section, now we mix both in the second section.
> 
> I can see that you do this so you don't have to duplicate the acb and
> coroutine yielding code below, but can we move things into the right
> place in the final patch at least? That is, calculate sector_num and
> nb_sectors only if all the byte-based interfaces weren't available.

Yeah, that's easy enough to squash into patch 6:

diff --git i/block/io.c w/block/io.c
index ba767612931..49fabe8eeb1 100644
--- i/block/io.c
+++ w/block/io.c
@@ -924,16 +924,13 @@ static int coroutine_fn
bdrv_driver_preadv(BlockDriverState *bs,
         return drv->bdrv_co_preadv(bs, offset, bytes, qiov, flags);
     }

-    sector_num = offset >> BDRV_SECTOR_BITS;
-    nb_sectors = bytes >> BDRV_SECTOR_BITS;
-
-    if (!drv->bdrv_aio_preadv) {
-        assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
-        assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
-        assert((bytes >> BDRV_SECTOR_BITS) <= BDRV_REQUEST_MAX_SECTORS);
-    }
-
     if (drv->bdrv_co_readv) {
+        sector_num = offset >> BDRV_SECTOR_BITS;
+        nb_sectors = bytes >> BDRV_SECTOR_BITS;
+
+        assert((offset & (BDRV_SECTOR_SIZE - 1)) == 0);
+        assert((bytes & (BDRV_SECTOR_SIZE - 1)) == 0);
+        assert((bytes >> BDRV_SECTOR_BITS) <= BDRV_REQUEST_MAX_SECTORS);
         return drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
     } else {
         BlockAIOCB *acb;

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org

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