Re: [PATCH v11 09/13] copy-on-read: skip non-guest reads if no copy needed

On 21.10.2020 23:43, Andrey Shinkevich wrote: > On 14.10.2020 18:22, Vladimir Sementsov-Ogievskiy wrote: >> 14.10.2020 15:51, Max Reitz wrote: >>> On 12.10.20 19:43, Andrey Shinkevich wrote: >>>> If the flag BDRV_REQ_PREFETCH was set, pass it further to the >>>> COR-driver to skip unneeded reading. It can be taken into account for >>>> the COR-algorithms optimization. That check is being made during the >>>> block stream job by the moment. >>>> >>>> Signed-off-by: Andrey Shinkevich <andrey.shinkevich(a)virtuozzo.com&gt; >>>> --- [...] >>>> diff --git a/block/io.c b/block/io.c >>>> index 11df188..bff1808 100644 >>>> --- a/block/io.c >>>> +++ b/block/io.c >>>> @@ -1512,7 +1512,8 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child, >>>>       max_bytes = ROUND_UP(MAX(0, total_bytes - offset), align); >>>>       if (bytes <= max_bytes && bytes <= max_transfer) { >>>> -        ret = bdrv_driver_preadv(bs, offset, bytes, qiov, qiov_offset, 0); >>>> +        ret = bdrv_driver_preadv(bs, offset, bytes, qiov, qiov_offset, >>>> +                                 flags & bs->supported_read_flags); >> >> >> When BDRV_REQ_PREFETCH is passed, qiov may be (and generally should be) NULL. This means, that we can't just drop the flag when call the driver that doesn't support it. >> >> Actually, if driver doesn't support the PREFETCH flag we should do nothing. >> >> >>> >>> Ah, OK.  I see.  I expected this to be a separate patch.  I still wonder >>> why it isn’t. >>> >> >> >> Could it be part of patch 07? I mean introduce new field supported_read_flags and handle it in generic code in one patch, prior to implementing support for it in COR driver. >> >> > > We have to add the supported flags for the COR driver in the same patch. Or before handling the supported_read_flags at the generic layer (handling zero does not make a sence). Otherwise, the test #216 (where the COR-filter is applied) will not pass. > > Andrey I have found a workaround and am going to send all the related patches as a separate series.