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

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