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

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; > --- > block/copy-on-read.c | 13 +++++++++---- > block/io.c | 3 ++- > 2 files changed, 11 insertions(+), 5 deletions(-) > > diff --git a/block/copy-on-read.c b/block/copy-on-read.c > index b136895..278a11a 100644 > --- a/block/copy-on-read.c > +++ b/block/copy-on-read.c > @@ -148,10 +148,15 @@ static int coroutine_fn cor_co_preadv_part(BlockDriverState *bs, > } > } > > - ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset, > - local_flags); > - if (ret < 0) { > - return ret; > + if (!!(flags & BDRV_REQ_PREFETCH) & How about dropping the double negation and using a logical && instead of the binary &? > + !(local_flags & BDRV_REQ_COPY_ON_READ)) { > + /* Skip non-guest reads if no copy needed */ > + } else { Hm. I would have just written the negated form (!(flags & BDRV_REQ_PREFETCH) || (local_flags & BDRV_REQ_COPY_ON_READ)) and put the “skip” comment above that condition. (Since local_flags is initialized to flags, it can be written as a single comparison, but that’s a matter of taste and I’m not going to recommend either over the other: ((local_flags & (BDRV_REQ_PREFETCH | BDRV_REQ_COPY_ON_READ)) != BDRV_REQ_PREFETCH) ) > + ret = bdrv_co_preadv_part(bs->file, offset, n, qiov, qiov_offset, > + local_flags); > + if (ret < 0) { > + return ret; > + } > } > > offset += n; > 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);

Ah, OK. I see. I expected this to be a separate patch. I still wonder why it isn’t.