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@virtuozzo.com> --- 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. Max
goto out; }