Commit 3299e5ec authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by Eric Blake
Browse files

block: implement BDRV_REQ_PREFETCH 



Do effective copy-on-read request when we don't need data actually. It
will be used for block-stream and NBD_CMD_CACHE.

Signed-off-by: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20190725100550.33801-2-vsementsov@virtuozzo.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
[eblake: comment grammar fix]
Signed-off-by: default avatarEric Blake <eblake@redhat.com>
parent aec21d31

block/io.c

+12 −6
Original line number Diff line number Diff line
@@ -1167,7 +1167,8 @@ bdrv_driver_pwritev_compressed(BlockDriverState *bs, uint64_t offset, 
}



static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child,

        int64_t offset, unsigned int bytes, QEMUIOVector *qiov)

        int64_t offset, unsigned int bytes, QEMUIOVector *qiov,

        int flags)

{

    BlockDriverState *bs = child->bs;
@@ -1278,9 +1279,11 @@ static int coroutine_fn bdrv_co_do_copy_on_readv(BdrvChild *child, 
                goto err;

            }



            if (!(flags & BDRV_REQ_PREFETCH)) {

                qemu_iovec_from_buf(qiov, progress, bounce_buffer + skip_bytes,

                                    pnum - skip_bytes);

        } else {

            }

        } else if (!(flags & BDRV_REQ_PREFETCH)) {

            /* Read directly into the destination */

            qemu_iovec_init(&local_qiov, qiov->niov);

            qemu_iovec_concat(&local_qiov, qiov, progress, pnum - skip_bytes);
@@ -1331,7 +1334,8 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child, 
     * potential fallback support, if we ever implement any read flags

     * to pass through to drivers.  For now, there aren't any

     * passthrough flags.  */

    assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ)));

    assert(!(flags & ~(BDRV_REQ_NO_SERIALISING | BDRV_REQ_COPY_ON_READ |

                       BDRV_REQ_PREFETCH)));



    /* Handle Copy on Read and associated serialisation */

    if (flags & BDRV_REQ_COPY_ON_READ) {
@@ -1359,7 +1363,9 @@ static int coroutine_fn bdrv_aligned_preadv(BdrvChild *child, 
        }



        if (!ret || pnum != bytes) {

            ret = bdrv_co_do_copy_on_readv(child, offset, bytes, qiov);

            ret = bdrv_co_do_copy_on_readv(child, offset, bytes, qiov, flags);

            goto out;

        } else if (flags & BDRV_REQ_PREFETCH) {

            goto out;

        }

    }

include/block/block.h

+7 −1
Original line number Diff line number Diff line
@@ -88,8 +88,14 @@ typedef enum { 
     * fallback. */

    BDRV_REQ_NO_FALLBACK        = 0x100,



    /*

     * BDRV_REQ_PREFETCH may be used only together with BDRV_REQ_COPY_ON_READ

     * on read request and means that caller doesn't really need data to be

     * written to qiov parameter which may be NULL.

     */

    BDRV_REQ_PREFETCH  = 0x200,

    /* Mask of valid flags */

    BDRV_REQ_MASK               = 0x1ff,

    BDRV_REQ_MASK               = 0x3ff,

} BdrvRequestFlags;



typedef struct BlockSizes {