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block: core copy-on-read logic
Signed-off-by: Stefan Hajnoczi <stefanha@linux.vnet.ibm.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
parent
d83947ac6d
commit
ab1859218a
72
block.c
72
block.c
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@ -1469,6 +1469,61 @@ int bdrv_pwrite_sync(BlockDriverState *bs, int64_t offset,
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return 0;
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}
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static int coroutine_fn bdrv_co_copy_on_readv(BlockDriverState *bs,
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int64_t sector_num, int nb_sectors, QEMUIOVector *qiov)
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{
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/* Perform I/O through a temporary buffer so that users who scribble over
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* their read buffer while the operation is in progress do not end up
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* modifying the image file. This is critical for zero-copy guest I/O
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* where anything might happen inside guest memory.
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*/
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void *bounce_buffer;
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struct iovec iov;
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QEMUIOVector bounce_qiov;
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int64_t cluster_sector_num;
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int cluster_nb_sectors;
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size_t skip_bytes;
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int ret;
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/* Cover entire cluster so no additional backing file I/O is required when
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* allocating cluster in the image file.
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*/
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round_to_clusters(bs, sector_num, nb_sectors,
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&cluster_sector_num, &cluster_nb_sectors);
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trace_bdrv_co_copy_on_readv(bs, sector_num, nb_sectors,
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cluster_sector_num, cluster_nb_sectors);
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iov.iov_len = cluster_nb_sectors * BDRV_SECTOR_SIZE;
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iov.iov_base = bounce_buffer = qemu_blockalign(bs, iov.iov_len);
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qemu_iovec_init_external(&bounce_qiov, &iov, 1);
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ret = bs->drv->bdrv_co_readv(bs, cluster_sector_num, cluster_nb_sectors,
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&bounce_qiov);
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if (ret < 0) {
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goto err;
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}
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ret = bs->drv->bdrv_co_writev(bs, cluster_sector_num, cluster_nb_sectors,
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&bounce_qiov);
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if (ret < 0) {
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/* It might be okay to ignore write errors for guest requests. If this
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* is a deliberate copy-on-read then we don't want to ignore the error.
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* Simply report it in all cases.
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*/
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goto err;
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}
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skip_bytes = (sector_num - cluster_sector_num) * BDRV_SECTOR_SIZE;
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qemu_iovec_from_buffer(qiov, bounce_buffer + skip_bytes,
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nb_sectors * BDRV_SECTOR_SIZE);
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err:
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qemu_vfree(bounce_buffer);
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return ret;
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}
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/*
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* Handle a read request in coroutine context
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*/
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@ -1496,7 +1551,24 @@ static int coroutine_fn bdrv_co_do_readv(BlockDriverState *bs,
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}
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tracked_request_begin(&req, bs, sector_num, nb_sectors, false);
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if (bs->copy_on_read) {
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int pnum;
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ret = bdrv_co_is_allocated(bs, sector_num, nb_sectors, &pnum);
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if (ret < 0) {
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goto out;
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}
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if (!ret || pnum != nb_sectors) {
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ret = bdrv_co_copy_on_readv(bs, sector_num, nb_sectors, qiov);
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goto out;
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}
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}
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ret = drv->bdrv_co_readv(bs, sector_num, nb_sectors, qiov);
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out:
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tracked_request_end(&req);
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return ret;
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}
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@ -69,6 +69,7 @@ bdrv_lock_medium(void *bs, bool locked) "bs %p locked %d"
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bdrv_co_readv(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
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bdrv_co_writev(void *bs, int64_t sector_num, int nb_sector) "bs %p sector_num %"PRId64" nb_sectors %d"
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bdrv_co_io_em(void *bs, int64_t sector_num, int nb_sectors, int is_write, void *acb) "bs %p sector_num %"PRId64" nb_sectors %d is_write %d acb %p"
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bdrv_co_copy_on_readv(void *bs, int64_t sector_num, int nb_sectors, int64_t cluster_sector_num, int cluster_nb_sectors) "bs %p sector_num %"PRId64" nb_sectors %d cluster_sector_num %"PRId64" cluster_nb_sectors %d"
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# hw/virtio-blk.c
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virtio_blk_req_complete(void *req, int status) "req %p status %d"
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