nbd: Implement NBD_CMD_WRITE_ZEROES on client
Upstream NBD protocol recently added the ability to efficiently write zeroes without having to send the zeroes over the wire, along with a flag to control whether the client wants a hole. The generic block code takes care of falling back to the obvious write of lots of zeroes if we return -ENOTSUP because the server does not have WRITE_ZEROES. Ideally, since NBD_CMD_WRITE_ZEROES does not involve any data over the wire, we want to support transactions that are much larger than the normal 32M limit imposed on NBD_CMD_WRITE. But the server may still have a limit smaller than UINT_MAX, so until experimental NBD protocol additions for advertising various command sizes is finalized (see [1], [2]), for now we just stick to the same limits as normal writes. [1] https://github.com/yoe/nbd/blob/extension-info/doc/proto.md [2] https://sourceforge.net/p/nbd/mailman/message/35081223/ Signed-off-by: Eric Blake <eblake@redhat.com> Message-Id: <1476469998-28592-17-git-send-email-eblake@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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@ -275,6 +275,41 @@ int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,
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return -reply.error;
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}
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int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
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int count, BdrvRequestFlags flags)
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{
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ssize_t ret;
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NBDClientSession *client = nbd_get_client_session(bs);
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NBDRequest request = {
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.type = NBD_CMD_WRITE_ZEROES,
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.from = offset,
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.len = count,
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};
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NBDReply reply;
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if (!(client->nbdflags & NBD_FLAG_SEND_WRITE_ZEROES)) {
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return -ENOTSUP;
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}
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if (flags & BDRV_REQ_FUA) {
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assert(client->nbdflags & NBD_FLAG_SEND_FUA);
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request.flags |= NBD_CMD_FLAG_FUA;
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}
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if (!(flags & BDRV_REQ_MAY_UNMAP)) {
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request.flags |= NBD_CMD_FLAG_NO_HOLE;
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}
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nbd_coroutine_start(client, &request);
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ret = nbd_co_send_request(bs, &request, NULL);
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if (ret < 0) {
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reply.error = -ret;
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} else {
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nbd_co_receive_reply(client, &request, &reply, NULL);
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}
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nbd_coroutine_end(client, &request);
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return -reply.error;
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}
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int nbd_client_co_flush(BlockDriverState *bs)
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{
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NBDClientSession *client = nbd_get_client_session(bs);
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@ -48,6 +48,8 @@ int nbd_client_co_pdiscard(BlockDriverState *bs, int64_t offset, int count);
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int nbd_client_co_flush(BlockDriverState *bs);
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int nbd_client_co_pwritev(BlockDriverState *bs, uint64_t offset,
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uint64_t bytes, QEMUIOVector *qiov, int flags);
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int nbd_client_co_pwrite_zeroes(BlockDriverState *bs, int64_t offset,
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int count, BdrvRequestFlags flags);
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int nbd_client_co_preadv(BlockDriverState *bs, uint64_t offset,
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uint64_t bytes, QEMUIOVector *qiov, int flags);
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@ -466,6 +466,7 @@ static int nbd_co_flush(BlockDriverState *bs)
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static void nbd_refresh_limits(BlockDriverState *bs, Error **errp)
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{
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bs->bl.max_pdiscard = NBD_MAX_BUFFER_SIZE;
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bs->bl.max_pwrite_zeroes = NBD_MAX_BUFFER_SIZE;
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bs->bl.max_transfer = NBD_MAX_BUFFER_SIZE;
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}
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@ -558,6 +559,7 @@ static BlockDriver bdrv_nbd = {
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.bdrv_file_open = nbd_open,
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.bdrv_co_preadv = nbd_client_co_preadv,
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.bdrv_co_pwritev = nbd_client_co_pwritev,
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.bdrv_co_pwrite_zeroes = nbd_client_co_pwrite_zeroes,
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.bdrv_close = nbd_close,
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.bdrv_co_flush_to_os = nbd_co_flush,
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.bdrv_co_pdiscard = nbd_client_co_pdiscard,
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@ -576,6 +578,7 @@ static BlockDriver bdrv_nbd_tcp = {
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.bdrv_file_open = nbd_open,
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.bdrv_co_preadv = nbd_client_co_preadv,
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.bdrv_co_pwritev = nbd_client_co_pwritev,
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.bdrv_co_pwrite_zeroes = nbd_client_co_pwrite_zeroes,
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.bdrv_close = nbd_close,
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.bdrv_co_flush_to_os = nbd_co_flush,
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.bdrv_co_pdiscard = nbd_client_co_pdiscard,
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@ -594,6 +597,7 @@ static BlockDriver bdrv_nbd_unix = {
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.bdrv_file_open = nbd_open,
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.bdrv_co_preadv = nbd_client_co_preadv,
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.bdrv_co_pwritev = nbd_client_co_pwritev,
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.bdrv_co_pwrite_zeroes = nbd_client_co_pwrite_zeroes,
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.bdrv_close = nbd_close,
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.bdrv_co_flush_to_os = nbd_co_flush,
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.bdrv_co_pdiscard = nbd_client_co_pdiscard,
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