This helps to avoid extra io, allocations and memory copying. We assume here that CMD_CACHE is always used with copy-on-read, as otherwise it's a noop.
Signed-off-by: Vladimir Sementsov-Ogievskiy <vsement...@virtuozzo.com> --- nbd/server.c | 43 +++++++++++++++++++++++++++++++++++-------- 1 file changed, 35 insertions(+), 8 deletions(-) diff --git a/nbd/server.c b/nbd/server.c index aeca3893fe..6048257872 100644 --- a/nbd/server.c +++ b/nbd/server.c @@ -2101,12 +2101,15 @@ static int nbd_co_receive_request(NBDRequestData *req, NBDRequest *request, return -EINVAL; } - req->data = blk_try_blockalign(client->exp->blk, request->len); - if (req->data == NULL) { - error_setg(errp, "No memory"); - return -ENOMEM; + if (request->type != NBD_CMD_CACHE) { + req->data = blk_try_blockalign(client->exp->blk, request->len); + if (req->data == NULL) { + error_setg(errp, "No memory"); + return -ENOMEM; + } } } + if (request->type == NBD_CMD_WRITE) { if (nbd_read(client->ioc, req->data, request->len, "CMD_WRITE data", errp) < 0) @@ -2191,7 +2194,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request, int ret; NBDExport *exp = client->exp; - assert(request->type == NBD_CMD_READ || request->type == NBD_CMD_CACHE); + assert(request->type == NBD_CMD_READ); /* XXX: NBD Protocol only documents use of FUA with WRITE */ if (request->flags & NBD_CMD_FLAG_FUA) { @@ -2203,7 +2206,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request, } if (client->structured_reply && !(request->flags & NBD_CMD_FLAG_DF) && - request->len && request->type != NBD_CMD_CACHE) + request->len) { return nbd_co_send_sparse_read(client, request->handle, request->from, data, request->len, errp); @@ -2211,7 +2214,7 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request, ret = blk_pread(exp->blk, request->from + exp->dev_offset, data, request->len); - if (ret < 0 || request->type == NBD_CMD_CACHE) { + if (ret < 0) { return nbd_send_generic_reply(client, request->handle, ret, "reading from file failed", errp); } @@ -2230,6 +2233,28 @@ static coroutine_fn int nbd_do_cmd_read(NBDClient *client, NBDRequest *request, } } +/* + * nbd_do_cmd_cache + * + * Handle NBD_CMD_CACHE request. + * Return -errno if sending fails. Other errors are reported directly to the + * client as an error reply. + */ +static coroutine_fn int nbd_do_cmd_cache(NBDClient *client, NBDRequest *request, + Error **errp) +{ + int ret; + NBDExport *exp = client->exp; + + assert(request->type == NBD_CMD_CACHE); + + ret = blk_co_preadv(exp->blk, request->from + exp->dev_offset, request->len, + NULL, BDRV_REQ_COPY_ON_READ | BDRV_REQ_PREFETCH); + + return nbd_send_generic_reply(client, request->handle, ret, + "caching data failed", errp); +} + /* Handle NBD request. * Return -errno if sending fails. Other errors are reported directly to the * client as an error reply. */ @@ -2243,8 +2268,10 @@ static coroutine_fn int nbd_handle_request(NBDClient *client, char *msg; switch (request->type) { - case NBD_CMD_READ: case NBD_CMD_CACHE: + return nbd_do_cmd_cache(client, request, errp); + + case NBD_CMD_READ: return nbd_do_cmd_read(client, request, data, errp); case NBD_CMD_WRITE: -- 2.18.0