Commit 7fa5c565 authored by Vladimir Sementsov-Ogievskiy's avatar Vladimir Sementsov-Ogievskiy Committed by Eric Blake
Browse files

nbd: improve CMD_CACHE: use BDRV_REQ_PREFETCH 



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: default avatarVladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20190725100550.33801-4-vsementsov@virtuozzo.com>
Reviewed-by: default avatarEric Blake <eblake@redhat.com>
Reviewed-by: default avatarStefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: default avatarEric Blake <eblake@redhat.com>
parent 99136607

nbd/server.c

+35 −8
Original line number Diff line number Diff line
@@ -2104,12 +2104,15 @@ static int nbd_co_receive_request(NBDRequestData *req, NBDRequest *request, 
            return -EINVAL;

        }



        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)
@@ -2194,7 +2197,7 @@ 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) {
@@ -2206,7 +2209,7 @@ 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);
@@ -2214,7 +2217,7 @@ 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);

    }
@@ -2233,6 +2236,28 @@ 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. */
@@ -2246,8 +2271,10 @@ 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: