nbd: support large NBD requests

The Linux nbd driver recently increased the maximum supported request
size up to 32 MB:

  commit 078be02b80359a541928c899c2631f39628f56df
  Author: Michal Belczyk <belczyk@bsd.krakow.pl>
  Date:   Tue Apr 30 15:28:28 2013 -0700

      nbd: increase default and max request sizes

      Raise the default max request size for nbd to 128KB (from 127KB) to get it
      4KB aligned.  This patch also allows the max request size to be increased
      (via /sys/block/nbd<x>/queue/max_sectors_kb) to 32MB.

QEMU's 1 MB buffers are too small to handle these requests.

This patch allocates data buffers dynamically and allows up to 32 MB per
request.

Reported-by: Nick Thomas <nick@bytemark.co.uk>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

1 files changed, 11 insertions, 6 deletions

diff --git a/nbd.c b/nbd.c
index 761f4ec826..2606403a41 100644
--- a/nbd.c
+++ b/nbd.c
@@ -844,13 +844,11 @@ void nbd_client_close(NBDClient *client)
 static NBDRequest *nbd_request_get(NBDClient *client)
 {
     NBDRequest *req;
-    NBDExport *exp = client->exp;
 
     assert(client->nb_requests <= MAX_NBD_REQUESTS - 1);
     client->nb_requests++;
 
     req = g_slice_new0(NBDRequest);
-    req->data = qemu_blockalign(exp->bs, NBD_BUFFER_SIZE);
     nbd_client_get(client);
     req->client = client;
     return req;
@@ -860,7 +858,9 @@ static void nbd_request_put(NBDRequest *req)
 {
     NBDClient *client = req->client;
 
-    qemu_vfree(req->data);
+    if (req->data) {
+        qemu_vfree(req->data);
+    }
     g_slice_free(NBDRequest, req);
 
     if (client->nb_requests-- == MAX_NBD_REQUESTS) {
@@ -1007,6 +1007,7 @@ static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *reque
 {
     NBDClient *client = req->client;
     int csock = client->sock;
+    uint32_t command;
     ssize_t rc;
 
     client->recv_coroutine = qemu_coroutine_self();
@@ -1018,9 +1019,9 @@ static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *reque
         goto out;
     }
 
-    if (request->len > NBD_BUFFER_SIZE) {
+    if (request->len > NBD_MAX_BUFFER_SIZE) {
         LOG("len (%u) is larger than max len (%u)",
-            request->len, NBD_BUFFER_SIZE);
+            request->len, NBD_MAX_BUFFER_SIZE);
         rc = -EINVAL;
         goto out;
     }
@@ -1034,7 +1035,11 @@ static ssize_t nbd_co_receive_request(NBDRequest *req, struct nbd_request *reque
 
     TRACE("Decoding type");
 
-    if ((request->type & NBD_CMD_MASK_COMMAND) == NBD_CMD_WRITE) {
+    command = request->type & NBD_CMD_MASK_COMMAND;
+    if (command == NBD_CMD_READ || command == NBD_CMD_WRITE) {
+        req->data = qemu_blockalign(client->exp->bs, request->len);
+    }
+    if (command == NBD_CMD_WRITE) {
         TRACE("Reading %u byte(s)", request->len);
 
         if (qemu_co_recv(csock, req->data, request->len) != request->len) {