Libguestfs - Jun 2023 - [PATCH v4 23/24] nbd/server: Prepare for per-request filtering of BLOCK_STATUS

The next commit will add support for the optional extension
NBD_CMD_FLAG_PAYLOAD during NBD_CMD_BLOCK_STATUS, where the client can
request that the server only return a subset of negotiated contexts,
rather than all contexts.  To make that task easier, this patch
populates the list of contexts to return on a per-command basis (for
now, identical to the full set of negotiated contexts).

Signed-off-by: Eric Blake <eblake at redhat.com>
---

v4: split out NBDMetaContexts refactoring to its own patch, track
NBDRequests.contexts as a pointer rather than inline
---
 include/block/nbd.h |  1 +
 nbd/server.c        | 22 +++++++++++++++++-----
 2 files changed, 18 insertions(+), 5 deletions(-)

diff --git a/include/block/nbd.h b/include/block/nbd.h
index f240707f646..47850be5a66 100644
--- a/include/block/nbd.h
+++ b/include/block/nbd.h
@@ -76,6 +76,7 @@ typedef struct NBDRequest {
     uint16_t flags; /* NBD_CMD_FLAG_* */
     uint16_t type;  /* NBD_CMD_* */
     NBDMode mode;   /* Determines which network representation to use */
+    NBDMetaContexts *contexts; /* Used by NBD_CMD_BLOCK_STATUS */
 } NBDRequest;

 typedef struct NBDSimpleReply {
diff --git a/nbd/server.c b/nbd/server.c
index 42a4300c95e..308846fe46b 100644
--- a/nbd/server.c
+++ b/nbd/server.c
@@ -2491,6 +2491,8 @@ static int coroutine_fn
nbd_co_receive_request(NBDRequestData *req, NBDRequest *
             error_setg(errp, "No memory");
             return -ENOMEM;
         }
+    } else if (request->type == NBD_CMD_BLOCK_STATUS) {
+        request->contexts = &client->contexts;
     }

     if (payload_len) {
@@ -2716,11 +2718,11 @@ static coroutine_fn int nbd_handle_request(NBDClient
*client,
         }
         assert(client->mode >= NBD_MODE_EXTENDED ||
                request->len <= UINT32_MAX);
-        if (client->contexts.count) {
+        if (request->contexts->count) {
             bool dont_fragment = request->flags & NBD_CMD_FLAG_REQ_ONE;
-            int contexts_remaining = client->contexts.count;
+            int contexts_remaining = request->contexts->count;

-            if (client->contexts.base_allocation) {
+            if (request->contexts->base_allocation) {
                 ret = nbd_co_send_block_status(client, request,
                                                exp->common.blk,
                                                request->from,
@@ -2733,7 +2735,7 @@ static coroutine_fn int nbd_handle_request(NBDClient
*client,
                 }
             }

-            if (client->contexts.allocation_depth) {
+            if (request->contexts->allocation_depth) {
                 ret = nbd_co_send_block_status(client, request,
                                                exp->common.blk,
                                                request->from,
request->len,
@@ -2746,8 +2748,9 @@ static coroutine_fn int nbd_handle_request(NBDClient
*client,
                 }
             }

+            assert(request->contexts->exp == client->exp);
             for (i = 0; i < client->exp->nr_export_bitmaps; i++) {
-                if (!client->contexts.bitmaps[i]) {
+                if (!request->contexts->bitmaps[i]) {
                     continue;
                 }
                 ret = nbd_co_send_bitmap(client, request,
@@ -2763,6 +2766,10 @@ static coroutine_fn int nbd_handle_request(NBDClient
*client,
             assert(!contexts_remaining);

             return 0;
+        } else if (client->contexts.count) {
+            return nbd_send_generic_reply(client, request, -EINVAL,
+                                          "CMD_BLOCK_STATUS payload not
valid",
+                                          errp);
         } else {
             return nbd_send_generic_reply(client, request, -EINVAL,
                                           "CMD_BLOCK_STATUS not
negotiated",
@@ -2841,6 +2848,11 @@ static coroutine_fn void nbd_trip(void *opaque)
     } else {
         ret = nbd_handle_request(client, &request, req->data,
&local_err);
     }
+    if (request.type == NBD_CMD_BLOCK_STATUS &&
+        request.contexts != &client->contexts) {
+        g_free(request.contexts->bitmaps);
+        g_free(request.contexts);
+    }
     if (ret < 0) {
         error_prepend(&local_err, "Failed to send reply: ");
         goto disconnect;
-- 
2.40.1

On Thu, Jun 08, 2023 at 08:56:52AM -0500, Eric Blake
wrote:
> The next commit will add support for the optional extension
> NBD_CMD_FLAG_PAYLOAD during NBD_CMD_BLOCK_STATUS, where the client can
> request that the server only return a subset of negotiated contexts,
> rather than all contexts.  To make that task easier, this patch
> populates the list of contexts to return on a per-command basis (for
> now, identical to the full set of negotiated contexts).
> 
> Signed-off-by: Eric Blake <eblake at redhat.com>
> ---
> 
> +++ b/nbd/server.c
> @@ -2491,6 +2491,8 @@ static int coroutine_fn
nbd_co_receive_request(NBDRequestData *req, NBDRequest *
>              error_setg(errp, "No memory");
>              return -ENOMEM;
>          }
> +    } else if (request->type == NBD_CMD_BLOCK_STATUS) {
> +        request->contexts = &client->contexts;
>      }
THere are paths where request->contexts is left NULL but request->type
was set...
> @@ -2841,6 +2848,11 @@ static coroutine_fn void nbd_trip(void *opaque)
>      } else {
>          ret = nbd_handle_request(client, &request, req->data,
&local_err);
>      }
> +    if (request.type == NBD_CMD_BLOCK_STATUS &&
> +        request.contexts != &client->contexts) {
> +        g_free(request.contexts->bitmaps);
> +        g_free(request.contexts);
> +    }
so I think this also needs to be tweaked to check that
request.contexts is non-NULL before dereferencing to free bitmaps.

-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3266
Virtualization:  qemu.org | libvirt.org