net/9p: add 'pooled_rbuffers' flag to struct p9_trans_module

This is a preparatory change for the subsequent patch: the RDMA
transport pulls the buffers for its 9p response messages from a
shared pool. [1] So this case has to be considered when choosing
an appropriate response message size in the subsequent patch.

Link: https://lore.kernel.org/all/Ys3jjg52EIyITPua@codewreck.org/ [1]
Link: https://lkml.kernel.org/r/79d24310226bc4eb037892b5c097ec4ad4819a03.1657920926.git.linux_oss@crudebyte.com
Signed-off-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

include/net/9p/transport.h

@@ -19,6 +19,10 @@
  * @list: used to maintain a list of currently available transports
  * @name: the human-readable name of the transport
  * @maxsize: transport provided maximum packet size
+ * @pooled_rbuffers: currently only set for RDMA transport which pulls the
+ *                   response buffers from a shared pool, and accordingly
+ *                   we're less flexible when choosing the response message
+ *                   size in this case
  * @def: set if this transport should be considered the default
  * @create: member function to create a new connection on this transport
  * @close: member function to discard a connection on this transport
@@ -38,6 +42,7 @@ struct p9_trans_module {
 	struct list_head list;
 	char *name;		/* name of transport */
 	int maxsize;		/* max message size of transport */
+	bool pooled_rbuffers;
 	int def;		/* this transport should be default */
 	struct module *owner;
 	int (*create)(struct p9_client *client,

net/9p/trans_fd.c

@@ -1083,6 +1083,7 @@ p9_fd_create(struct p9_client *client, const char *addr, char *args)
 static struct p9_trans_module p9_tcp_trans = {
 	.name = "tcp",
 	.maxsize = MAX_SOCK_BUF,
+	.pooled_rbuffers = false,
 	.def = 0,
 	.create = p9_fd_create_tcp,
 	.close = p9_fd_close,

net/9p/trans_rdma.c

@@ -739,6 +739,7 @@ error:
 static struct p9_trans_module p9_rdma_trans = {
 	.name = "rdma",
 	.maxsize = P9_RDMA_MAXSIZE,
+	.pooled_rbuffers = true,
 	.def = 0,
 	.owner = THIS_MODULE,
 	.create = rdma_create_trans,

net/9p/trans_virtio.c

@@ -802,6 +802,7 @@ static struct p9_trans_module p9_virtio_trans = {
 	 * page in zero copy.
 	 */
 	.maxsize = PAGE_SIZE * (VIRTQUEUE_NUM - 3),
+	.pooled_rbuffers = false,
 	.def = 1,
 	.owner = THIS_MODULE,
 };

net/9p/trans_xen.c

@@ -246,6 +246,7 @@ static irqreturn_t xen_9pfs_front_event_handler(int irq, void *r)
 static struct p9_trans_module p9_xen_trans = {
 	.name = "xen",
 	.maxsize = 1 << (XEN_9PFS_RING_ORDER + XEN_PAGE_SHIFT - 2),
+	.pooled_rbuffers = false,
 	.def = 1,
 	.create = p9_xen_create,
 	.close = p9_xen_close,