net/9p: show error message if user 'msize' cannot be satisfied

If user supplied a large value with the 'msize' option, then
client would silently limit that 'msize' value to the maximum
value supported by transport. That's a bit confusing for users
of not having any indication why the preferred 'msize' value
could not be satisfied.

Link: https://lkml.kernel.org/r/783ba37c1566dd715b9a67d437efa3b77e3cd1a7.1640870037.git.linux_oss@crudebyte.com
Reported-by: Vivek Goyal <vgoyal@redhat.com>
Signed-off-by: Christian Schoenebeck <linux_oss@crudebyte.com>
Signed-off-by: Dominique Martinet <asmadeus@codewreck.org>

Author: cschoenebeck

net/9p/client.c

@@ -1038,8 +1038,13 @@ struct p9_client *p9_client_create(const char *dev_name, char *options)
 	if (err)
 		goto put_trans;
 
-	if (clnt->msize > clnt->trans_mod->maxsize)
+	if (clnt->msize > clnt->trans_mod->maxsize) {
 		clnt->msize = clnt->trans_mod->maxsize;
+		pr_info("Limiting 'msize' to %d as this is the maximum "
+			"supported by transport %s\n",
+			clnt->msize, clnt->trans_mod->name
+		);
+	}
 
 	if (clnt->msize < 4096) {
 		p9_debug(P9_DEBUG_ERROR,