linux-kernel - Re: [PATCH V3 4/4] 9p: convert to the new mount API

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Message-ID: <aOzT2-e8_p92WfP-@codewreck.org>
Date: Mon, 13 Oct 2025 19:26:35 +0900
From: Dominique Martinet <asmadeus@...ewreck.org>
To: Eric Sandeen <sandeen@...hat.com>
Cc: v9fs@...ts.linux.dev, linux-fsdevel@...r.kernel.org,
	linux-kernel@...r.kernel.org, ericvh@...nel.org, lucho@...kov.net,
	linux_oss@...debyte.com, eadavis@...com
Subject: Re: [PATCH V3 4/4] 9p: convert to the new mount API

Hi Eric,

Thanks for this V3!

I find it much cleaner, hopefully will be easier to debug :)
... Which turned out to be needed right away, trying with qemu's 9p
export "mount -t 9p -o trans=virtio tmp /mnt" apparently calls
p9_virtio_create() with fc->source == NULL, instead of the expected
"tmp" string
(FWIW I tried '-o trans=tcp 127.0.0.1' and I got the same problem in
p9_fd_create_tcp(), might be easier to test with diod if that's what you
used)

Looking at other filesystems (e.g. fs/nfs/fs_context.c but others are
the same) it looks like they all define a fsparam_string "source" option
explicitly?...

Something like this looks like it works to do (+ probably make the error
more verbose? nothing in dmesg hints at why mount returns EINVAL...)
-----
diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 6c07635f5776..999d54a0c7d9 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -34,6 +34,8 @@ struct kmem_cache *v9fs_inode_cache;
  */
 
 enum {
+	/* Mount-point source */
+	Opt_source,
 	/* Options that take integer arguments */
 	Opt_debug, Opt_dfltuid, Opt_dfltgid, Opt_afid,
 	/* String options */
@@ -82,6 +84,7 @@ static const struct constant_table p9_cache_mode[] = {
  * the client, and all the transports.
  */
 const struct fs_parameter_spec v9fs_param_spec[] = {
+	fsparam_string  ("source",      Opt_source),
 	fsparam_u32hex	("debug",	Opt_debug),
 	fsparam_uid	("dfltuid",	Opt_dfltuid),
 	fsparam_gid	("dfltgid",	Opt_dfltgid),
@@ -210,6 +213,14 @@ int v9fs_parse_param(struct fs_context *fc, struct fs_parameter *param)
 	}
 
 	switch (opt) {
+	case Opt_source:
+                if (fc->source) {
+			pr_info("p9: multiple sources not supported\n");
+			return -EINVAL;
+		}
+		fc->source = param->string;
+		param->string = NULL;
+		break;
 	case Opt_debug:
 		session_opts->debug = result.uint_32;
 #ifdef CONFIG_NET_9P_DEBUG
-----

I'll try to find some time to test a mix of actual mount options later
this week

Cheers,
-- 
Dominique Martinet | Asmadeus