[RFC PATCH 2/5] 9p: Introduce option for negative dentry cache retention time

[Remi Pommarel <repk@triplefau.lt>]

Add support for a new mount option in v9fs that allows users to specify
the duration for which negative dentries are retained in the cache. The
retention time can be set in milliseconds using the ndentrytmo option.

For the same consistency reasons, this option should only be used in
exclusive or read-only mount scenarios, aligning with the cache=loose
usage.

Signed-off-by: Remi Pommarel <repk@triplefau.lt>
---
 fs/9p/v9fs.c | 15 ++++++++++++++-
 1 file changed, 14 insertions(+), 1 deletion(-)

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 422bd720d165..7c0c2201b151 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -34,7 +34,7 @@ struct kmem_cache *v9fs_inode_cache;
 
 enum {
 	/* Options that take integer arguments */
-	Opt_debug, Opt_dfltuid, Opt_dfltgid, Opt_afid,
+	Opt_debug, Opt_dfltuid, Opt_dfltgid, Opt_afid, Opt_ndentrytmo,
 	/* String options */
 	Opt_uname, Opt_remotename, Opt_cache, Opt_cachetag,
 	/* Options that take no arguments */
@@ -52,6 +52,7 @@ static const match_table_t tokens = {
 	{Opt_dfltuid, "dfltuid=%u"},
 	{Opt_dfltgid, "dfltgid=%u"},
 	{Opt_afid, "afid=%u"},
+	{Opt_ndentrytmo, "ndentrytmo=%d"},
 	{Opt_uname, "uname=%s"},
 	{Opt_remotename, "aname=%s"},
 	{Opt_nodevmap, "nodevmap"},
@@ -110,6 +111,8 @@ int v9fs_show_options(struct seq_file *m, struct dentry *root)
 			   from_kgid_munged(&init_user_ns, v9ses->dfltgid));
 	if (v9ses->afid != ~0)
 		seq_printf(m, ",afid=%u", v9ses->afid);
+	if (v9ses->ndentry_timeout != 0)
+		seq_printf(m, ",ndentrytmo=%d", v9ses->ndentry_timeout);
 	if (strcmp(v9ses->uname, V9FS_DEFUSER) != 0)
 		seq_printf(m, ",uname=%s", v9ses->uname);
 	if (strcmp(v9ses->aname, V9FS_DEFANAME) != 0)
@@ -251,6 +254,16 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses, char *opts)
 				v9ses->afid = option;
 			}
 			break;
+		case Opt_ndentrytmo:
+			r = match_int(&args[0], &option);
+			if (r < 0) {
+				p9_debug(P9_DEBUG_ERROR,
+					 "integer field, but no integer?\n");
+				ret = r;
+			} else {
+				v9ses->ndentry_timeout = option;
+			}
+			break;
 		case Opt_uname:
 			kfree(v9ses->uname);
 			v9ses->uname = match_strdup(&args[0]);
-- 
2.50.1