[RFC PATCH 2/6] fs/9p: add default option for path-based inodes

[Tingmao Wang]

Add an extra option to control the inode identification behaviour, and
make path-based default.  The reasoning for this default is that the
current 9pfs already does not re-use inodes even for same qid.path, but
because of the dcache, a file kept open by a process (by e.g. open, or
having the directory as CWD) means that other processes will re-use that
inode.  If we identify inode by path by default, this behaviour is
consistent regardless of whether files are kept open or not.

In a future version, if we can negotiate with the server and be sure that
it won't give us duplicate qid.path, the default for those cases can be
qid-based (possibly re-merging commit 724a08450f74 ("fs/9p: simplify iget
to remove unnecessary paths")...?)

Signed-off-by: Tingmao Wang <m at maowtm.org>
---
 fs/9p/v9fs.c | 33 ++++++++++++++++++++++++++++++++-
 fs/9p/v9fs.h |  2 ++
 2 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 77e9c4387c1d..487532295a98 100644
--- a/fs/9p/v9fs.c
+++ b/fs/9p/v9fs.c
@@ -36,7 +36,7 @@ enum {
 	/* Options that take integer arguments */
 	Opt_debug, Opt_dfltuid, Opt_dfltgid, Opt_afid,
 	/* String options */
-	Opt_uname, Opt_remotename, Opt_cache, Opt_cachetag,
+	Opt_uname, Opt_remotename, Opt_cache, Opt_cachetag, Opt_inodeident,
 	/* Options that take no arguments */
 	Opt_nodevmap, Opt_noxattr, Opt_directio, Opt_ignoreqv,
 	/* Access options */
@@ -63,6 +63,7 @@ static const match_table_t tokens = {
 	{Opt_access, "access=%s"},
 	{Opt_posixacl, "posixacl"},
 	{Opt_locktimeout, "locktimeout=%u"},
+	{Opt_inodeident, "inodeident=%s"},
 	{Opt_err, NULL}
 };
 
@@ -149,6 +150,15 @@ int v9fs_show_options(struct seq_file *m, struct dentry *root)
 	if (v9ses->flags & V9FS_NO_XATTR)
 		seq_puts(m, ",noxattr");
 
+	switch (v9ses->flags & V9FS_INODE_IDENT_MASK) {
+	case 0:
+		seq_puts(m, ",inodeident=none");
+		break;
+	case V9FS_INODE_IDENT_PATH:
+		seq_puts(m, ",inodeident=path");
+		break;
+	}
+
 	return p9_show_client_options(m, v9ses->clnt);
 }
 
@@ -369,6 +379,25 @@ static int v9fs_parse_options(struct v9fs_session_info *v9ses, char *opts)
 			v9ses->session_lock_timeout = (long)option * HZ;
 			break;
 
+		case Opt_inodeident:
+			s = match_strdup(&args[0]);
+			if (!s) {
+				ret = -ENOMEM;
+				p9_debug(P9_DEBUG_ERROR,
+					 "problem allocating copy of inodeident arg\n");
+				goto free_and_return;
+			}
+			if (strcmp(s, "none") == 0) {
+				v9ses->flags &= ~V9FS_INODE_IDENT_MASK;
+			} else if (strcmp(s, "path") == 0) {
+				v9ses->flags |= V9FS_INODE_IDENT_PATH;
+			} else {
+				ret = -EINVAL;
+				p9_debug(P9_DEBUG_ERROR, "Unknown inodeident argument %s\n", s);
+			}
+			kfree(s);
+			break;
+
 		default:
 			continue;
 		}
@@ -423,6 +452,8 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
 		v9ses->flags |= V9FS_PROTO_2000U;
 	}
 
+	v9ses->flags |= V9FS_INODE_IDENT_PATH;
+
 	rc = v9fs_parse_options(v9ses, data);
 	if (rc < 0)
 		goto err_clnt;
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index 5c85923aa2dd..b4874fdd925e 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -31,6 +31,8 @@
 #define V9FS_ACCESS_MASK V9FS_ACCESS_ANY
 #define V9FS_ACL_MASK V9FS_POSIX_ACL
 
+#define V9FS_INODE_IDENT_MASK (V9FS_INODE_IDENT_PATH)
+
 enum p9_session_flags {
 	V9FS_PROTO_2000U      = 0x01,
 	V9FS_PROTO_2000L      = 0x02,
-- 
2.39.5