[PATCH v2 2/7] fs/9p: add option for path-based inodes

[Tingmao Wang]

By this point we have two ways to test for inode reuse - qid and qid+path.
By default, uncached mode uses qid+path and cached mode uses qid (and in
fact does not support qid+path).  This patch adds the option to control
the behaviour for uncached mode.

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.

Signed-off-by: Tingmao Wang <m at maowtm.org>
Cc: "Mickaël Salaün" <mic at digikod.net>
Cc: "Günther Noack" <gnoack at google.com>

---
Changes since v1:
- Removed inodeident=none and instead supports inodeident=qid.  This means
  that there is no longer an option to not re-use inodes at all.

- No longer supports inodeident=path on cached mode, checks added at
  option init time.

- Added explicit bits for both V9FS_INODE_IDENT_PATH and
  V9FS_INODE_IDENT_QID, in order to set a default based on cache bits when
  neither are set explicitly by the user.

 fs/9p/v9fs.c | 59 +++++++++++++++++++++++++++++++++++++++++++++++++++-
 fs/9p/v9fs.h |  3 +++
 2 files changed, 61 insertions(+), 1 deletion(-)

diff --git a/fs/9p/v9fs.c b/fs/9p/v9fs.c
index 77e9c4387c1d..f87d6680b85a 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 +150,21 @@ 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 V9FS_INODE_IDENT_QID:
+		seq_puts(m, ",inodeident=qid");
+		break;
+	case V9FS_INODE_IDENT_PATH:
+		seq_puts(m, ",inodeident=path");
+		break;
+	default:
+		/*
+		 * Unspecified, will be set later in v9fs_session_init depending on
+		 * cache setting
+		 */
+		break;
+	}
+
 	return p9_show_client_options(m, v9ses->clnt);
 }
 
@@ -369,6 +385,26 @@ 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;
+			}
+			v9ses->flags &= ~V9FS_INODE_IDENT_MASK;
+			if (strcmp(s, "qid") == 0) {
+				v9ses->flags |= V9FS_INODE_IDENT_QID;
+			} 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;
 		}
@@ -393,6 +429,7 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
 {
 	struct p9_fid *fid;
 	int rc = -ENOMEM;
+	bool cached;
 
 	v9ses->uname = kstrdup(V9FS_DEFUSER, GFP_KERNEL);
 	if (!v9ses->uname)
@@ -427,6 +464,26 @@ struct p9_fid *v9fs_session_init(struct v9fs_session_info *v9ses,
 	if (rc < 0)
 		goto err_clnt;
 
+	cached = v9ses->cache & (CACHE_META | CACHE_LOOSE);
+
+	if (cached && v9ses->flags & V9FS_INODE_IDENT_PATH) {
+		rc = -EINVAL;
+		p9_debug(P9_DEBUG_ERROR,
+			 "inodeident=path not supported in cached mode\n");
+		goto err_clnt;
+	}
+
+	if (!(v9ses->flags & V9FS_INODE_IDENT_MASK)) {
+		/* Unspecified - use default */
+		if (cached) {
+			/* which is qid in cached mode (path not supported) */
+			v9ses->flags |= V9FS_INODE_IDENT_QID;
+		} else {
+			/* ...or path in uncached mode */
+			v9ses->flags |= V9FS_INODE_IDENT_PATH;
+		}
+	}
+
 	v9ses->maxdata = v9ses->clnt->msize - P9_IOHDRSZ;
 
 	if (!v9fs_proto_dotl(v9ses) &&
diff --git a/fs/9p/v9fs.h b/fs/9p/v9fs.h
index 134b55a605be..b4e738c1bba5 100644
--- a/fs/9p/v9fs.h
+++ b/fs/9p/v9fs.h
@@ -43,8 +43,11 @@ enum p9_session_flags {
 	V9FS_DIRECT_IO        = 0x100,
 	V9FS_SYNC             = 0x200,
 	V9FS_INODE_IDENT_PATH = 0x400,
+	V9FS_INODE_IDENT_QID  = 0x800,
 };
 
+#define V9FS_INODE_IDENT_MASK (V9FS_INODE_IDENT_PATH | V9FS_INODE_IDENT_QID)
+
 /**
  * enum p9_cache_shortcuts - human readable cache preferences
  * @CACHE_SC_NONE: disable all caches
-- 
2.51.0