ceph: handle InodeStat v8 versioned field in reply parsing

Add forward-compatible handling for the new versioned field introduced
in InodeStat v8. This patch only skips the field without using it,
preparing for future protocol extensions.

The v8 encoding adds a versioned sub-structure that needs to be properly
decoded and skipped to maintain compatibility with newer MDS versions.

Signed-off-by: Alex Markuze <amarkuze@redhat.com>
Reviewed-by: Viacheslav Dubeyko <Slava.Dubeyko@ibm.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

Author: Alex Markuze

fs/ceph/mds_client.c

@@ -232,6 +232,26 @@ static int parse_reply_info_in(void **p, void *end,
 						      info->fscrypt_file_len, bad);
 			}
 		}
+
+		/*
+		 * InodeStat encoding versions:
+		 *   v1-v7: various fields added over time
+		 *   v8: added optmetadata (versioned sub-structure containing
+		 *       optional inode metadata like charmap for case-insensitive
+		 *       filesystems). The kernel client doesn't support
+		 *       case-insensitive lookups, so we skip this field.
+		 *   v9: added subvolume_id (parsed below)
+		 */
+		if (struct_v >= 8) {
+			u32 v8_struct_len;
+
+			/* skip optmetadata versioned sub-structure */
+			ceph_decode_skip_8(p, end, bad);  /* struct_v */
+			ceph_decode_skip_8(p, end, bad);  /* struct_compat */
+			ceph_decode_32_safe(p, end, v8_struct_len, bad);
+			ceph_decode_skip_n(p, end, v8_struct_len, bad);
+		}
+
 		*p = end;
 	} else {
 		/* legacy (unversioned) struct */