msg: include compat_version in version header

header.version is the version we encoded.
header.compat_version is the oldest version of code that can decode it.

If the value is 0, we don't know anything about backward compatibility.

Signed-off-by: Sage Weil <sage.weil@dreamhost.com>

diff --git a/src/include/msgr.h b/src/include/msgr.h
index f53c35b37b16c6243d66a0bc172f73e4a494ef93..0ac33946c63579500ed96dab1cd0d0139a4c91bc 100644 (file)
--- a/src/include/msgr.h
+++ b/src/include/msgr.h
@@ -156,7 +156,10 @@ struct ceph_msg_header {
                             receiver: mask against ~PAGE_MASK */
 
        struct ceph_entity_name src;
-       __le32 reserved;
+
+       /* oldest code we think can decode this.  unknown if zero. */
+       __le16 compat_version;
+       __le16 reserved;
        __le32 crc;       /* header crc32c */
 } __attribute__ ((packed));