From 72fe25e3460c8673984370208e0e6261101372d6 Mon Sep 17 00:00:00 2001 From: Alex Elder Date: Wed, 30 Jan 2013 11:13:33 -0600 Subject: [PATCH] libceph: add a compatibility check interface An upcoming change implements semantic change that could lead to a crash if an old version of the libceph kernel module is used with a new version of the rbd kernel module. In order to preclude that possibility, this adds a compatibilty check interface. If this interface doesn't exist, the modules are obviously not compatible. But if it does exist, this provides a way of letting the caller know whether it will operate properly with this libceph module. Perhaps confusingly, it returns false right now. The semantic change mentioned above will make it return true. This resolves: http://tracker.ceph.com/issues/3800 Signed-off-by: Alex Elder Reviewed-by: Josh Durgin --- include/linux/ceph/libceph.h | 2 ++ net/ceph/ceph_common.c | 16 ++++++++++++++++ 2 files changed, 18 insertions(+) diff --git a/include/linux/ceph/libceph.h b/include/linux/ceph/libceph.h index 084d3c622b12..c44275ab375c 100644 --- a/include/linux/ceph/libceph.h +++ b/include/linux/ceph/libceph.h @@ -193,6 +193,8 @@ static inline int calc_pages_for(u64 off, u64 len) } /* ceph_common.c */ +extern bool libceph_compatible(void *data); + extern const char *ceph_msg_type_name(int type); extern int ceph_check_fsid(struct ceph_client *client, struct ceph_fsid *fsid); extern struct kmem_cache *ceph_inode_cachep; diff --git a/net/ceph/ceph_common.c b/net/ceph/ceph_common.c index ee71ea26777a..a98c03ff853f 100644 --- a/net/ceph/ceph_common.c +++ b/net/ceph/ceph_common.c @@ -26,6 +26,22 @@ #include "crypto.h" +/* + * Module compatibility interface. For now it doesn't do anything, + * but its existence signals a certain level of functionality. + * + * The data buffer is used to pass information both to and from + * libceph. The return value indicates whether libceph determines + * it is compatible with the caller (from another kernel module), + * given the provided data. + * + * The data pointer can be null. + */ +bool libceph_compatible(void *data) +{ + return false; +} +EXPORT_SYMBOL(libceph_compatible); /* * find filename portion of a path (/foo/bar/baz -> baz)