LINUX: Avoid check for key_type.match existence

Commit b5de4a9f removed our key_type 'match' function for kernels that
do not have such a 'match' function pointer. However, this added a
configure test where we are supposed to fail for the "new" behavior,
which is discouraged.

This causes an actual problem, because this test will fail on at least
RHEL5, due to arguably unrelated reasons (the header file for the
relevant struct is in key.h instead of key-type.h). And so, in that
situation we avoid defining a 'match' function callback, meaning our
'match' function callback is NULL, which causes a panic when we try to
actually look up keys for a PAG.

To fix this, transform the 'match' config test into one where we
succeed for the "new" behavior. We do this by testing for the
existence of the new functionality that replaced the old 'match'
function, which is the match_preparse function (specifically, the
'cmp' field in the structure accepted by match_preparse). This should
cause unrelated compilation errors to cause us to revert to the "old"
behavior instead of the "new" behavior. At worst, this should cause
build issues if we get the config test wrong (since we will try to use
the 'match' function definition that does not exist), instead of
panicing at runtime.

Note that while we test for key_type.match_preparse, we don't actually
use that function, since our 'match' functionality is the same as the
default behavior (according to b5de4a9f). So, we can avoid defining
any such function for newer kernels.

Thanks to Stephan Wiesand for bisecting this issue.

Change-Id: If6f93d6b5340fa738a55adeb7778d26ff5dbacc1
Reviewed-on: http://gerrit.openafs.org/11589
Reviewed-by: Marc Dionne <marc.c.dionne@gmail.com>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>

diff --git a/acinclude.m4 b/acinclude.m4
index 5e753ec4d1d6b2d3f06739f7ff374aa3055e003e..97c2d79d67bacb26197967dc2bed720eee13cd91 100644 (file)
--- a/acinclude.m4
+++ b/acinclude.m4
@@ -891,7 +891,7 @@ case $AFS_SYSNAME in *_linux* | *_umlinux*)
                 AC_CHECK_LINUX_STRUCT([file_system_type], [mount], [fs.h])
                 AC_CHECK_LINUX_STRUCT([inode_operations], [truncate], [fs.h])
                 AC_CHECK_LINUX_STRUCT([key_type], [instantiate_prep], [key-type.h])
-                AC_CHECK_LINUX_STRUCT([key_type], [match], [key-type.h])
+                AC_CHECK_LINUX_STRUCT([key_type], [match_preparse], [key-type.h])
                 AC_CHECK_LINUX_STRUCT([key_type], [preparse], [key-type.h])
                 AC_CHECK_LINUX_STRUCT([nameidata], [path], [namei.h])
                 AC_CHECK_LINUX_STRUCT([proc_dir_entry], [owner], [proc_fs.h])

diff --git a/src/afs/LINUX/osi_groups.c b/src/afs/LINUX/osi_groups.c
index f1d97a664189b593adf7bf7b5df9a7dfc9bc53eb..3b068e5ce23bd827b0f8bee9288d6cbc5df3b958 100644 (file)
--- a/src/afs/LINUX/osi_groups.c
+++ b/src/afs/LINUX/osi_groups.c
@@ -498,7 +498,13 @@ error:
     return code;
 }
 
-#if defined(STRUCT_KEY_TYPE_HAS_MATCH)
+#if !defined(STRUCT_KEY_TYPE_HAS_MATCH_PREPARSE)
+/* Note that we only define a ->match function if struct
+ * key_type.match_preparse does _not_ exist. If key_type.match_preparse does
+ * exist, we would use that to specify an alternative comparison function; but
+ * since we just rely on default behavior, we don't need to actually specify
+ * one. But for kernels with no such match_preparse function, we need to
+ * specify a 'match' function, since there is no default. */
 static int afs_pag_match(const struct key *key, const void *description)
 {
        return strcmp(key->description, description) == 0;
@@ -529,7 +535,7 @@ struct key_type key_type_afs_pag =
 #else
     .instantiate = afs_pag_instantiate,
 #endif
-#if defined(STRUCT_KEY_TYPE_HAS_MATCH)
+#if !defined(STRUCT_KEY_TYPE_HAS_MATCH_PREPARSE)
     .match       = afs_pag_match,
 #endif
     .destroy     = afs_pag_destroy,