[PATCH 51/67] fscache: Make fscache_write_to_cache() conditional on cookie

[David Howells]

Make fscache_write_to_cache() conditional on cookie not being NULL, rather
than merely conditional on CONFIG_FSCACHE=[ym].  The problem with the
latter is if a filesystem, say afs, has CONFIG_AFS_FSCACHE=n but calls into
this function - linkage will fail if CONFIG_FSCACHE is less than
CONFIG_AFS.  Analogous problems can affect other filesystems, e.g. 9p.

Making fscache_write_to_cache() conditional on the cookie achieves two
things:

 (1) If cookie optimises down to constant NULL, term_func is called
     directly and may be inlined and the slow path is never called.

 (2) __fscache_write_to_cache() isn't called if cookie is dynamically NULL
     - and so, in such a case, term_func is called immediately.

Signed-off-by: David Howells <dhowells at redhat.com>
---

 include/linux/fscache.h |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 847c076d05a6..ba192567d099 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -593,7 +593,7 @@ static inline void fscache_write_to_cache(struct fscache_cookie *cookie,
 					  netfs_io_terminated_t term_func,
 					  void *term_func_priv)
 {
-	if (fscache_available()) {
+	if (fscache_cookie_valid(cookie)) {
 		__fscache_write_to_cache(cookie, mapping, start, len, i_size,
 					 term_func, term_func_priv);
 	} else {