[PATCH 2/2] fscache: introduce fscache_begin_wait_operation() helper

[Jingbo Xu <jefflexu@linux.alibaba.com>]

This is a variant of fscache_wait_for_operation() except that it's
exported for users of FsCache, and thus cookie->lock is held when
checking cookie's state.

Exporting fscache_begin_operation() directly is not acceptable as it
would introduce dependency of <trace/events/fscache.h> for users of
FsCache.

Signed-off-by: Jingbo Xu <jefflexu@linux.alibaba.com>
---
 fs/fscache/io.c         |  9 +++++++++
 include/linux/fscache.h | 22 ++++++++++++++++++++++
 2 files changed, 31 insertions(+)

diff --git a/fs/fscache/io.c b/fs/fscache/io.c
index 0d2b8dec8f82..6ccc5aadf151 100644
--- a/fs/fscache/io.c
+++ b/fs/fscache/io.c
@@ -158,6 +158,15 @@ int __fscache_begin_write_operation(struct netfs_cache_resources *cres,
 }
 EXPORT_SYMBOL(__fscache_begin_write_operation);
 
+int __fscache_begin_wait_operation(struct netfs_cache_resources *cres,
+				   struct fscache_cookie *cookie,
+				   enum fscache_want_state want_state)
+{
+	return fscache_begin_operation(cres, cookie, want_state,
+				       fscache_access_io_wait);
+}
+EXPORT_SYMBOL(__fscache_begin_wait_operation);
+
 /**
  * fscache_dirty_folio - Mark folio dirty and pin a cache object for writeback
  * @mapping: The mapping the folio belongs to.
diff --git a/include/linux/fscache.h b/include/linux/fscache.h
index 8e312c8323a8..708cf8db7f46 100644
--- a/include/linux/fscache.h
+++ b/include/linux/fscache.h
@@ -171,6 +171,8 @@ extern void __fscache_resize_cookie(struct fscache_cookie *, loff_t);
 extern void __fscache_invalidate(struct fscache_cookie *, const void *, loff_t, unsigned int);
 extern int __fscache_begin_read_operation(struct netfs_cache_resources *, struct fscache_cookie *);
 extern int __fscache_begin_write_operation(struct netfs_cache_resources *, struct fscache_cookie *);
+extern int __fscache_begin_wait_operation(struct netfs_cache_resources *, struct fscache_cookie *,
+					  enum fscache_want_state want_state);
 
 extern void __fscache_write_to_cache(struct fscache_cookie *, struct address_space *,
 				     loff_t, size_t, loff_t, netfs_io_terminated_t, void *,
@@ -543,6 +545,26 @@ int fscache_begin_write_operation(struct netfs_cache_resources *cres,
 	return -ENOBUFS;
 }
 
+/**
+ * fscache_begin_wait_operation - Wait for an object become accessible
+ * @cres: The cache resources for the operation being performed
+ * @cookie: The cookie representing the cache object
+ *
+ * Returns:
+ * * 0		- Success
+ * * -ENOBUFS	- No caching available
+ * * Other error code from the cache, such as -ENOMEM.
+ */
+static inline
+int fscache_begin_wait_operation(struct netfs_cache_resources *cres,
+				 struct fscache_cookie *cookie,
+				 enum fscache_want_state want_state)
+{
+	if (fscache_cookie_enabled(cookie))
+		return __fscache_begin_wait_operation(cres, cookie, want_state);
+	return -ENOBUFS;
+}
+
 /**
  * fscache_write - Start a write to the cache.
  * @cres: The cache resources to use
-- 
2.19.1.6.gb485710b