cachefiles: extract write routine

Extract the generic routine of writing data to cache files, and make it
generally available.

This will be used by the following patch implementing on-demand read
mode. Since it's called inside CacheFiles module, make the interface
generic and unrelated to netfs_cache_resources.

It is worth noting that, ki->inval_counter is not initialized after
this cleanup. It shall not make any visible difference, since
inval_counter is no longer used in the write completion routine, i.e.
cachefiles_write_complete().
Signed-off-by: Jeffle Xu <jefflexu@linux.alibaba.com>
Acked-by: David Howells <dhowells@redhat.com>
Link: https://lore.kernel.org/r/20220425122143.56815-2-jefflexu@linux.alibaba.comSigned-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>

fs/cachefiles/internal.h

@@ -201,6 +201,16 @@ extern void cachefiles_put_object(struct cachefiles_object *object,
  */
 extern bool cachefiles_begin_operation(struct netfs_cache_resources *cres,
 				       enum fscache_want_state want_state);
+extern int __cachefiles_prepare_write(struct cachefiles_object *object,
+				      struct file *file,
+				      loff_t *_start, size_t *_len,
+				      bool no_space_allocated_yet);
+extern int __cachefiles_write(struct cachefiles_object *object,
+			      struct file *file,
+			      loff_t start_pos,
+			      struct iov_iter *iter,
+			      netfs_io_terminated_t term_func,
+			      void *term_func_priv);
 
 /*
  * key.c

fs/cachefiles/io.c

@@ -277,36 +277,33 @@ static void cachefiles_write_complete(struct kiocb *iocb, long ret)
 /*
  * Initiate a write to the cache.
  */
-static int cachefiles_write(struct netfs_cache_resources *cres,
+int __cachefiles_write(struct cachefiles_object *object,
+		       struct file *file,
 		       loff_t start_pos,
 		       struct iov_iter *iter,
 		       netfs_io_terminated_t term_func,
 		       void *term_func_priv)
 {
-	struct cachefiles_object *object;
 	struct cachefiles_cache *cache;
 	struct cachefiles_kiocb *ki;
 	struct inode *inode;
-	struct file *file;
 	unsigned int old_nofs;
-	ssize_t ret = -ENOBUFS;
+	ssize_t ret;
 	size_t len = iov_iter_count(iter);
 
-	if (!fscache_wait_for_operation(cres, FSCACHE_WANT_WRITE))
-		goto presubmission_error;
 	fscache_count_write();
-	object = cachefiles_cres_object(cres);
 	cache = object->volume->cache;
-	file = cachefiles_cres_file(cres);
 
 	_enter("%pD,%li,%llx,%zx/%llx",
 	       file, file_inode(file)->i_ino, start_pos, len,
 	       i_size_read(file_inode(file)));
 
-	ret = -ENOMEM;
 	ki = kzalloc(sizeof(struct cachefiles_kiocb), GFP_KERNEL);
-	if (!ki)
-		goto presubmission_error;
+	if (!ki) {
+		if (term_func)
+			term_func(term_func_priv, -ENOMEM, false);
+		return -ENOMEM;
+	}
 
 	refcount_set(&ki->ki_refcnt, 2);
 	ki->iocb.ki_filp	= file;
@@ -314,7 +311,6 @@ static int cachefiles_write(struct netfs_cache_resources *cres,
 	ki->iocb.ki_flags	= IOCB_DIRECT | IOCB_WRITE;
 	ki->iocb.ki_ioprio	= get_current_ioprio();
 	ki->object		= object;
-	ki->inval_counter	= cres->inval_counter;
 	ki->start		= start_pos;
 	ki->len			= len;
 	ki->term_func		= term_func;
@@ -369,11 +365,24 @@ static int cachefiles_write(struct netfs_cache_resources *cres,
 	cachefiles_put_kiocb(ki);
 	_leave(" = %zd", ret);
 	return ret;
+}
 
-presubmission_error:
+static int cachefiles_write(struct netfs_cache_resources *cres,
+			    loff_t start_pos,
+			    struct iov_iter *iter,
+			    netfs_io_terminated_t term_func,
+			    void *term_func_priv)
+{
+	if (!fscache_wait_for_operation(cres, FSCACHE_WANT_WRITE)) {
 		if (term_func)
-		term_func(term_func_priv, ret, false);
-	return ret;
+			term_func(term_func_priv, -ENOBUFS, false);
+		return -ENOBUFS;
+	}
+
+	return __cachefiles_write(cachefiles_cres_object(cres),
+				  cachefiles_cres_file(cres),
+				  start_pos, iter,
+				  term_func, term_func_priv);
 }
 
 /*
@@ -484,13 +493,12 @@ static enum netfs_io_source cachefiles_prepare_read(struct netfs_io_subrequest *
 /*
  * Prepare for a write to occur.
  */
-static int __cachefiles_prepare_write(struct netfs_cache_resources *cres,
-				      loff_t *_start, size_t *_len, loff_t i_size,
+int __cachefiles_prepare_write(struct cachefiles_object *object,
+			       struct file *file,
+			       loff_t *_start, size_t *_len,
 			       bool no_space_allocated_yet)
 {
-	struct cachefiles_object *object = cachefiles_cres_object(cres);
 	struct cachefiles_cache *cache = object->volume->cache;
-	struct file *file = cachefiles_cres_file(cres);
 	loff_t start = *_start, pos;
 	size_t len = *_len, down;
 	int ret;
@@ -577,7 +585,8 @@ static int cachefiles_prepare_write(struct netfs_cache_resources *cres,
 	}
 
 	cachefiles_begin_secure(cache, &saved_cred);
-	ret = __cachefiles_prepare_write(cres, _start, _len, i_size,
+	ret = __cachefiles_prepare_write(object, cachefiles_cres_file(cres),
+					 _start, _len,
 					 no_space_allocated_yet);
 	cachefiles_end_secure(cache, saved_cred);
 	return ret;