fuse: make request allocations for background processing explicit

There are two types of processing requests in FUSE: synchronous (via
fuse_request_send()) and asynchronous (via adding to fc->bg_queue).

Fortunately, the type of processing is always known in advance, at the time
of request allocation. This preparatory patch utilizes this fact making
fuse_get_req() aware about the type. Next patches will use it.
Signed-off-by: Maxim Patlasov <mpatlasov@parallels.com>
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>

fs/fuse/cuse.c

@@ -422,7 +422,7 @@ static int cuse_send_init(struct cuse_conn *cc)
 
 	BUILD_BUG_ON(CUSE_INIT_INFO_MAX > PAGE_SIZE);
 
-	req = fuse_get_req(fc, 1);
+	req = fuse_get_req_for_background(fc, 1);
 	if (IS_ERR(req)) {
 		rc = PTR_ERR(req);
 		goto err;

fs/fuse/dev.c

@@ -130,7 +130,8 @@ static void fuse_req_init_context(struct fuse_req *req)
 	req->in.h.pid = current->pid;
 }
 
-struct fuse_req *fuse_get_req(struct fuse_conn *fc, unsigned npages)
+static struct fuse_req *__fuse_get_req(struct fuse_conn *fc, unsigned npages,
+				       bool for_background)
 {
 	struct fuse_req *req;
 	sigset_t oldset;
@@ -156,14 +157,27 @@ struct fuse_req *fuse_get_req(struct fuse_conn *fc, unsigned npages)
 
 	fuse_req_init_context(req);
 	req->waiting = 1;
+	req->background = for_background;
 	return req;
 
  out:
 	atomic_dec(&fc->num_waiting);
 	return ERR_PTR(err);
 }
+
+struct fuse_req *fuse_get_req(struct fuse_conn *fc, unsigned npages)
+{
+	return __fuse_get_req(fc, npages, false);
+}
 EXPORT_SYMBOL_GPL(fuse_get_req);
 
+struct fuse_req *fuse_get_req_for_background(struct fuse_conn *fc,
+					     unsigned npages)
+{
+	return __fuse_get_req(fc, npages, true);
+}
+EXPORT_SYMBOL_GPL(fuse_get_req_for_background);
+
 /*
  * Return request in fuse_file->reserved_req.  However that may
  * currently be in use.  If that is the case, wait for it to become
@@ -232,6 +246,7 @@ struct fuse_req *fuse_get_req_nofail_nopages(struct fuse_conn *fc,
 
 	fuse_req_init_context(req);
 	req->waiting = 1;
+	req->background = 0;
 	return req;
 }
 
@@ -442,6 +457,7 @@ __acquires(fc->lock)
 
 static void __fuse_request_send(struct fuse_conn *fc, struct fuse_req *req)
 {
+	BUG_ON(req->background);
 	spin_lock(&fc->lock);
 	if (!fc->connected)
 		req->out.h.error = -ENOTCONN;
@@ -469,7 +485,7 @@ EXPORT_SYMBOL_GPL(fuse_request_send);
 static void fuse_request_send_nowait_locked(struct fuse_conn *fc,
 					    struct fuse_req *req)
 {
-	req->background = 1;
+	BUG_ON(!req->background);
 	fc->num_background++;
 	if (fc->num_background == fc->max_background)
 		fc->blocked = 1;

fs/fuse/file.c

@@ -126,11 +126,13 @@ static void fuse_file_put(struct fuse_file *ff, bool sync)
 		struct fuse_req *req = ff->reserved_req;
 
 		if (sync) {
+			req->background = 0;
 			fuse_request_send(ff->fc, req);
 			path_put(&req->misc.release.path);
 			fuse_put_request(ff->fc, req);
 		} else {
 			req->end = fuse_release_end;
+			req->background = 1;
 			fuse_request_send_background(ff->fc, req);
 		}
 		kfree(ff);
@@ -282,6 +284,7 @@ void fuse_sync_release(struct fuse_file *ff, int flags)
 	WARN_ON(atomic_read(&ff->count) > 1);
 	fuse_prepare_release(ff, flags, FUSE_RELEASE);
 	ff->reserved_req->force = 1;
+	ff->reserved_req->background = 0;
 	fuse_request_send(ff->fc, ff->reserved_req);
 	fuse_put_request(ff->fc, ff->reserved_req);
 	kfree(ff);
@@ -661,7 +664,12 @@ static int fuse_readpages_fill(void *_data, struct page *page)
 		int nr_alloc = min_t(unsigned, data->nr_pages,
 				     FUSE_MAX_PAGES_PER_REQ);
 		fuse_send_readpages(req, data->file);
-		data->req = req = fuse_get_req(fc, nr_alloc);
+		if (fc->async_read)
+			req = fuse_get_req_for_background(fc, nr_alloc);
+		else
+			req = fuse_get_req(fc, nr_alloc);
+
+		data->req = req;
 		if (IS_ERR(req)) {
 			unlock_page(page);
 			return PTR_ERR(req);
@@ -696,6 +704,9 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
 
 	data.file = file;
 	data.inode = inode;
+	if (fc->async_read)
+		data.req = fuse_get_req_for_background(fc, nr_alloc);
+	else
 		data.req = fuse_get_req(fc, nr_alloc);
 	data.nr_pages = nr_pages;
 	err = PTR_ERR(data.req);
@@ -1375,6 +1386,7 @@ static int fuse_writepage_locked(struct page *page)
 	if (!req)
 		goto err;
 
+	req->background = 1; /* writeback always goes to bg_queue */
 	tmp_page = alloc_page(GFP_NOFS | __GFP_HIGHMEM);
 	if (!tmp_page)
 		goto err_free;

fs/fuse/fuse_i.h

@@ -708,6 +708,8 @@ void fuse_request_free(struct fuse_req *req);
  * caller should specify # elements in req->pages[] explicitly
  */
 struct fuse_req *fuse_get_req(struct fuse_conn *fc, unsigned npages);
+struct fuse_req *fuse_get_req_for_background(struct fuse_conn *fc,
+					     unsigned npages);
 
 /**
  * Get a request, may fail with -ENOMEM,

fs/fuse/inode.c

@@ -346,6 +346,7 @@ static void fuse_send_destroy(struct fuse_conn *fc)
 		fc->destroy_req = NULL;
 		req->in.h.opcode = FUSE_DESTROY;
 		req->force = 1;
+		req->background = 0;
 		fuse_request_send(fc, req);
 		fuse_put_request(fc, req);
 	}
@@ -1043,6 +1044,7 @@ static int fuse_fill_super(struct super_block *sb, void *data, int silent)
 	init_req = fuse_request_alloc(0);
 	if (!init_req)
 		goto err_put_root;
+	init_req->background = 1;
 
 	if (is_bdev) {
 		fc->destroy_req = fuse_request_alloc(0);