fuse: add helper for asynchronous writes

This patch adds a new helper function fuse_write_fill() which makes it
possible to send WRITE requests asynchronously.

A new flag for WRITE requests is also added which indicates that this a write
from the page cache, and not a "normal" file write.

This patch is in preparation for writable mmap support.
Signed-off-by: Miklos Szeredi <mszeredi@suse.cz>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

fs/fuse/file.c

@@ -443,30 +443,37 @@ static int fuse_readpages(struct file *file, struct address_space *mapping,
 	return err;
 }
 
-static size_t fuse_send_write(struct fuse_req *req, struct file *file,
-			      struct inode *inode, loff_t pos, size_t count)
+static void fuse_write_fill(struct fuse_req *req, struct fuse_file *ff,
+			    struct inode *inode, loff_t pos, size_t count,
+			    int writepage)
 {
-	struct fuse_conn *fc = get_fuse_conn(inode);
-	struct fuse_file *ff = file->private_data;
-	struct fuse_write_in inarg;
-	struct fuse_write_out outarg;
+	struct fuse_write_in *inarg = &req->misc.write.in;
+	struct fuse_write_out *outarg = &req->misc.write.out;
 
-	memset(&inarg, 0, sizeof(struct fuse_write_in));
-	inarg.fh = ff->fh;
-	inarg.offset = pos;
-	inarg.size = count;
+	memset(inarg, 0, sizeof(struct fuse_write_in));
+	inarg->fh = ff->fh;
+	inarg->offset = pos;
+	inarg->size = count;
+	inarg->write_flags = writepage ? FUSE_WRITE_CACHE : 0;
 	req->in.h.opcode = FUSE_WRITE;
 	req->in.h.nodeid = get_node_id(inode);
 	req->in.argpages = 1;
 	req->in.numargs = 2;
 	req->in.args[0].size = sizeof(struct fuse_write_in);
-	req->in.args[0].value = &inarg;
+	req->in.args[0].value = inarg;
 	req->in.args[1].size = count;
 	req->out.numargs = 1;
 	req->out.args[0].size = sizeof(struct fuse_write_out);
-	req->out.args[0].value = &outarg;
+	req->out.args[0].value = outarg;
+}
+
+static size_t fuse_send_write(struct fuse_req *req, struct file *file,
+			      struct inode *inode, loff_t pos, size_t count)
+{
+	struct fuse_conn *fc = get_fuse_conn(inode);
+	fuse_write_fill(req, file->private_data, inode, pos, count, 0);
 	request_send(fc, req);
-	return outarg.size;
+	return req->misc.write.out.size;
 }
 
 static int fuse_write_begin(struct file *file, struct address_space *mapping,

fs/fuse/fuse_i.h

@@ -219,6 +219,10 @@ struct fuse_req {
 		struct fuse_init_in init_in;
 		struct fuse_init_out init_out;
 		struct fuse_read_in read_in;
+		struct {
+			struct fuse_write_in in;
+			struct fuse_write_out out;
+		} write;
 		struct fuse_lk_in lk_in;
 	} misc;
 

include/linux/fuse.h

@@ -119,6 +119,13 @@ struct fuse_file_lock {
  */
 #define FUSE_LK_FLOCK		(1 << 0)
 
+/**
+ * WRITE flags
+ *
+ * FUSE_WRITE_CACHE: delayed write from page cache, file handle is guessed
+ */
+#define FUSE_WRITE_CACHE	(1 << 0)
+
 enum fuse_opcode {
 	FUSE_LOOKUP	   = 1,
 	FUSE_FORGET	   = 2,  /* no reply */