export generic_perform_write(), start getting rid of generic_file_buffer_write()

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

include/linux/fs.h

@@ -48,6 +48,7 @@ struct cred;
 struct swap_info_struct;
 struct seq_file;
 struct workqueue_struct;
+struct iov_iter;
 
 extern void __init inode_init(void);
 extern void __init inode_init_early(void);
@@ -2396,6 +2397,7 @@ extern ssize_t __generic_file_aio_write(struct kiocb *, const struct iovec *, un
 extern ssize_t generic_file_aio_write(struct kiocb *, const struct iovec *, unsigned long, loff_t);
 extern ssize_t generic_file_direct_write(struct kiocb *, const struct iovec *,
 		unsigned long *, loff_t, size_t, size_t);
+extern ssize_t generic_perform_write(struct file *, struct iov_iter *, loff_t);
 extern ssize_t generic_file_buffered_write(struct kiocb *, const struct iovec *,
 		unsigned long, loff_t, size_t, ssize_t);
 extern ssize_t do_sync_read(struct file *filp, char __user *buf, size_t len, loff_t *ppos);

mm/filemap.c

@@ -2092,7 +2092,7 @@ found:
 }
 EXPORT_SYMBOL(grab_cache_page_write_begin);
 
-static ssize_t generic_perform_write(struct file *file,
+ssize_t generic_perform_write(struct file *file,
 				struct iov_iter *i, loff_t pos)
 {
 	struct address_space *mapping = file->f_mapping;
@@ -2180,6 +2180,7 @@ again:
 
 	return written ? written : status;
 }
+EXPORT_SYMBOL(generic_perform_write);
 
 ssize_t
 generic_file_buffered_write(struct kiocb *iocb, const struct iovec *iov,
@@ -2230,8 +2231,10 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	size_t count;		/* after file limit checks */
 	struct inode 	*inode = mapping->host;
 	loff_t		pos = iocb->ki_pos;
-	ssize_t		written;
+	ssize_t		written = 0;
 	ssize_t		err;
+	ssize_t		status;
+	struct iov_iter from;
 
 	ocount = 0;
 	err = generic_segment_checks(iov, &nr_segs, &ocount, VERIFY_READ);
@@ -2242,8 +2245,6 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = mapping->backing_dev_info;
-	written = 0;
-
 	err = generic_write_checks(file, &pos, &count, S_ISBLK(inode->i_mode));
 	if (err)
 		goto out;
@@ -2259,44 +2260,47 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 	if (err)
 		goto out;
 
+	iov_iter_init(&from, iov, nr_segs, count, 0);
+
 	/* coalesce the iovecs and go direct-to-BIO for O_DIRECT */
 	if (unlikely(file->f_flags & O_DIRECT)) {
 		loff_t endbyte;
-		ssize_t written_buffered;
 
-		written = generic_file_direct_write(iocb, iov, &nr_segs, pos,
+		written = generic_file_direct_write(iocb, iov, &from.nr_segs, pos,
 							count, ocount);
 		if (written < 0 || written == count)
 			goto out;
+		iov_iter_advance(&from, written);
+
 		/*
 		 * direct-io write to a hole: fall through to buffered I/O
 		 * for completing the rest of the request.
 		 */
 		pos += written;
 		count -= written;
-		written_buffered = generic_file_buffered_write(iocb, iov,
-						nr_segs, pos, count, written);
+
+		status = generic_perform_write(file, &from, pos);
 		/*
-		 * If generic_file_buffered_write() retuned a synchronous error
+		 * If generic_perform_write() returned a synchronous error
 		 * then we want to return the number of bytes which were
 		 * direct-written, or the error code if that was zero.  Note
 		 * that this differs from normal direct-io semantics, which
 		 * will return -EFOO even if some bytes were written.
 		 */
-		if (written_buffered < 0) {
-			err = written_buffered;
+		if (unlikely(status < 0) && !written) {
+			err = status;
 			goto out;
 		}
-
+		iocb->ki_pos = pos + status;
 		/*
 		 * We need to ensure that the page cache pages are written to
 		 * disk and invalidated to preserve the expected O_DIRECT
 		 * semantics.
 		 */
-		endbyte = pos + written_buffered - written - 1;
+		endbyte = pos + status - 1;
 		err = filemap_write_and_wait_range(file->f_mapping, pos, endbyte);
 		if (err == 0) {
-			written = written_buffered;
+			written += status;
 			invalidate_mapping_pages(mapping,
 						 pos >> PAGE_CACHE_SHIFT,
 						 endbyte >> PAGE_CACHE_SHIFT);
@@ -2307,8 +2311,9 @@ ssize_t __generic_file_aio_write(struct kiocb *iocb, const struct iovec *iov,
 			 */
 		}
 	} else {
-		written = generic_file_buffered_write(iocb, iov, nr_segs,
-				pos, count, written);
+		written = generic_perform_write(file, &from, pos);
+		if (likely(written >= 0))
+			iocb->ki_pos = pos + written;
 	}
 out:
 	current->backing_dev_info = NULL;