From: Christoph Hellwig <hch@lst.de>

commit 44fff0fa08ec5a6d9d5fb05443a36d854d0ece4d upstream.

Add a helper dealing with handling the syncing of a buffered write
fallback for direct I/O.

Link: https://lkml.kernel.org/r/20230601145904.1385409-10-hch@lst.de
Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Damien Le Moal <dlemoal@kernel.org>
Reviewed-by: Miklos Szeredi <mszeredi@redhat.com>
Reviewed-by: Darrick J. Wong <djwong@kernel.org>
Cc: Al Viro <viro@zeniv.linux.org.uk>
Cc: Andreas Gruenbacher <agruenba@redhat.com>
Cc: Anna Schumaker <anna@kernel.org>
Cc: Chao Yu <chao@kernel.org>
Cc: Christian Brauner <brauner@kernel.org>
Cc: Hannes Reinecke <hare@suse.de>
Cc: Ilya Dryomov <idryomov@gmail.com>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Jens Axboe <axboe@kernel.dk>
Cc: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Cc: Matthew Wilcox <willy@infradead.org>
Cc: Miklos Szeredi <miklos@szeredi.hu>
Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Trond Myklebust <trond.myklebust@hammerspace.com>
Cc: Xiubo Li <xiubli@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
[backing_dev_info still being used here. do small changes to the patch
to keep the out label. Which means replacing all returns to goto out.]
Signed-off-by: Mahmoud Adam <mngyadam@amazon.de>
---
 fs/libfs.c         | 41 +++++++++++++++++++++++++++++++
 include/linux/fs.h |  2 ++
 mm/filemap.c       | 61 +++++++++++-----------------------------------
 3 files changed, 57 insertions(+), 47 deletions(-)

diff --git a/fs/libfs.c b/fs/libfs.c
index cbd42d76fbd018..a5bbe8e31d6616 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1582,3 +1582,44 @@ bool inode_maybe_inc_iversion(struct inode *inode, bool force)
 	return true;
 }
 EXPORT_SYMBOL(inode_maybe_inc_iversion);
+
+ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
+		ssize_t direct_written, ssize_t buffered_written)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	loff_t pos = iocb->ki_pos - buffered_written;
+	loff_t end = iocb->ki_pos - 1;
+	int err;
+
+	/*
+	 * If the buffered write fallback returned an error, we want to return
+	 * the number of bytes which were written by direct I/O, 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 (unlikely(buffered_written < 0)) {
+		if (direct_written)
+			return direct_written;
+		return buffered_written;
+	}
+
+	/*
+	 * We need to ensure that the page cache pages are written to disk and
+	 * invalidated to preserve the expected O_DIRECT semantics.
+	 */
+	err = filemap_write_and_wait_range(mapping, pos, end);
+	if (err < 0) {
+		/*
+		 * We don't know how much we wrote, so just return the number of
+		 * bytes which were direct-written
+		 */
+		if (direct_written)
+			return direct_written;
+		return err;
+	}
+	invalidate_mapping_pages(mapping, pos >> PAGE_SHIFT, end >> PAGE_SHIFT);
+	return direct_written + buffered_written;
+}
+EXPORT_SYMBOL_GPL(direct_write_fallback);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 4e8a3e4f894c0f..02c83cd07d4f20 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3278,6 +3278,8 @@ extern ssize_t __generic_file_write_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t generic_file_write_iter(struct kiocb *, struct iov_iter *);
 extern ssize_t generic_file_direct_write(struct kiocb *, struct iov_iter *);
 ssize_t generic_perform_write(struct kiocb *, struct iov_iter *);
+ssize_t direct_write_fallback(struct kiocb *iocb, struct iov_iter *iter,
+		ssize_t direct_written, ssize_t buffered_written);
 
 ssize_t vfs_iter_read(struct file *file, struct iov_iter *iter, loff_t *ppos,
 		rwf_t flags);
diff --git a/mm/filemap.c b/mm/filemap.c
index e2045266d2f2c9..b77f534dfad35a 100644
--- a/mm/filemap.c
+++ b/mm/filemap.c
@@ -3923,25 +3923,21 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 {
 	struct file *file = iocb->ki_filp;
 	struct address_space *mapping = file->f_mapping;
-	struct inode 	*inode = mapping->host;
-	ssize_t		written = 0;
-	ssize_t		err;
-	ssize_t		status;
+	struct inode *inode = mapping->host;
+	ssize_t ret;
 
 	/* We can write back this queue in page reclaim */
 	current->backing_dev_info = inode_to_bdi(inode);
-	err = file_remove_privs(file);
-	if (err)
+	ret = file_remove_privs(file);
+	if (ret)
 		goto out;
 
-	err = file_update_time(file);
-	if (err)
+	ret = file_update_time(file);
+	if (ret)
 		goto out;
 
 	if (iocb->ki_flags & IOCB_DIRECT) {
-		loff_t pos, endbyte;
-
-		written = generic_file_direct_write(iocb, from);
+		ret = generic_file_direct_write(iocb, from);
 		/*
 		 * If the write stopped short of completing, fall back to
 		 * buffered writes.  Some filesystems do this for writes to
@@ -3949,46 +3945,17 @@ ssize_t __generic_file_write_iter(struct kiocb *iocb, struct iov_iter *from)
 		 * not succeed (even if it did, DAX does not handle dirty
 		 * page-cache pages correctly).
 		 */
-		if (written < 0 || !iov_iter_count(from) || IS_DAX(inode))
+		if (ret < 0 || !iov_iter_count(from) || IS_DAX(inode))
 			goto out;
-
-		pos = iocb->ki_pos;
-		status = generic_perform_write(iocb, from);
-		/*
-		 * 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 (unlikely(status < 0)) {
-			err = status;
-			goto out;
-		}
-		/*
-		 * We need to ensure that the page cache pages are written to
-		 * disk and invalidated to preserve the expected O_DIRECT
-		 * semantics.
-		 */
-		endbyte = pos + status - 1;
-		err = filemap_write_and_wait_range(mapping, pos, endbyte);
-		if (err == 0) {
-			written += status;
-			invalidate_mapping_pages(mapping,
-						 pos >> PAGE_SHIFT,
-						 endbyte >> PAGE_SHIFT);
-		} else {
-			/*
-			 * We don't know how much we wrote, so just return
-			 * the number of bytes which were direct-written
-			 */
-		}
-	} else {
-		written = generic_perform_write(iocb, from);
+		ret = direct_write_fallback(iocb, from, ret,
+				generic_perform_write(iocb, from));
+		goto out;
 	}
+
+	ret = generic_perform_write(iocb, from);
 out:
 	current->backing_dev_info = NULL;
-	return written ? written : err;
+	return ret;
 }
 EXPORT_SYMBOL(__generic_file_write_iter);
 
-- 
2.47.3




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