[PATCH 08/15] btrfs: basic direct read operation

[Goldwyn Rodrigues <rgoldwyn@suse.de>]

From: Goldwyn Rodrigues <rgoldwyn@suse.com>

Add btrfs_dio_iomap_ops for iomap.begin() function. In order to
accomodate dio reads, add a new function btrfs_file_read_iter()
which would call btrfs_dio_iomap_read() for DIO reads and
fallback to generic_file_buffered_read otherwise.

Changed parameter written in generic_file_buffered_read() to
already_read.

Signed-off-by: Goldwyn Rodrigues <rgoldwyn@suse.com>
---
 fs/btrfs/ctree.h |  2 ++
 fs/btrfs/file.c  | 13 ++++++++++++-
 fs/btrfs/iomap.c | 20 ++++++++++++++++++++
 3 files changed, 34 insertions(+), 1 deletion(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 9c501c7826b4..5ca3a365e639 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -3243,7 +3243,9 @@ int btrfs_fdatawrite_range(struct inode *inode, loff_t start, loff_t end);
 loff_t btrfs_remap_file_range(struct file *file_in, loff_t pos_in,
 			      struct file *file_out, loff_t pos_out,
 			      loff_t len, unsigned int remap_flags);
+/* iomap.c */
 size_t btrfs_buffered_iomap_write(struct kiocb *iocb, struct iov_iter *from);
+ssize_t btrfs_dio_iomap_read(struct kiocb *iocb, struct iov_iter *to);
 
 /* tree-defrag.c */
 int btrfs_defrag_leaves(struct btrfs_trans_handle *trans,
diff --git a/fs/btrfs/file.c b/fs/btrfs/file.c
index f7087e28ac08..e7f67d514ba8 100644
--- a/fs/btrfs/file.c
+++ b/fs/btrfs/file.c
@@ -2839,9 +2839,20 @@ static int btrfs_file_open(struct inode *inode, struct file *filp)
 	return generic_file_open(inode, filp);
 }
 
+static ssize_t btrfs_file_read_iter(struct kiocb *iocb, struct iov_iter *to)
+{
+	ssize_t ret = 0;
+	if (iocb->ki_flags & IOCB_DIRECT)
+		ret = btrfs_dio_iomap_read(iocb, to);
+	if (ret < 0)
+		return ret;
+
+	return generic_file_buffered_read(iocb, to, ret);
+}
+
 const struct file_operations btrfs_file_operations = {
 	.llseek		= btrfs_file_llseek,
-	.read_iter      = generic_file_read_iter,
+	.read_iter      = btrfs_file_read_iter,
 	.splice_read	= generic_file_splice_read,
 	.write_iter	= btrfs_file_write_iter,
 	.mmap		= btrfs_file_mmap,
diff --git a/fs/btrfs/iomap.c b/fs/btrfs/iomap.c
index f8fa34105838..6b633c483dba 100644
--- a/fs/btrfs/iomap.c
+++ b/fs/btrfs/iomap.c
@@ -421,3 +421,23 @@ size_t btrfs_buffered_iomap_write(struct kiocb *iocb, struct iov_iter *from)
 	return written;
 }
 
+static int btrfs_dio_iomap_begin(struct inode *inode, loff_t pos,
+		loff_t length, unsigned flags, struct iomap *iomap,
+		struct iomap *srcmap)
+{
+	return get_iomap(inode, pos, length, iomap);
+}
+
+static const struct iomap_ops btrfs_dio_iomap_ops = {
+	.iomap_begin            = btrfs_dio_iomap_begin,
+};
+
+ssize_t btrfs_dio_iomap_read(struct kiocb *iocb, struct iov_iter *to)
+{
+	struct inode *inode = file_inode(iocb->ki_filp);
+	ssize_t ret;
+	inode_lock_shared(inode);
+	ret = iomap_dio_rw(iocb, to, &btrfs_dio_iomap_ops, NULL);
+	inode_unlock_shared(inode);
+	return ret;
+}
-- 
2.16.4