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

[Goldwyn Rodrigues]

From: Goldwyn Rodrigues <rgold...@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 <rgold...@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