ext4: introduce direct I/O read using iomap infrastructure

This patch introduces a new direct I/O read path which makes use of
the iomap infrastructure.

The new function ext4_do_read_iter() is responsible for calling into
the iomap infrastructure via iomap_dio_rw(). If the read operation
performed on the inode is not supported, which is checked via
ext4_dio_supported(), then we simply fallback and complete the I/O
using buffered I/O.

Existing direct I/O read code path has been removed, as it is now
redundant.

Signed-off-by: Matthew Bobrowski <mbobrowski@mbobrowski.org>
Reviewed-by: Jan Kara <jack@suse.cz>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/f98a6f73fadddbfbad0fc5ed04f712ca0b799f37.1572949325.git.mbobrowski@mbobrowski.org
Signed-off-by: Theodore Ts'o <tytso@mit.edu>

1 files changed, 1 insertions, 37 deletions

diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index b5ba6767b276..9bd80df6b856 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -863,9 +863,6 @@ int ext4_dio_get_block(struct inode *inode, sector_t iblock,
 {
 	/* We don't expect handle for direct IO */
 	WARN_ON_ONCE(ext4_journal_current_handle());
-
-	if (!create)
-		return _ext4_get_block(inode, iblock, bh, 0);
 	return ext4_get_block_trans(inode, iblock, bh, EXT4_GET_BLOCKS_CREATE);
 }
 
@@ -3916,36 +3913,6 @@ out:
 	return ret;
 }
 
-static ssize_t ext4_direct_IO_read(struct kiocb *iocb, struct iov_iter *iter)
-{
-	struct address_space *mapping = iocb->ki_filp->f_mapping;
-	struct inode *inode = mapping->host;
-	size_t count = iov_iter_count(iter);
-	ssize_t ret;
-
-	/*
-	 * Shared inode_lock is enough for us - it protects against concurrent
-	 * writes & truncates and since we take care of writing back page cache,
-	 * we are protected against page writeback as well.
-	 */
-	if (iocb->ki_flags & IOCB_NOWAIT) {
-		if (!inode_trylock_shared(inode))
-			return -EAGAIN;
-	} else {
-		inode_lock_shared(inode);
-	}
-
-	ret = filemap_write_and_wait_range(mapping, iocb->ki_pos,
-					   iocb->ki_pos + count - 1);
-	if (ret)
-		goto out_unlock;
-	ret = __blockdev_direct_IO(iocb, inode, inode->i_sb->s_bdev,
-				   iter, ext4_dio_get_block, NULL, NULL, 0);
-out_unlock:
-	inode_unlock_shared(inode);
-	return ret;
-}
-
 static ssize_t ext4_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 {
 	struct file *file = iocb->ki_filp;
@@ -3972,10 +3939,7 @@ static ssize_t ext4_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
 		return 0;
 
 	trace_ext4_direct_IO_enter(inode, offset, count, iov_iter_rw(iter));
-	if (iov_iter_rw(iter) == READ)
-		ret = ext4_direct_IO_read(iocb, iter);
-	else
-		ret = ext4_direct_IO_write(iocb, iter);
+	ret = ext4_direct_IO_write(iocb, iter);
 	trace_ext4_direct_IO_exit(inode, offset, count, iov_iter_rw(iter), ret);
 	return ret;
 }