[PATCH] erofs: support direct IO for uncompressed file

[Huang Jianan <huangjianan@oppo.com>]

direct IO is useful in certain scenarios for uncompressed files.
For example, it can avoid double pagecache when use the uncompressed
file to mount upper layer filesystem.

In addition, another patch adds direct IO test for the stress tool
which was mentioned here:
https://lore.kernel.org/linux-erofs/20200206135631.1491-1-hsiangkao@aol.com/

Signed-off-by: Huang Jianan <huangjianan@oppo.com>
Signed-off-by: Guo Weichao <guoweichao@oppo.com>
---
 fs/erofs/data.c | 57 +++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 57 insertions(+)

diff --git a/fs/erofs/data.c b/fs/erofs/data.c
index ea4f693bee22..3067aa3defff 100644
--- a/fs/erofs/data.c
+++ b/fs/erofs/data.c
@@ -6,6 +6,8 @@
  */
 #include "internal.h"
 #include <linux/prefetch.h>
+#include <linux/uio.h>
+#include <linux/blkdev.h>
 
 #include <trace/events/erofs.h>
 
@@ -312,6 +314,60 @@ static void erofs_raw_access_readahead(struct readahead_control *rac)
 		submit_bio(bio);
 }
 
+static int erofs_get_block(struct inode *inode, sector_t iblock,
+			   struct buffer_head *bh, int create)
+{
+	struct erofs_map_blocks map = {
+		.m_la = blknr_to_addr(iblock),
+	};
+	int err;
+
+	err = erofs_map_blocks(inode, &map, EROFS_GET_BLOCKS_RAW);
+	if (err)
+		return err;
+
+	if (map.m_flags & EROFS_MAP_MAPPED)
+		map_bh(bh, inode->i_sb, erofs_blknr(map.m_pa));
+
+	return err;
+}
+
+static int check_direct_IO(struct inode *inode, struct iov_iter *iter,
+			   loff_t offset)
+{
+	unsigned i_blkbits = READ_ONCE(inode->i_blkbits);
+	unsigned blkbits = i_blkbits;
+	unsigned blocksize_mask = (1 << blkbits) - 1;
+	unsigned long align = offset | iov_iter_alignment(iter);
+	struct block_device *bdev = inode->i_sb->s_bdev;
+
+	if (align & blocksize_mask) {
+		if (bdev)
+			blkbits = blksize_bits(bdev_logical_block_size(bdev));
+		blocksize_mask = (1 << blkbits) - 1;
+		if (align & blocksize_mask)
+			return -EINVAL;
+		return 1;
+	}
+	return 0;
+}
+
+static ssize_t erofs_direct_IO(struct kiocb *iocb, struct iov_iter *iter)
+{
+	struct address_space *mapping = iocb->ki_filp->f_mapping;
+	struct inode *inode = mapping->host;
+	loff_t offset = iocb->ki_pos;
+	int err;
+
+	err = check_direct_IO(inode, iter, offset);
+	if (err)
+		return err < 0 ? err : 0;
+
+	return __blockdev_direct_IO(iocb, inode, inode->i_sb->s_bdev, iter,
+				    erofs_get_block, NULL, NULL,
+				    DIO_LOCKING | DIO_SKIP_HOLES);
+}
+
 static sector_t erofs_bmap(struct address_space *mapping, sector_t block)
 {
 	struct inode *inode = mapping->host;
@@ -336,6 +392,7 @@ static sector_t erofs_bmap(struct address_space *mapping, sector_t block)
 const struct address_space_operations erofs_raw_access_aops = {
 	.readpage = erofs_raw_access_readpage,
 	.readahead = erofs_raw_access_readahead,
+	.direct_IO = erofs_direct_IO,
 	.bmap = erofs_bmap,
 };
 
-- 
2.25.1