[PATCH v3 4/4] ext4: support uncached buffered I/O

["陈涛涛 Taotao Chen" <chentaotao@didiglobal.com>]

From: Taotao Chen <chentaotao@didiglobal.com>

Set FOP_DONTCACHE in ext4_file_operations to declare support for
uncached buffered I/O.

To handle this flag, add processing for IOCB_DONTCACHE in
ext4_write_begin() and ext4_da_write_begin() by passing FGP_DONTCACHE
to page cache lookups.

Part of a series refactoring address_space_operations write_begin and
write_end callbacks to use struct kiocb for passing write context and
flags.

Signed-off-by: Taotao Chen <chentaotao@didiglobal.com>
---
 fs/ext4/file.c  | 3 ++-
 fs/ext4/inode.c | 6 ++++++
 2 files changed, 8 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/file.c b/fs/ext4/file.c
index 21df81347147..274b41a476c8 100644
--- a/fs/ext4/file.c
+++ b/fs/ext4/file.c
@@ -977,7 +977,8 @@ const struct file_operations ext4_file_operations = {
 	.splice_write	= iter_file_splice_write,
 	.fallocate	= ext4_fallocate,
 	.fop_flags	= FOP_MMAP_SYNC | FOP_BUFFER_RASYNC |
-			  FOP_DIO_PARALLEL_WRITE,
+			  FOP_DIO_PARALLEL_WRITE |
+			  FOP_DONTCACHE,
 };
 
 const struct inode_operations ext4_file_inode_operations = {
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index 08c10200d6fe..639e2e231c4b 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -1270,6 +1270,9 @@ static int ext4_write_begin(const struct kiocb *iocb,
 	if (unlikely(ret))
 		return ret;
 
+	if (iocb->ki_flags & IOCB_DONTCACHE)
+		fgp |= FGP_DONTCACHE;
+
 	trace_ext4_write_begin(inode, pos, len);
 	/*
 	 * Reserve one block more for addition to orphan list in case
@@ -3068,6 +3071,9 @@ static int ext4_da_write_begin(const struct kiocb *iocb,
 			return 0;
 	}
 
+	if (iocb->ki_flags & IOCB_DONTCACHE)
+		fgp |= FGP_DONTCACHE;
+
 retry:
 	fgp |= fgf_set_order(len);
 	folio = __filemap_get_folio(mapping, index, fgp,
-- 
2.34.1