[PATCH v2] btrfs-progs: zoned: open host-managed devices with O_DIRECT for read-only

On host-managed zoned block devices the page cache cannot be used for
writing to the device because it does not guarantee ordering, therefore
direct I/O is used to write any on-disk data structures.

But reading in btrfs-progs is still performed using buffered I/O. This
mix of direct and buffered I/O can lead to stale page cache entries
being handed off to btrfs-progs and tools like "btrfs check" can report
spurious errors like:

	checksum verify failed on <bytenr> wanted 0x00000000 found 0xb6bde3e4

even though both copies are intact on disk.

Drop the O_RDWR condition so host-managed zoned devices always use
O_DIRECT, matching btrfstune.

Signed-off-by: Johannes Thumshirn <[email protected]>
---
Changes to v1:
- reworded commit message

 kernel-shared/disk-io.c | 2 +-
 kernel-shared/volumes.c | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel-shared/disk-io.c b/kernel-shared/disk-io.c
index 7f87e567f0b1..8b9c6dcac967 100644
--- a/kernel-shared/disk-io.c
+++ b/kernel-shared/disk-io.c
@@ -1722,7 +1722,7 @@ struct btrfs_fs_info *open_ctree_fs_info(struct open_ctree_args *oca)
 	if (!(oca->flags & OPEN_CTREE_WRITES))
 		oflags = O_RDONLY;

-	if ((oflags & O_RDWR) && zoned_model(oca->filename) == ZONED_HOST_MANAGED)
+	if (zoned_model(oca->filename) == ZONED_HOST_MANAGED)
 		oflags |= O_DIRECT;

 	fp = open(oca->filename, oflags);
diff --git a/kernel-shared/volumes.c b/kernel-shared/volumes.c
index f35b59bcc20e..e2b6708ad872 100644
--- a/kernel-shared/volumes.c
+++ b/kernel-shared/volumes.c
@@ -697,7 +697,7 @@ int btrfs_open_devices(struct btrfs_fs_info *fs_info,
 			continue;
 		}

-		if ((flags & O_RDWR) && zoned_model(device->name) == ZONED_HOST_MANAGED)
+		if (zoned_model(device->name) == ZONED_HOST_MANAGED)
 			flags |= O_DIRECT;

 		fd = open(device->name, flags);
--
2.54.0