On 4/17/19 9:34 AM, Darrick J. Wong wrote:
On Wed, Apr 18, 2019 at 09:27:11AM +0800, Shiyang Ruan wrote:
In XFS (under fsdax mode), reflink did not work correctly because xfs
iomap operators did not handle the inode with both reflink and dax flag.
This patchset aims to take care of this issue to make COW operation work
correctly in XFS.
XFS uses iomap to do read/write/mmap operations:
vfs interface xfs:
iomap_bengin(); --> xfs_iomap_begin();
actor(); --> dax_iomap_actor() / mmap actor function
iomap_end(); --> xfs_iomap_end();
In xfs_iomap_begin(), COW operation is detected but not told to actor
function. To resolve this, a new field 'src_addr' is added into
'struct iomap' to pass this COW info. It means the start address of
source blocks in a COW operation, for actor functions to copy data
before writing.
In actor functions, the value of iomap->src_addr determines if it is a
COW operation. If it is, copy data from source blocks to destination
blocks first, and then write user data.
After the COW operation, it is supposed to update the metadata of the
inode. Added in xfs_iomap_end().
How do the fs/iomap.c changes in your series compare with Goldwyn's
"btrfs dax support" series that he put out today?
Sorry, I think I missed his series. Will check it right now.
Also, there are a few things missing:
1. A DAX-compatible file contents comparison function for the dedupe
ioctl.
2. Checks that we aren't trying to reflink or dedupe between S_DAX and
!S_DAX files.
3. Do we need to make changes to the hairy
xfs_iolock_two_inodes_and_break_layout function to handle DAX? Seeing
as it doesn't call xfs_break_dax_layouts...
Thanks for your comments. I did not think carefully about 'dedupe'.
Will take this into consideration.
--
Thanks,
Shiyang Ruan.
--D
Shiyang Ruan (4):
fs/iomap: Introduce src_addr for COW in fsdax mode.
fs/xfs: iomap: add handle for reflink in fsdax mode
fs/dax: copy source blocks before writing when COW
fs/xfs: iomap: update the extent list after a COW
fs/dax.c | 70 +++++++++++++++++++++++++++++++++++++++++++
fs/xfs/xfs_iomap.c | 23 +++++++++++---
include/linux/iomap.h | 4 +++
3 files changed, 93 insertions(+), 4 deletions(-)
--
2.17.0
