12:06 p.m.
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
>
>
>