Re: [PATCH v2 06/11] xfs: Reflink CoW-based atomic write support

John Garry
2025-02-25T10:59:53Z

On 24/02/2025 20:32, Darrick J. Wong wrote:
> On Thu, Feb 13, 2025 at 01:56:14PM +0000, John Garry wrote:
>> For CoW-based atomic write support, always allocate a cow hole in
>> xfs_reflink_allocate_cow() to write the new data.
>>
>> The semantics is that if @atomic is set, we will be passed a CoW fork
>> extent mapping for no error returned.
>>
>> Signed-off-by: John Garry <john.g.garry@oracle.com>
>> ---
>> fs/xfs/xfs_iomap.c | 2 +-
>> fs/xfs/xfs_reflink.c | 12 +++++++-----
>> fs/xfs/xfs_reflink.h | 2 +-
>> 3 files changed, 9 insertions(+), 7 deletions(-)
>>
>> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
>> index d61460309a78..ab79f0080288 100644
>> --- a/fs/xfs/xfs_iomap.c
>> +++ b/fs/xfs/xfs_iomap.c
>> @@ -865,7 +865,7 @@ xfs_direct_write_iomap_begin(
>> /* may drop and re-acquire the ilock */
>> error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
>> &lockmode,
>> - (flags & IOMAP_DIRECT) || IS_DAX(inode));
>> + (flags & IOMAP_DIRECT) || IS_DAX(inode), false);
>
> Now I'm /really/ think it's time for some reflink allocation flags,
> because the function signature now involves two booleans...

ok, but the @convert_now arg is passed to other functions from
xfs_reflink_allocate_cow() - so would you prefer to create a bool
@convert_now inside xfs_reflink_allocate_cow() and pass that bool as
before? Or pass the flags all the way down to end users of @convert_now?

>
>> if (error)
>> goto out_unlock;
>> if (shared)
>> diff --git a/fs/xfs/xfs_reflink.c b/fs/xfs/xfs_reflink.c
>> index 8428f7b26ee6..3dab3ba900a3 100644
>> --- a/fs/xfs/xfs_reflink.c
>> +++ b/fs/xfs/xfs_reflink.c
>> @@ -435,7 +435,8 @@ xfs_reflink_fill_cow_hole(
>> struct xfs_bmbt_irec *cmap,
>> bool *shared,
>> uint *lockmode,
>> - bool convert_now)
>> + bool convert_now,
>> + bool atomic)
>
> ...but this can come later.

Do you mean that this would just be a new flag to set?

> Also, is atomic==true only for the> ATOMIC_SW operation?

Right, so I think that the variable (or new flag) can be renamed for that.

> I think so, but that's the unfortunate thing about
> booleans.
>
>> {
>> struct xfs_mount *mp = ip->i_mount;
>> struct xfs_trans *tp;
>> @@ -466,7 +467,7 @@ xfs_reflink_fill_cow_hole(
>> *lockmode = XFS_ILOCK_EXCL;
>>
>> error = xfs_find_trim_cow_extent(ip, imap, cmap, shared, &found);
>> - if (error || !*shared)
>> + if (error || (!*shared && !atomic))
>> goto out_trans_cancel;
>>
>> if (found) {
>> @@ -566,7 +567,8 @@ xfs_reflink_allocate_cow(
>> struct xfs_bmbt_irec *cmap,
>> bool *shared,
>> uint *lockmode,
>> - bool convert_now)
>> + bool convert_now,
>> + bool atomic)
>
> Nit: ^ space before tab.

ok

>
> If the answer to the question above is 'yes' then with that nit fixed,
> Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>

Thanks, but I will wait for your feedback to decide whether to pick that up.

John