Re: [PATCH v2 07/11] xfs: iomap CoW-based atomic write support

John Garry
2025-02-25T18:07:27Z

On 25/02/2025 17:47, Darrick J. Wong wrote:
>> I can try, and would then need to try to factor out what would be much
>> duplicated code.
> <nod> I think it's pretty straightforward:

Yeah, I already had done sometime like this since.

>
> xfs_direct_cow_write_iomap_begin()
> {
> ASSERT(flags & IOMAP_WRITE);
> ASSERT(flags & IOMAP_DIRECT);
> ASSERT(flags & IOMAP_ATOMIC_SW);
>
> if (xfs_is_shutdown(mp))
> return -EIO;
>
> /*
> * Writes that span EOF might trigger an IO size update on
> * completion, so consider them to be dirty for the purposes of
> * O_DSYNC even if there is no other metadata changes pending or
> * have been made here.
> */
> if (offset + length > i_size_read(inode))
> iomap_flags |= IOMAP_F_DIRTY;
>
> lockmode = XFS_ILOCK_EXCL;
> error = xfs_ilock_for_iomap(ip, flags, &lockmode);
> if (error)
> return error;
>
> error = xfs_bmapi_read(ip, offset_fsb, end_fsb - offset_fsb,
> &imap, &nimaps, 0);
> if (error)
> goto out_unlock;
>
> error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
> &lockmode, true, true);
> if (error)
> goto out_unlock;
>
> endoff = XFS_FSB_TO_B(mp, cmap.br_startoff + cmap.br_blockcount);
> trace_xfs_iomap_found(ip, offset, endoff - offset, XFS_COW_FORK,
> &cmap);
> if (imap.br_startblock != HOLESTARTBLOCK) {

note: As you know, all this is common to xfs_direct_write_iomap_begin(),
but unfortunately can't neatly be factored out due to the xfs_iunlock()
calls.

> seq = xfs_iomap_inode_sequence(ip, 0);
> error = xfs_bmbt_to_iomap(ip, srcmap, &imap, flags, 0,
> seq);
> if (error)
> goto out_unlock;
> }
> seq = xfs_iomap_inode_sequence(ip, IOMAP_F_SHARED);
> xfs_iunlock(ip, lockmode);
> return xfs_bmbt_to_iomap(ip, iomap, &cmap, flags,
> IOMAP_F_SHARED, seq);
>
> out_unlock:
> if (lockmode)
> xfs_iunlock(ip, lockmode);
> return error;
> }

Cheers,
John