Re: [PATCH 6/7] fs/xfs: Handle CoW for fsdax write() path

Christoph Hellwig
2021-02-08T15:24:38Z

> --- a/fs/xfs/xfs_bmap_util.c
> +++ b/fs/xfs/xfs_bmap_util.c
> @@ -977,10 +977,14 @@ xfs_free_file_space(
> if (offset + len > XFS_ISIZE(ip))
> len = XFS_ISIZE(ip) - offset;
> error = iomap_zero_range(VFS_I(ip), offset, len, NULL,
> - &xfs_buffered_write_iomap_ops);
> + IS_DAX(VFS_I(ip)) ?
> + &xfs_direct_write_iomap_ops : &xfs_buffered_write_iomap_ops);
> if (error)
> return error;
> + if (xfs_is_reflink_inode(ip))
> + xfs_reflink_end_cow(ip, offset, len);

Maybe we need to add (back) and xfs_zero_range helper that encapsulates
the details?

> trace_xfs_file_dax_write(ip, count, pos);
> ret = dax_iomap_rw(iocb, from, &xfs_direct_write_iomap_ops);
> - if (ret > 0 && iocb->ki_pos > i_size_read(inode)) {
> - i_size_write(inode, iocb->ki_pos);
> - error = xfs_setfilesize(ip, pos, ret);
> + if (ret > 0) {
> + if (iocb->ki_pos > i_size_read(inode)) {
> + i_size_write(inode, iocb->ki_pos);
> + error = xfs_setfilesize(ip, pos, ret);
> + }
> + if (xfs_is_cow_inode(ip))
> + xfs_reflink_end_cow(ip, pos, ret);

Nitpick, but I'd just goto out for ret <= 0 to reduce the indentation a
bit.

> }
> out:
> xfs_iunlock(ip, iolock);
> diff --git a/fs/xfs/xfs_iomap.c b/fs/xfs/xfs_iomap.c
> index 7b9ff824e82d..d6d4cc0f084e 100644
> --- a/fs/xfs/xfs_iomap.c
> +++ b/fs/xfs/xfs_iomap.c
> @@ -765,13 +765,14 @@ xfs_direct_write_iomap_begin(
> goto out_unlock;
>
> if (imap_needs_cow(ip, flags, &imap, nimaps)) {
> + bool need_convert = flags & IOMAP_DIRECT || IS_DAX(inode);
> error = -EAGAIN;
> if (flags & IOMAP_NOWAIT)
> goto out_unlock;
>
> /* may drop and re-acquire the ilock */
> error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
> - &lockmode, flags & IOMAP_DIRECT);
> + &lockmode, need_convert);

Why not:

error = xfs_reflink_allocate_cow(ip, &imap, &cmap, &shared,
&lockmode,
(flags & IOMAP_DIRECT) || IS_DAX(inode));

?