Re: [Ocfs2-devel] [PATCH v2 09/10] fs/xfs: Handle CoW for fsdax write() path

["ruansy.fnst@fujitsu.com" <ruansy.fnst@fujitsu.com>]

> 
> On Fri, Feb 26, 2021 at 08:20:29AM +0800, Shiyang Ruan wrote:
> >       error = iomap_zero_range(VFS_I(ip), offset, len, NULL,
> > -                     &xfs_buffered_write_iomap_ops);
> > +               IS_DAX(VFS_I(ip)) ?
> > +               &xfs_dax_write_iomap_ops : &xfs_buffered_write_iomap_ops);
> 
> Please add a xfs_zero_range helper that picks the right iomap_ops
> instead of open coding this in a few places.

OK.  I'll add it.
> 
> > +static int
> > +xfs_dax_write_iomap_end(
> > +     struct inode            *inode,
> > +     loff_t                  pos,
> > +     loff_t                  length,
> > +     ssize_t                 written,
> > +     unsigned int            flags,
> > +     struct iomap            *iomap)
> > +{
> > +     int                     error = 0;
> > +     xfs_inode_t             *ip = XFS_I(inode);
> > +
> > +     if (pos + written > i_size_read(inode)) {
> > +             i_size_write(inode, pos + written);
> > +             error = xfs_setfilesize(ip, pos, written);
> > +     }
> > +     if (xfs_is_cow_inode(ip))
> > +             error = xfs_reflink_end_cow(ip, pos, written);
> > +
> > +     return error;
> 
> What is the advantage of the ioemap_end handler here?  It adds another
> indirect funtion call to the fast path, so if we can avoid it, I'd
> rather do that.

These code were in xfs_file_dax_write().  I moved them into the iomap_end
because the mmaped CoW need this.

I know this is not so good, but I could not find another better way. Do you
have any ideas? 

>
> Also, shouldn't we cancel the COW rather than finishing it when setting
> the file size fails?
> 

I did forget about this part.  Thanks for pointing out.


--
Thanks,
Ruan Shiyang.
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