Re: VFS interactions with UML and other big UML changes (was: Re: [patch 1/2] Uml - first part rework of run_helper() and users.)

[Andrew Morton <akpm@osdl.org>]

Blaisorblade <blaisorblade_spam@yahoo.it> wrote:
>
> static struct address_space_operations hostfs_aops = {
>         .writepage      = hostfs_writepage,
>         .readpage       = hostfs_readpage,
> /*      .set_page_dirty = __set_page_dirty_nobuffers, */
>         .prepare_write  = hostfs_prepare_write,
>         .commit_write   = hostfs_commit_write
> };
> 
> Actually, hostfs is a nodev filesystem, but I simply don't know if that 
> implies that it uses no buffers. So, should
> 
>  .set_page_dirty = __set_page_dirty_nobuffers
> 
> be uncommented? Or should it be deleted (leaving it there is not a good 
> option).

See the operation of set_page_dirty().

If you have NULL ->set_page_dirty a_op then set_page_dirty() will fall
through to __set_page_dirty_buffers().

If your fs never sets PG_private then __set_page_dirty_buffers() will just
do what __set_page_dirty_nobuffers() does.

Without having looked at it, I'm sure that hostfs does not use
buffer_heads.  So setting your ->set_page_dirty a_op to point at
__set_page_dirty_nobuffers() is a reasonable thing to do - it'll provide a
slight speedup.