Re: [PATCH 1/2] BDI: Provide backing device capability information

[Andrew Morton <akpm@osdl.org>]

David Howells <dhowells@redhat.com> wrote:
>
> 
> The attached patch does two things:
> 
>  (1) It gets rid of backing_dev_info::memory_backed and replaces it with a
>      pair of boolean values:
> 
> 	(*) dirty_memory_acct
> 
> 	    True if the pages associated with this backing device should be
> 	    tracked by dirty page accounting.
> 
>         (*) writeback_if_dirty
> 
> 	    True if the pages associated with this backing device should have
> 	    writepage() or writepages() invoked upon them to clean them.

Cool, thanks.

>  (2) It adds a backing device capability mask that indicates what a backing
>      device is capable of; currently only in regard to memory mapping
>      facilities. These flags indicate whether a device can be mapped directly,
>      whether it can be copied for a mapping, and whether direct mappings can
>      be read, written and/or executed. This information is primarily aimed at
>      improving no-MMU private mapping support.
> 
> ...

> +#define BDI_CAP_MAP_COPY	0x00000001	/* Copy can be mapped (MAP_PRIVATE) */
> +#define BDI_CAP_MAP_DIRECT	0x00000002	/* Can be mapped directly (MAP_SHARED) */

Why not make these bitfields as well?