On Wed, Mar 01, 2006 at 05:51:48PM -0800, Andrew Morton wrote:
> Badari Pulavarty <[email protected]> wrote:
> >
> > + * Historically, a buffer_head was used to map a single block
> > + * within a page, and of course as the unit of I/O through the
> > + * filesystem and block layers. Nowadays the basic I/O unit
> > + * is the bio, and buffer_heads are used for extracting block
> > + * mappings (via a get_block_t call), for tracking state within
> > + * a page (via a page_mapping) and for wrapping bio submission
> > + * for backward compatibility reasons (e.g. submit_bh).
>
> Well kinda. A buffer_head remains the kernel's basic abstraction for a
> "disk block".
Thats what I said (meant to say) with
"buffer_heads are used for extracting block mappings".
I think by "disk block" you mean what I'm thinking of as a
"block mapping" (series of contiguous blocks). I'd think
of a sector_t as a "disk block", but maybe I'm just wierd
that way... a better wordsmith should jump in and update
the comment I guess.
> We cannot replace that with `struct page' (size isn't
> flexible) nor of course with `struct bio'.
Indeed.
--
Nathan
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