On Tue, 1 May 2007, Nate Diller wrote:
> well, leave it to me to reply too quickly, sorry. i think we should
> leave simple_prepare_write() the way it is, since it's a library
> function itself. the other two callsites in your patch are buffers,
> which may themselves be smaller than a page so you would need a
> special function for just those two uses, there's no other way to
> avoid making two calls to flush_dcache_page(). if it's tremendously
> important to you to eliminate open coding of these, maybe make a
> 'static int buffer_prepare_write()' or some such in fs/buffer.c
All three sites zap two parts of a page. If we had a
zero_user_page2 like this
zero_user_page2(page, start1, end1, start2, end2, kmap)
then all 3 sites could use the same funtion.
libfs.c:
zero_user_page_segments(page, 0, from, to, PAGE_CACHE_SIZE, KM_USER0);
buffer.c:
zero_user_page_segments(page, from, block_start, to, block_end, KM_USER0)
zero_user_page_segments(page, blockstart, from, to, block_end, KM_USER0)
I did not look through the whole kernel but this zapping segments is
likely frequent given the nature of the blocklayer.
The 3 call sites pretty ugly on their own. I think it would be good
to have one clearly commented version of this somewhere. Call sites
will be much clearer since you do not have the kmap_ obfuscation nor
the calculation of the length of each segment.
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