Matthew Wilcox <willy@xxxxxxxxxxxxx> wrote:
> Anyway, looking at netfs_write_begin(), it's wrong too, in a bunch of
> ways. You don't need to zero out the part of the page you're going to
> copy into.
Zeroing it out isn't 'wrong', per se, just inefficient. Fixing that needs the
filesystem to deal with it if the copy fails.
> And the condition is overly complicated which makes it
> hard to know what's going on. Setting aside the is_cache_enabled part,
> I think you want:
>
> if (offset == 0 && len >= thp_size(page))
> goto have_page_no_wait;
> if (page_offset(page) >= size) {
> zero_user_segments(page, 0, offset,
> offset + len, thp_size(page));
There's a third case too: where the write starts at the beginning of the page
and goes to/straddles the EOF - but doesn't continue to the end of the page.
You also didn't set PG_uptodate - presumably deliberately because there's a
hole potentially containing random rubbish in the middle.
> goto have_page_no_wait;
> }
> ... read the interesting chunks of page ...
David
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