On Tue, Oct 04, 2011 at 10:43:05AM +1100, Dave Chinner wrote:
> The lookup is pretty simple - if there's cached data over the
> unwritten range, then I'm considering it a data range. If there's no
> cached data over the unwritten extent, it's a hole. That makes the
> lookup simply a case of finding the first cached page in the
> unwritten extent.
>
> It'll end up reading something like this:
>
> iomap = offset_to_extent(offset);
> first_index = extent_to_page_index(iomap);
>
> nr_found = pagevec_lookup(&pvec, inode->i_mapping, first_index, 1);
> if (!nr_found)
> break;
>
> offset = page->index << PAGECACHE_SHIFT;
> pagevec_release(&pvec);
>
> /* If we fell off the end of the extent lookup next extent */
> if (offset >= end_of_extent(iomap)) {
> offset = end_of_extent(iomap);
> goto next_extent;
> }
>
> All the extent manipulations are pretty filesystem specific, so
> there's not much that can be extracted into generic helper, I
> think...
Actually pretty similar code will work just fine if you passt the
start + len of the extents in (which we got from looking it up
fs-specificly):
Note that we have to look for both dirty and writeback pages to
make it safe.
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