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SubjectRe: [PATCH 1/2] iomap: support tail packing inline read
On Fri, Jul 16, 2021 at 10:19:09AM +0100, Christoph Hellwig wrote:
> static void
> iomap_read_inline_data(struct inode *inode, struct page *page,
> - struct iomap *iomap)
> + struct iomap *iomap, loff_t pos, unsigned int size)
> {
> - size_t size = i_size_read(inode);
> + unsigned int block_aligned_size = round_up(size, i_blocksize(inode));
> + unsigned int poff = offset_in_page(pos);
> void *addr;
>
> - if (PageUptodate(page))
> - return;
> -
> - BUG_ON(page_has_private(page));
> - BUG_ON(page->index);
> + /* make sure that inline_data doesn't cross page boundary */
> BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
> + BUG_ON(size != i_size_read(inode) - pos);
>
> addr = kmap_atomic(page);
> - memcpy(addr, iomap->inline_data, size);
> - memset(addr + size, 0, PAGE_SIZE - size);
> + memcpy(addr + poff, iomap->inline_data - iomap->offset + pos, size);
> + memset(addr + poff + size, 0, block_aligned_size - size);
> kunmap_atomic(addr);
> - SetPageUptodate(page);
> +
> + iomap_set_range_uptodate(page, poff, block_aligned_size);
> }

This should be relatively straightforward to port to folios.
I think it looks something like this ...

@@ -211,23 +211,18 @@ struct iomap_readpage_ctx {
};

static void iomap_read_inline_data(struct inode *inode, struct folio *folio,
- struct iomap *iomap)
+ struct iomap *iomap, loff_t pos, size_t size)
{
- size_t size = i_size_read(inode);
void *addr;
+ size_t offset = offset_in_folio(folio, pos);

- if (folio_test_uptodate(folio))
- return;
+ BUG_ON(size != i_size_read(inode) - pos);

- BUG_ON(folio->index);
- BUG_ON(folio_multi(folio));
- BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
-
- addr = kmap_local_folio(folio, 0);
+ addr = kmap_local_folio(folio, offset);
memcpy(addr, iomap->inline_data, size);
memset(addr + size, 0, PAGE_SIZE - size);
kunmap_local(addr);
- folio_mark_uptodate(folio);
+ iomap_set_range_uptodate(folio, to_iomap_page(folio), pos, size);
}

> - if (iomap->type == IOMAP_INLINE) {
> - WARN_ON_ONCE(pos);
> - iomap_read_inline_data(inode, page, iomap);
> - return PAGE_SIZE;
> - }
> + if (iomap->type == IOMAP_INLINE && !pos)
> + WARN_ON_ONCE(to_iomap_page(page) != NULL);
> + else
> + iop = iomap_page_create(inode, page);

This WARN_ON doesn't make sense to me. If a file contains bytes 0-2047
that are !INLINE and then bytes 2048-2050 that are INLINE, we're going
to trigger it. Perhaps just make this:
if (iomap->type != IOMAP_INLINE || pos)
iop = iomap_page_create(inode, page);
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