Re: [PATCH v2] iomap: Support inline data with block size < page size

[Andreas Gruenbacher <agruenba@redhat.com>]

On Thu, Jul 29, 2021 at 5:25 AM Matthew Wilcox (Oracle)
<willy@infradead.org> wrote:
> Remove the restriction that inline data must start on a page boundary
> in a file.  This allows, for example, the first 2KiB to be stored out
> of line and the trailing 30 bytes to be stored inline.
>
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> ---
> v2:
>  - Rebase on top of iomap: Support file tail packing v9
>
>  fs/iomap/buffered-io.c | 34 ++++++++++++++++------------------
>  1 file changed, 16 insertions(+), 18 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 66b733537c46..50f18985ed13 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -209,28 +209,26 @@ static int iomap_read_inline_data(struct inode *inode, struct page *page,
>                 struct iomap *iomap)
>  {
>         size_t size = i_size_read(inode) - iomap->offset;
> +       size_t poff = offset_in_page(iomap->offset);
>         void *addr;
>
>         if (PageUptodate(page))
> -               return 0;
> +               return PAGE_SIZE - poff;
>
> -       /* inline data must start page aligned in the file */
> -       if (WARN_ON_ONCE(offset_in_page(iomap->offset)))
> -               return -EIO;

Maybe add a WARN_ON_ONCE(size > PAGE_SIZE - poff) here?

>         if (WARN_ON_ONCE(size > PAGE_SIZE -
>                          offset_in_page(iomap->inline_data)))
>                 return -EIO;
>         if (WARN_ON_ONCE(size > iomap->length))
>                 return -EIO;
> -       if (WARN_ON_ONCE(page_has_private(page)))
> -               return -EIO;
> +       if (poff > 0)
> +               iomap_page_create(inode, page);
>
> -       addr = kmap_atomic(page);
> +       addr = kmap_atomic(page) + poff;

Maybe kmap_local_page?

>         memcpy(addr, iomap->inline_data, size);
> -       memset(addr + size, 0, PAGE_SIZE - size);
> +       memset(addr + size, 0, PAGE_SIZE - poff - size);
>         kunmap_atomic(addr);
> -       SetPageUptodate(page);
> -       return 0;
> +       iomap_set_range_uptodate(page, poff, PAGE_SIZE - poff);
> +       return PAGE_SIZE - poff;
>  }
>
>  static inline bool iomap_block_needs_zeroing(struct inode *inode,
> @@ -252,13 +250,8 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
>         unsigned poff, plen;
>         sector_t sector;
>
> -       if (iomap->type == IOMAP_INLINE) {
> -               int ret = iomap_read_inline_data(inode, page, iomap);
> -
> -               if (ret)
> -                       return ret;
> -               return PAGE_SIZE;
> -       }
> +       if (iomap->type == IOMAP_INLINE)
> +               return iomap_read_inline_data(inode, page, iomap);
>
>         /* zero post-eof blocks as the page may be mapped */
>         iop = iomap_page_create(inode, page);
> @@ -593,10 +586,15 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
>  static int iomap_write_begin_inline(struct inode *inode,
>                 struct page *page, struct iomap *srcmap)
>  {
> +       int ret;
> +
>         /* needs more work for the tailpacking case, disable for now */
>         if (WARN_ON_ONCE(srcmap->offset != 0))
>                 return -EIO;
> -       return iomap_read_inline_data(inode, page, srcmap);
> +       ret = iomap_read_inline_data(inode, page, srcmap);
> +       if (ret < 0)
> +               return ret;
> +       return 0;
>  }
>
>  static int
> --
> 2.30.2
>

Thanks,
Andreas