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Message-ID: <CAHc6FU5x3XOTyu8vooReSZ-hacfTdo3cu7wFJRcQrfTH8NkVeg@mail.gmail.com>
Date: Sun, 1 Aug 2021 14:03:33 +0200
From: Andreas Gruenbacher <agruenba@...hat.com>
To: Gao Xiang <hsiangkao@...ux.alibaba.com>
Cc: linux-erofs@...ts.ozlabs.org,
linux-fsdevel <linux-fsdevel@...r.kernel.org>,
LKML <linux-kernel@...r.kernel.org>,
Huang Jianan <huangjianan@...o.com>,
Joseph Qi <joseph.qi@...ux.alibaba.com>,
"Darrick J . Wong" <djwong@...nel.org>,
Christoph Hellwig <hch@....de>,
Matthew Wilcox <willy@...radead.org>
Subject: Re: [PATCH v9] iomap: Support file tail packing
On Tue, Jul 27, 2021 at 5:00 AM Gao Xiang <hsiangkao@...ux.alibaba.com> wrote:
> The existing inline data support only works for cases where the entire
> file is stored as inline data. For larger files, EROFS stores the
> initial blocks separately and then can pack a small tail adjacent to the
> inode. Generalise inline data to allow for tail packing. Tails may not
> cross a page boundary in memory.
>
> We currently have no filesystems that support tail packing and writing,
> so that case is currently disabled (see iomap_write_begin_inline).
>
> Cc: Darrick J. Wong <djwong@...nel.org>
> Reviewed-by: Christoph Hellwig <hch@....de>
> Reviewed-by: Matthew Wilcox (Oracle) <willy@...radead.org>
> Signed-off-by: Andreas Gruenbacher <agruenba@...hat.com>
> Signed-off-by: Gao Xiang <hsiangkao@...ux.alibaba.com>
> ---
> v8: https://lore.kernel.org/r/20210726145734.214295-1-hsiangkao@linux.alibaba.com
> changes since v8:
> - update the subject to 'iomap: Support file tail packing' as there
> are clearly a number of ways to make the inline data support more
> flexible (Matthew);
>
> - add one extra safety check (Darrick):
> if (WARN_ON_ONCE(size > iomap->length))
> return -EIO;
>
> fs/iomap/buffered-io.c | 42 ++++++++++++++++++++++++++++++------------
> fs/iomap/direct-io.c | 10 ++++++----
> include/linux/iomap.h | 18 ++++++++++++++++++
> 3 files changed, 54 insertions(+), 16 deletions(-)
>
> diff --git a/fs/iomap/buffered-io.c b/fs/iomap/buffered-io.c
> index 87ccb3438bec..f429b9d87dbe 100644
> --- a/fs/iomap/buffered-io.c
> +++ b/fs/iomap/buffered-io.c
> @@ -205,25 +205,32 @@ struct iomap_readpage_ctx {
> struct readahead_control *rac;
> };
>
> -static void
> -iomap_read_inline_data(struct inode *inode, struct page *page,
> +static int iomap_read_inline_data(struct inode *inode, struct page *page,
> struct iomap *iomap)
> {
> - size_t size = i_size_read(inode);
> + size_t size = i_size_read(inode) - iomap->offset;
> void *addr;
>
> if (PageUptodate(page))
> - return;
> + return 0;
>
> - BUG_ON(page_has_private(page));
> - BUG_ON(page->index);
> - BUG_ON(size > PAGE_SIZE - offset_in_page(iomap->inline_data));
> + /* inline data must start page aligned in the file */
> + if (WARN_ON_ONCE(offset_in_page(iomap->offset)))
> + return -EIO;
> + 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;
>
> addr = kmap_atomic(page);
> memcpy(addr, iomap->inline_data, size);
> memset(addr + size, 0, PAGE_SIZE - size);
> kunmap_atomic(addr);
> SetPageUptodate(page);
> + return 0;
> }
>
> static inline bool iomap_block_needs_zeroing(struct inode *inode,
> @@ -247,8 +254,10 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> sector_t sector;
>
> if (iomap->type == IOMAP_INLINE) {
> - WARN_ON_ONCE(pos);
> - iomap_read_inline_data(inode, page, iomap);
> + int ret = iomap_read_inline_data(inode, page, iomap);
> +
> + if (ret)
> + return ret;
> return PAGE_SIZE;
> }
>
> @@ -589,6 +598,15 @@ __iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, int flags,
> return 0;
> }
>
> +static int iomap_write_begin_inline(struct inode *inode,
> + struct page *page, struct iomap *srcmap)
> +{
> + /* needs more work for the tailpacking case, disable for now */
Nit: the comma should be a semicolon or period here.
> + if (WARN_ON_ONCE(srcmap->offset != 0))
> + return -EIO;
> + return iomap_read_inline_data(inode, page, srcmap);
> +}
> +
> static int
> iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
> struct page **pagep, struct iomap *iomap, struct iomap *srcmap)
> @@ -618,7 +636,7 @@ iomap_write_begin(struct inode *inode, loff_t pos, unsigned len, unsigned flags,
> }
>
> if (srcmap->type == IOMAP_INLINE)
> - iomap_read_inline_data(inode, page, srcmap);
> + status = iomap_write_begin_inline(inode, page, srcmap);
> else if (iomap->flags & IOMAP_F_BUFFER_HEAD)
> status = __block_write_begin_int(page, pos, len, NULL, srcmap);
> else
> @@ -671,11 +689,11 @@ static size_t iomap_write_end_inline(struct inode *inode, struct page *page,
> void *addr;
>
> WARN_ON_ONCE(!PageUptodate(page));
> - BUG_ON(pos + copied > PAGE_SIZE - offset_in_page(iomap->inline_data));
> + BUG_ON(!iomap_inline_data_valid(iomap));
>
> flush_dcache_page(page);
> addr = kmap_atomic(page);
> - memcpy(iomap->inline_data + pos, addr + pos, copied);
> + memcpy(iomap_inline_data(iomap, pos), addr + pos, copied);
> kunmap_atomic(addr);
>
> mark_inode_dirty(inode);
> diff --git a/fs/iomap/direct-io.c b/fs/iomap/direct-io.c
> index 9398b8c31323..41ccbfc9dc82 100644
> --- a/fs/iomap/direct-io.c
> +++ b/fs/iomap/direct-io.c
> @@ -378,23 +378,25 @@ iomap_dio_inline_actor(struct inode *inode, loff_t pos, loff_t length,
> struct iomap_dio *dio, struct iomap *iomap)
> {
> struct iov_iter *iter = dio->submit.iter;
> + void *inline_data = iomap_inline_data(iomap, pos);
> size_t copied;
>
> - BUG_ON(pos + length > PAGE_SIZE - offset_in_page(iomap->inline_data));
> + if (WARN_ON_ONCE(!iomap_inline_data_valid(iomap)))
> + return -EIO;
>
> if (dio->flags & IOMAP_DIO_WRITE) {
> loff_t size = inode->i_size;
>
> if (pos > size)
> - memset(iomap->inline_data + size, 0, pos - size);
> - copied = copy_from_iter(iomap->inline_data + pos, length, iter);
> + memset(iomap_inline_data(iomap, size), 0, pos - size);
> + copied = copy_from_iter(inline_data, length, iter);
> if (copied) {
> if (pos + copied > size)
> i_size_write(inode, pos + copied);
> mark_inode_dirty(inode);
> }
> } else {
> - copied = copy_to_iter(iomap->inline_data + pos, length, iter);
> + copied = copy_to_iter(inline_data, length, iter);
> }
> dio->size += copied;
> return copied;
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 479c1da3e221..b8ec145b2975 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -97,6 +97,24 @@ iomap_sector(struct iomap *iomap, loff_t pos)
> return (iomap->addr + pos - iomap->offset) >> SECTOR_SHIFT;
> }
>
> +/*
> + * Returns the inline data pointer for logical offset @pos.
> + */
> +static inline void *iomap_inline_data(struct iomap *iomap, loff_t pos)
> +{
> + return iomap->inline_data + pos - iomap->offset;
> +}
> +
> +/*
> + * Check if the mapping's length is within the valid range for inline data.
> + * This is used to guard against accessing data beyond the page inline_data
> + * points at.
> + */
> +static inline bool iomap_inline_data_valid(struct iomap *iomap)
> +{
> + return iomap->length <= PAGE_SIZE - offset_in_page(iomap->inline_data);
> +}
> +
> /*
> * When a filesystem sets page_ops in an iomap mapping it returns, page_prepare
> * and page_done will be called for each page written to. This only applies to
> --
> 2.24.4
>
Andreas
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