On Sat, Jun 29, 2019 at 03:30:20PM +0800, Chao Yu wrote:
> Some filesystems like erofs/reiserfs have the ability to pack tail
> data into metadata, however iomap framework can only support mapping
> inline data with IOMAP_INLINE type, it restricts that:
> - inline data should be locating at page #0.
> - inline size should equal to .i_size
Wouldn't it be easier simply to fix the meaning of IOMAP_INLINE so that
it can be used at something other than offset 0 and length == isize?
IOWs, make it mean "use the *inline_data pointer to read/write data
as a direct memory access"?
I also don't really like the idea of leaving the write paths
unimplemented in core code, though I suppose as an erofs developer
you're not likely to have a good means for testing... :/
/me starts wondering if a better solution would be to invent iomaptestfs
which exists solely to test all iomap code with as little other
intelligence as possible...
--D
> So we can not use IOMAP_INLINE to handle tail-packing case.
>
> This patch introduces new mapping type IOMAP_TAIL to map tail-packed
> data for further use of erofs.
>
> Signed-off-by: Chao Yu <yuchao0@xxxxxxxxxx>
> ---
> fs/iomap.c | 22 ++++++++++++++++++++++
> include/linux/iomap.h | 1 +
> 2 files changed, 23 insertions(+)
>
> diff --git a/fs/iomap.c b/fs/iomap.c
> index 12654c2e78f8..ae7777ce77d0 100644
> --- a/fs/iomap.c
> +++ b/fs/iomap.c
> @@ -280,6 +280,23 @@ iomap_read_inline_data(struct inode *inode, struct page *page,
> SetPageUptodate(page);
> }
>
> +static void
> +iomap_read_tail_data(struct inode *inode, struct page *page,
> + struct iomap *iomap)
> +{
> + size_t size = i_size_read(inode) & (PAGE_SIZE - 1);
> + void *addr;
> +
> + if (PageUptodate(page))
> + return;
> +
> + addr = kmap_atomic(page);
> + memcpy(addr, iomap->inline_data, size);
> + memset(addr + size, 0, PAGE_SIZE - size);
> + kunmap_atomic(addr);
> + SetPageUptodate(page);
> +}
> +
> static loff_t
> iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> struct iomap *iomap)
> @@ -298,6 +315,11 @@ iomap_readpage_actor(struct inode *inode, loff_t pos, loff_t length, void *data,
> return PAGE_SIZE;
> }
>
> + if (iomap->type == IOMAP_TAIL) {
> + iomap_read_tail_data(inode, page, iomap);
> + return PAGE_SIZE;
> + }
> +
> /* zero post-eof blocks as the page may be mapped */
> iomap_adjust_read_range(inode, iop, &pos, length, &poff, &plen);
> if (plen == 0)
> diff --git a/include/linux/iomap.h b/include/linux/iomap.h
> index 2103b94cb1bf..7e1ee48e3db7 100644
> --- a/include/linux/iomap.h
> +++ b/include/linux/iomap.h
> @@ -25,6 +25,7 @@ struct vm_fault;
> #define IOMAP_MAPPED 0x03 /* blocks allocated at @addr */
> #define IOMAP_UNWRITTEN 0x04 /* blocks allocated at @addr in unwritten state */
> #define IOMAP_INLINE 0x05 /* data inline in the inode */
> +#define IOMAP_TAIL 0x06 /* tail data packed in metdata */
>
> /*
> * Flags for all iomap mappings:
> --
> 2.18.0.rc1
>
