Am Mo., 1. Juli 2019 um 10:04 Uhr schrieb Gao Xiang <gaoxiang25@xxxxxxxxxx>:
> On 2019/7/1 14:40, Chao Yu wrote:
> > Hi Xiang,
> >
> > On 2019/6/29 17:34, Gao Xiang wrote:
> >> Hi Chao,
> >>
> >> On 2019/6/29 15:30, 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
> >>> 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);
> >>
> >> need flush_dcache_page(page) here for new page cache page since
> >> it's generic iomap code (althrough not necessary for x86, arm), I am not sure...
> >> see commit d2b2c6dd227b and c01778001a4f...
> >
> > Thanks for your reminding, these all codes were copied from
> > iomap_read_inline_data(), so I think we need a separated patch to fix this issue
> > if necessary.
>
> Yes, just a reminder, it is good as it-is.
Not sure if that means that IOMAP_INLINE as is works for you now. In
any case, if the inline data isn't transparently copied into the page
cache at index 0, memory-mapped I/O isn't going to work.
The code further assumes that "packed" files consist of exactly one
IOMAP_INLINE mapping; no IOMAP_MAPPED or other mappings may follow. Is
it that assumption that's causing you trouble? If so, what's the
layout at the filesystem level you want to support?
Thanks,
Andreas
> Thanks,
> Gao Xiang
>
> >
> > Thanks,
> >
> >>
> >> Thanks,
> >> Gao Xiang
> >>
> >>> + 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:
> >>>
> >> .
> >>
