Re: [PATCH] erofs: use the shared page cache for splice in inode_share mode

[Zhan Xusheng <zhanxusheng1024@gmail.com>]

On Thu, 20 Aug 2026 17:53:20 +0800, Jingbo Xu wrote:
> Please refer to backing_file_splice_read() called from
> ovl_splice_read(), file_accessed() needs to be called on the original
> file (just as what .read_iter() i.e. filemap_read() does), and the input
> @ppos needs to be updated accordingly.

Taking the file_accessed() one, thanks.  filemap_splice_read() calls it at
mm/filemap.c:3155 on whatever file it was handed, so on the backing file,
whereas backing_file_splice_read() ends in ctx->accessed(iocb->ki_filp),
which for ovl_splice_read() is the original.  v2 adds file_accessed(in).

@ppos looks already handled to me.  filemap_splice_read() takes a loff_t *
and advances it itself, at mm/filemap.c:3144; its internal kiocb is seeded
from *ppos at 3083 and 3098, not the other way round.  ovl_splice_read()
has to copy iocb.ki_pos back because backing_file_splice_read() takes a
struct kiocb and hands &iocb->ki_pos to vfs_splice_read().  Say if I have
that wrong.

One you may want for read_iter too: it clones the kiocb onto the backing
file, so filemap_read() marks that one accessed rather than the user's
file, which is the shape splice_read had.  Neither is observable today,
since erofs_fc_fill_super() sets SB_RDONLY | SB_NOATIME and the backing
file is opened O_NOATIME, so both reach a no-op.  That is why I left
read_iter alone here.

Thanks,
Zhan Xusheng