Re: [PATCH] erofs: support SEEK_HOLE/SEEK_DATA in inode_share mode

[Zhan Xusheng <zhanxusheng1024@gmail.com>]

On Tue, 18 Aug 2026 19:37:13 +0800, Jingbo Xu wrote:
> - .llseek   = generic_file_llseek,
> + .llseek   = erofs_file_llseek,

No objection to the change.  While in that table, .splice_read is the entry
left that touches the page cache without going through ->private_data:

  .read_iter   kiocb_clone() onto private_data, then filemap_read()
  .mmap        vma_set_file(vma, realfile)
  .fadvise     vfs_fadvise(file->private_data, ...)
  .splice_read filemap_splice_read

filemap_splice_read() does init_sync_kiocb(&iocb, in), and
filemap_get_pages() then takes iocb->ki_filp->f_mapping (mm/filemap.c:2686),
so it works on the user file's mapping, which after your patch is confirmed
to be the real inode's.  erofs_fill_inode() sets that mapping's a_ops
unconditionally, so the data splice() and sendfile() return is correct, but
they populate the per-file page cache from disk rather than the shared one
read() and mmap() use, caching the same content twice.

Thanks,
Zhan Xusheng