Re: Re: [PATCH v2] fuse: honor desc offset in readahead reads

[Horst Birthelmer <horst@birthelmer.de>]

On Fri, Jul 17, 2026 at 10:56:20AM +0200, Miklos Szeredi wrote:
> On Fri, 17 Jul 2026 at 05:28, Haofeng Li <lihaofeng@kylinos.cn> wrote:
> >
> > fuse_handle_readahead records non-zero descs[].offset when
> > iomap skips leading uptodate blocks in a folio, but
> > fuse_send_readpages built FUSE_READ from folio_pos() alone.
> > The reply was still copied at descs[0].offset, so wrong
> > file data was placed into the page cache.
> >
> > Add descs[0].offset to the request position. Apply the
> > same correction in fuse_short_read for EOF size updates.
> >
> > Fixes: 4ea907108a5c ("fuse: use iomap for readahead")
> > Signed-off-by: Haofeng Li <lihaofeng@kylinos.cn>
> > Reviewed-by: Joanne Koong <joannelkoong@gmail.com>
> 
> Sashiko founds some more cases:
> https://sashiko.dev/#/patchset/20260717032835.922433-1-lihaofeng%40kylinos.cn
> 
> This is a large folio issue, right?  I do wonder why fsx-linux missed
> these with the large folios enabled.

I think it probably never occured since fuse_readahead() only fills in folio boundaries?
This could be coincidence or readahead controls 'job'. I'm not that familiar with that code.

I just got suspicious on your question, since I have large folios enabled in testing, too, and
have not seen the case.

> 
> Thanks,
> Miklos
>