Re: [PATCH 1/4] ovl: do not open non-data lower file for fsync

[Al Viro <viro@zeniv.linux.org.uk>]

On Fri, Oct 04, 2024 at 11:28:11PM +0100, Al Viro wrote:
> >         /*
> >          * Overlay file f_pos is the master copy that is preserved
> >          * through copy up and modified on read/write, but only real
> >          * fs knows how to SEEK_HOLE/SEEK_DATA and real fs may impose
> >          * limitations that are more strict than ->s_maxbytes for specific
> >          * files, so we use the real file to perform seeks.
> >          */
> >         ovl_inode_lock(inode);
> >         fd_file(real)->f_pos = file->f_pos;
> > in ovl_llseek()?  Get ovl_real_fdget_meta() called by ovl_real_fdget() and
> > have it return 0 with NULL in fd_file(real), and you've got an oops right
> > there, don't you?
> 
> I see... so you rely upon that thing never happening when the last argument of
> ovl_real_fdget_meta() is false, including the call from ovl_real_fdget().
> 
> I still don't like the calling conventions, TBH.  Let me think a bit...

Sorry, I'm afraid I'll have to leave that until tomorrow - over 38C after the sodding
shingles shot really screws the ability to dig through the code ;-/  My apologies...