Re: [PATCH] kernfs: implement custom llseek method to fix userspace regression

[Valentin Sinitsyn]

On 15.08.2023 20:48, Dan Williams wrote:
> Valentin Sinitsyn wrote:
> [..]
> > > My only concern is whether there are any scenarios where this is not
> > > appropriate. I.e. do a bit more work to define a kernfs_ops instance
> > > specifically for overriding lseek() in this scenario.
> >
> > Not sure I'm getting you here: do you mean something like this?
> >
> > struct inode *inode = is_f_mapping_redefined(file) ? file_inode(file) :
> > file->f_mapping->host;
>
> I meant something like the patch below (incomplete, but shows the idea).
Understood, thanks. I believe the change can be localized even further, 
up to the point where battr->f_mapping is initialized with 
iomem_get_mapping, as it is the only override known to break 
generic_file_llseek().

I'll send the updated patch in a few days.

Best,
Valentin