Re: [PATCH v6 06/20] liveupdate: luo_file: implement file systems callbacks

[Mike Rapoport]

On Mon, Nov 17, 2025 at 12:50:56PM -0500, Pasha Tatashin wrote:
> > > +struct liveupdate_file_handler;
> > > +struct liveupdate_session;
> >
> > Why struct liveupdate_session is a part of public LUO API?
> 
> It is an obscure version of private "struct luo_session", in order to
> give subsystem access to:
> liveupdate_get_file_incoming(s, token, filep)
> liveupdate_get_token_outgoing(s, file, tokenp)
> 
> For example, if your FD depends on another FD within a session, you
> can check if another FD is already preserved via
> liveupdate_get_token_outgoing(), and during retrieval time you can
> retrieve the "struct file" for your dependency.
 
And it's essentially unused right now.

> > > +     }
> > > +
> > > +     return 0;
> > > +
> > > +exit_err:
> > > +     fput(file);
> > > +     luo_session_free_files_mem(session);
> >
> > The error handling in this function is a mess. Pasha, please, please, use
> > goto consistently.
> 
> How is this a mess? There is a single exit_err destination, no
> exception, no early returns except at the very top of the function
> where we do early returns before fget() which makes total sense.
> 
> Do you want to add a separate destination for
> luo_session_free_files_mem() ? But that is not necessary, in many
> places it is considered totally reasonable for free(NULL) to work
> correctly...

You have a mix of releasing resources with goto or inside if (err).
And while basic free() primitives like kfree() and vfree() work correctly
with NULL as a parameter, luo_session_free_files_mem() is already not a
basic primitive and it may grow with a time. It already has two conditions
that essentially prevent anything from freeing and this will grow with the
time.

So yes, I want a separate goto destination for freeing each resource and a
goto for 

	err = fh->ops->preserve(&args);
	if (err)

case.

> > > +             luo_file = kzalloc(sizeof(*luo_file), GFP_KERNEL);
> > > +             if (!luo_file)
> > > +                     return -ENOMEM;
> >
> > Shouldn't we free files allocated on the previous iterations?
> 
> No, for the same reason explained in luo_session.c :-)

A comment here as well please :)

> > > +int liveupdate_get_file_incoming(struct liveupdate_session *s, u64 token,
> > > +                              struct file **filep)
> > > +{
> >
> > Ditto.
> 
> These two functions are part of the public API allowing dependency
> tracking for vfio->iommu->memfd during preservation.

So like with FLB, until we get actual users for them they are dead code. 
And until it's clear how exactly dependency tracking for vfio->iommu->memfd
will work, we won't know if this API is useful at all or we'll need
something else in the end.

-- 
Sincerely yours,
Mike.