Re: [PATCH v2 12/17] xen/hypfs: add new enter() and exit() per node callbacks

[Jürgen Groß <jgross@xxxxxxxx>]

On 03.12.20 15:59, Jan Beulich wrote:
> On 01.12.2020 09:21, Juergen Gross wrote:
> > In order to better support resource allocation and locking for dynamic
> > hypfs nodes add enter() and exit() callbacks to struct hypfs_funcs.
> >
> > The enter() callback is called when entering a node during hypfs user
> > actions (traversing, reading or writing it), while the exit() callback
> > is called when leaving a node (accessing another node at the same or a
> > higher directory level, or when returning to the user).
> >
> > For avoiding recursion this requires a parent pointer in each node.
> > Let the enter() callback return the entry address which is stored as
> > the last accessed node in order to be able to use a template entry for
> > that purpose in case of dynamic entries.
> I guess I'll learn in subsequent patches why this is necessary /
> useful. Right now it looks odd for the function to simple return
> the incoming argument, as this way it's clear the caller knows
> the correct value already.
Basically for dynamic entries based on a template the entry function
will return the address of template->e instead of the dynamic entry
itself. This will enable to have the standard entry functions for
any nodes being linked to the template.

> > @@ -100,11 +112,58 @@ static void hypfs_unlock(void)
> >       }
> >   }
> >   
> > +const struct hypfs_entry *hypfs_node_enter(const struct hypfs_entry *entry)
> > +{
> > +    return entry;
> > +}
> > +
> > +void hypfs_node_exit(const struct hypfs_entry *entry)
> > +{
> > +}
> > +
> > +static int node_enter(const struct hypfs_entry *entry)
> > +{
> > +    const struct hypfs_entry **last = &this_cpu(hypfs_last_node_entered);
> > +
> > +    entry = entry->funcs->enter(entry);
> > +    if ( IS_ERR(entry) )
> > +        return PTR_ERR(entry);
> > +
> > +    ASSERT(!*last || *last == entry->parent);
> > +
> > +    *last = entry;
> > +
> > +    return 0;
> > +}
> > +
> > +static void node_exit(const struct hypfs_entry *entry)
> > +{
> > +    const struct hypfs_entry **last = &this_cpu(hypfs_last_node_entered);
> > +
> > +    if ( !*last )
> > +        return;
> Under what conditions is this legitimate to happen? IOW shouldn't
> there be an ASSERT_UNREACHABLE() here?
This is for the "/" node.


Juergen

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