Re: [MINIOS PATCH v3 03/12] use alloc_file_type() and get_file_from_fd() in xs

[Juergen Gross <jgross@xxxxxxxx>]

On 18.01.22 15:29, Andrew Cooper wrote:
> On 16/01/2022 08:33, Juergen Gross wrote:
> > diff --git a/lib/xs.c b/lib/xs.c
> > index 4af0f960..c12341aa 100644
> > --- a/lib/xs.c
> > +++ b/lib/xs.c
> > @@ -18,23 +18,56 @@ static inline int _xs_fileno(struct xs_handle *h) {
> >       return (intptr_t) h;
> >   }
> >   
> > +static int xs_close_fd(struct file *file)
> > +{
> > +    struct xenbus_event *event, *next;
> > +
> > +    for (event = file->dev; event; event = next)
> > +    {
> > +        next = event->next;
> > +        free(event);
> > +    }
> > +
> > +    return 0;
> > +}
> > +
> > +static bool xs_can_read(struct file *file)
> > +{
> > +    return file && file->dev;
> Just 'return file->dev;' ?
Yes.

> > @@ -169,18 +202,20 @@ char **xs_directory(struct xs_handle *h, xs_transaction_t 
> > t,
> >   
> >   bool xs_watch(struct xs_handle *h, const char *path, const char *token)
> >   {
> > -    int fd = _xs_fileno(h);
> > +    struct file *file = get_file_from_fd(_xs_fileno(h));
> > +
> >       printk("xs_watch(%s, %s)\n", path, token);
> >       return xs_bool(xenbus_watch_path_token(XBT_NULL, path, token,
> > -                   (xenbus_event_queue *)&files[fd].dev));
> > +                   (xenbus_event_queue *)&file->dev));
> This is utterly mad.  In particular, close() looks to be very racy with
> new watches arriving.
In practice it should be no problem, though (closing the file in one
thread while the other one is adding a watch would be rather strange).

Additionally close() for xenbus in Mini-OS is called only when stopping
the domain today.

> However, can the indentation at least be fixed here as the line is
> changing.  That's a parameter to xenbus_watch_path_token(), not xs_bool().
Yes, that should be done.

> > diff --git a/xenbus/xenbus.c b/xenbus/xenbus.c
> > index b687678f..785389fb 100644
> > --- a/xenbus/xenbus.c
> > +++ b/xenbus/xenbus.c
> > @@ -393,6 +393,7 @@ static int allocate_xenbus_id(void)
> >   void init_xenbus(void)
> >   {
> >       int err;
> > +
> Spurious hunk?
Yes.


Juergen

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