Re: [Xenomai-help] pipe fun

[Philippe Gerum <rpm@xenomai.org>]

Dmitry Adamushko wrote:
> Philippe Gerum <rpm@xenomai.org> wrote on 21.11.2005 13:36:41:
> 
>  > Dmitry Adamushko wrote:
>  > > Ignacio García Pérez <iggarpe@domain.hid> wrote on 21.11.2005 12:24:57:
>  > >
>  > >  > Dmitry Adamushko wrote:
>  > >  >
>  > >  > >            /* Return buffer is too small - message is lost. */
>  > >  > >            ret = -ENOSPC; <---- That's the error you are getting.
>  > >  > >
>  > >  > Maybe "No space left on device" is a bit misleading. Wouldn't 
> ENOMEM fit
>  > >  > better? (or event EINVAL)
>  > >  >
>  > >
>  > > Actually, looking now at the linux sources, -ENOSPC is used for
>  > > describing the same reason (buffer is not big enough) in some places;
>  > > although there is, at least, one more value -ENOBUFS that's used 
> for the
>  > > same reason.
>  > >
>  > > #define ENOSPC          28      /* No space left on device */
>  > > #define ENOBUFS         105     /* No buffer space available */
>  > >
>  > > So it looks like both may be used in the same context but, I guess, a
>  > > definition of -ENOBUFS is less confusing.
>  > >
>  > >
>  >
>  > Let's fix this.
>  >
> 
> Enclosed.
> 

Applied, thanks.

> One more thing about xnpipe_read() though.
> 
> 
> ...
>            }
>        else
>            /* Return buffer is too small - message is lost. */
>            ret = -ENOBUFS;
> 
> So the message is lost in such a case. We may easily avoid that by 
> making a proper check of the size when we are still in the locked 
> section and putting the message back into the queue (prependq() of 
> course). I think that would be more sane.
>

Problem is that if nobody ends up reading the message because the 
application always passes invalid args, internal heap memory may be 
exhausted due to unread messages.

> 
>  > --
>  >
>  > Philippe.
> 
> ---
> Best regards,
> Dmitry
> 
> /(See attached file: pipe-ENOBUFS.patch)//(See attached file: 
> ChangeLog.patch)/
> 


-- 

Philippe.