Re: [Xen-devel] Re: [PATCH 1/2] xen/event: Add reference counting to event channel

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Mon, 2011-10-24 at 21:22 +0100, Konrad Rzeszutek Wilk wrote:
> 
> > +void evtchn_put(unsigned int evtchn)
> 
> The decleration for 'evtchn' is 'unsigned short' so that can be
> used instead of 'unsigned int'.

I think I nearly made the same comment but then I looked at
drivers/xen/events.c and found that it uses "unsigned", "unsigned
short", "unsigned int" and "int" fairly interchangeably. The externally
visible API (i.e. include/xen/events.h) tends to stick to just "unsigned
int" or "int".

The problem with the short types is that they don't leave room for an
error indication, which is why on the Xen tools (libxc) side we have his
piece of minor ugliness:
        typedef int evtchn_port_or_error_t;

The actual hypercall interface uses "typedef uint32_t evtchn_port_t" but
AIUI real evtchn values are guaranteed to fit in 31 bits.

Ian.


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