Re: [Xen-devel] [PATCH 5 of 7 v2] blktap3/tapback: Introduce front-end XenStore path handler

[Thanos Makatos <thanos.makatos@xxxxxxxxxx>]

> On Fri, 2013-01-04 at 12:14 +0000, Thanos Makatos wrote:
> > +static inline int
> > +blkback_frontend_changed(vbd_t * const xbdev, const XenbusState
> state)
> > +{
> > +    /*
> > +     * XXX The size of the array (9) comes from the XenbusState
> enum.
> > +     *
> > +     * TODO Send a patch that adds XenbusStateMin, XenbusStateMax,
> > +     * XenbusStateInvalid and in the XenbusState enum (located in
> xenbus.h).
> > +     */
> > +    struct frontend_state_change {
> > +        int (*fn)(vbd_t * const, const XenbusState);
> > +        const XenbusState state;
> 
> Is this the next backend state or the current or?...
> 
> > +    } static const frontend_state_change_map[] = {
> > +        {NULL, 0},                                          /*
> Unknown */
> 
>       [XenbusStateUnknown] = {NULL,0},
>       [XenbusStateInitialising] = {tapback_device_switch_state,
> XenbusStateInitWait},
> 
> ? Bit less error prone.
> 
> > +        {tapback_device_switch_state, XenbusStateInitWait}, /*
> Initialising */
> > +        {NULL, 0},                                          /*
> InitWait */
> > +        {blkback_connect_tap, 0},                           /*
> Initialised */
> > +        {blkback_connect_tap, 0},                           /*
> Connected */
> > +        {tapback_device_switch_state, XenbusStateClosing},  /*
> Closing */
> > +        {backend_close, 0},                                 /*
> StateClosed */
> > +        {NULL, 0},                                          /*
> Reconfiguring */
> > +        {NULL, 0}                                           /*
> Reconfigured */
> > +    };

The position of each element in the frontend_state_change_map array reflects 
the state into which the front-end just switched. Each element contains a 
call-back function to be executed in response, and an optional state for the 
back-end to switch to. Does this make sense? Actually, there was a switch 
statement and I replaced it with this in order to make it less error-prone!
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