Re: [Qemu-devel] [PATCH 1/3] rcu: Add automatically released rcu_read_lock variant

["Dr. David Alan Gilbert" <dgilbert@redhat.com>]

* Eric Blake (eblake@redhat.com) wrote:
> On 9/11/19 12:40 PM, Eric Blake wrote:
> 
> >> +
> >> +#define RCU_READ_LOCK_AUTO g_auto(rcu_read_auto_t) \
> >> +    _rcu_read_auto = 'x'; \
> > 
> > I'm a bit lost at where _rcu_read_auto is declared.  (I could understand
> > if an earlier macro had created that typedef via concatenating _ with
> > rcu_read_auto_t, but making the preprocessor drop _t is not possible. Is
> > this a typo, and if so, why did the compiler not complain?)
> 
> Okay, I read it wrong.  This rendering would be easier for me to
> understand (you are declaring a dummy variable right here):
> 
> #define RCU_READ_LOCK_AUTO \
>     g_auto(rcu_read_auto_t) _rcu_read_auto = 'x'; \
> ...
> 
> In other words, I'm not used to expecting a split between type and
> variable name across two lines, especially when the type is itself a
> macro call, and where my first reading didn't spot that
> (rcu_read_auto_t) was not the name of the argument to a mixed-case macro
> RCU_READ_LOACK_AUTO_g_auto, rather than g_auto(...) being the start of
> the parameter-less macro RCU_READ_LOCK_AUTO definition.

Yep, that's simplified after the rework Dan suggested.

Dave

> -- 
> Eric Blake, Principal Software Engineer
> Red Hat, Inc.           +1-919-301-3226
> Virtualization:  qemu.org | libvirt.org
> 



--
Dr. David Alan Gilbert / dgilbert@redhat.com / Manchester, UK