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

[Eric Blake]

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.

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

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