Messages in this thread | | | Date | Wed, 27 Jan 2016 17:31:58 +0000 (UTC) | From | Mathieu Desnoyers <> | Subject | Re: [RFC PATCH v2 1/3] getcpu_cache system call: cache CPU number of running thread |
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----- On Jan 27, 2016, at 12:22 PM, Thomas Gleixner tglx@linutronix.de wrote:
> On Wed, 27 Jan 2016, Mathieu Desnoyers wrote: >> +/* >> + * sys_getcpu_cache - setup getcpu cache for caller thread >> + */ >> +SYSCALL_DEFINE2(getcpu_cache, int32_t __user **, cpu_cachep, int, flags) >> +{ >> + int32_t __user *cpu_cache; >> + >> + if (unlikely(flags)) >> + return -EINVAL; >> + /* Check if cpu_cache is already registered. */ >> + if (current->cpu_cache) { >> + if (put_user(current->cpu_cache, cpu_cachep)) >> + return -EFAULT; >> + return 0; >> + } > > This is really odd. How is the caller supposed to differentiate between: > > 1) Get the installed cpucache pointer > > 2) Set the cpucache pointer > > We really want clearly seperated functionality here. > > getcpu_cache(ptr, GET_CACHEP); > > and > > getcpu_cache(ptr, SET_CACHEP); > > Returns -EBUSY if current->cpu_cache is already set, except we allow > replacing the pointer.
Sounds fair. What is the recommended typing for "ptr" then ? uint32_t ** or uint32_t * ?
It would be expected to pass a "uint32_t *" for the set operation, but the "get" operation requires a "uint32_t **".
Also, I'd be tempted to put the GET/SET operation selector as a first parameter.
Thanks,
Mathieu
> > Thanks, > > tglx
-- Mathieu Desnoyers EfficiOS Inc. http://www.efficios.com
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