Re: [PATCH] add sched_getcpu

[Alexander Monakov <amonakov@ispras.ru>]

On Mon, 29 Feb 2016, Nathan Zadoks wrote:

> This is a GNU extension, but a fairly minor one, for a system call that
> otherwise has no libc wrapper.
> 
> Adding it was discussed previously, without any objections:
> http://www.openwall.com/lists/musl/2015/05/08/24
> ---
>  include/sched.h          |  3 +++
>  src/sched/sched_getcpu.c | 10 ++++++++++
>  2 files changed, 13 insertions(+)
>  create mode 100644 src/sched/sched_getcpu.c
> 
> diff --git a/include/sched.h b/include/sched.h
> index 3e34a72..17f5e06 100644
> --- a/include/sched.h
> +++ b/include/sched.h
> @@ -76,6 +76,9 @@ void free(void *);
>  
>  typedef struct cpu_set_t { unsigned long __bits[128/sizeof(long)]; } cpu_set_t;
>  int __sched_cpucount(size_t, const cpu_set_t *);
> +#ifdef _GNU_SOURCE

This code is already under the same #ifdef.

> +int sched_getcpu(void);
> +#endif
>  int sched_getaffinity(pid_t, size_t, cpu_set_t *);
>  int sched_setaffinity(pid_t, size_t, const cpu_set_t *);
>  
> diff --git a/src/sched/sched_getcpu.c b/src/sched/sched_getcpu.c
> new file mode 100644
> index 0000000..070d6e7
> --- /dev/null
> +++ b/src/sched/sched_getcpu.c
> @@ -0,0 +1,10 @@
> +#define _GNU_SOURCE
> +#include <stdlib.h>

Do you need this include?

> +#include <sched.h>

(this include could also be dropped; I think it's a matter of policy whether
such includes are desirable or not, so please wait for comment from Rich)

> +#include "syscall.h"
> +
> +int sched_getcpu(void) {
> +  int c, s;
> +  s = syscall(SYS_getcpu, &c, NULL, NULL);
> +  return (s == 0) ? c : s;

This is wrong, as it doesn't set errno on error, and does not produce -1. This
should be something like 'return s ? __syscall_ret(s) : c;' or maybe
'return __syscall_ret(s ? s : c);'.

Alexander