Hello Marc,
On 9/25/19 11:33 AM, Marc Brandis wrote:
> Hello,
>
> I noticed the following documentation error in the online man pages
> (man7.org) for the "sched_getaffinity(2)" system call. It incorrectly
> says that sched_getaffinity returns 0 on success; instead it returns
> the number of bits in the CPU set, which I assume is the number of
I think you mean "bytes", not "bits"
> CPUs (incl. hyperthreading) the system has.
> I am running on Linux kernel 4.15.0-62 in Ubuntu build 18.04. I came
> across it when debugging a multi-threaded program using the call, and
> that program passing a large buffer for the cpuset parameter (8
> kBytes).
>
> It is not just a typo or grammar issue, but I still was not sure
> whether this should be reported through Bugzilla.
The explanation for what you are seeing is actually covered
lower in the page:
C library/kernel differences
...
On success, the raw sched_getaffinity() system call returns the
number of bytes placed copied into the mask buffer; this will be
the minimum of cpusetsize and the size (in bytes) of the cpumask_t
data type that is used internally by the kernel to represent the
CPU set bit mask.
But, you're not the first to miss this detail, so I've just now modified
the RETURN VALUE section to make it easier for people to find that text:
On success, sched_setaffinity() and sched_getaffinity() return 0
(but see "C library/kernel differences" below, which notes that
the underlying sched_getaffinity() differs in its return value).
Thanks,
Michael
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
