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    SubjectRe: [PATCH] cpumask 5/10 rewrite cpumask.h - single bitmap based implementation
    William Lee Irwin III wrote:
    > Some interface is needed to export NR_CPUS

    Well ... technically ... such an interface already exists.
    However the word "interface" might be too kind a description.

    * Ugly hack to get size of cpumask - keep calling sched_getaffinity
    * with masks of increasing size until it stops complaining -EINVAL
    * that the mask is too small. Determines size of kernel cpumask,
    * in number of bytes. Size will always be some multiple of the
    * size of an unsigned long. Since it's ok to be too big, and since
    * kernel NR_CPUS is usually a power of two, just try each power
    * of two, until one works. Contrary to the man page, a successful
    * sched_getaffinity() returns a positive number (the sizeof(cpumask_t),
    * to be exact), not zero. Consider any return >= 0 to mean success.

    #include <errno.h>
    extern int errno;

    int cpumasksz()
    int nbytes;
    unsigned long *mask = 0;

    for (nbytes = sizeof(unsigned long); nbytes < 10000; nbytes *= 2) {
    int r;
    mask = (unsigned long *)realloc(mask, nbytes);
    if (mask == 0)
    return -ENOMEM;
    errno = 0;
    r = sched_getaffinity(0, nbytes, mask);
    if (r < 0 && errno == EINVAL)
    if (r >= 0)
    return -errno;
    return nbytes;

    I won't rest till it's the best ...
    Programmer, Linux Scalability
    Paul Jackson <> 1.650.933.1373
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      Last update: 2005-03-22 14:03    [W:0.025 / U:110.028 seconds]
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