mailing list of musl libc

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 #define _BSD_SOURCE
#include <unistd.h>
#include <sys/random.h>
#include <pthread.h>
#include <errno.h>

int getentropy(void *buffer, size_t len)
{
	ssize_t ret;
	int cs;

	if (len > 256) {
		errno = EIO;
		return -1;
	}

	pthread_setcancelstate(PTHREAD_CANCEL_DISABLE, &cs);
	ret = getrandom(buffer, len, 0);
	pthread_setcancelstate(cs, 0);

	if (ret != len) {
		if (ret >= 0)
			errno = EIO;
		return -1;
	}
	return 0;
}