cloexec.c

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// SPDX-License-Identifier: GPL-2.0
#include <errno.h>
#include <sched.h>
#include "util.h"
#include "../perf.h"
#include "cloexec.h"
#include "asm/bug.h"
#include "debug.h"
#include <unistd.h>
#include <asm/unistd.h>
#include <sys/syscall.h>

static unsigned long flag = PERF_FLAG_FD_CLOEXEC;

int __weak sched_getcpu(void)
{
#ifdef __NR_getcpu
    unsigned cpu;
    int err = syscall(__NR_getcpu, &cpu, NULL, NULL);
    if (!err)
        return cpu;
#else
    errno = ENOSYS;
#endif
    return -1;
}

static int perf_flag_probe(void)
{
    /* use 'safest' configuration as used in perf_evsel__fallback() */
    struct perf_event_attr attr = {
        .type = PERF_TYPE_SOFTWARE,
        .config = PERF_COUNT_SW_CPU_CLOCK,
        .exclude_kernel = 1,
    };
    int fd;
    int err;
    int cpu;
    pid_t pid = -1;
    char sbuf[STRERR_BUFSIZE];

    cpu = sched_getcpu();
    if (cpu < 0)
        cpu = 0;

    /*
     * Using -1 for the pid is a workaround to avoid gratuitous jump label
     * changes.
     */
    while (1) {
        /* check cloexec flag */
        fd = sys_perf_event_open(&attr, pid, cpu, -1,
                     PERF_FLAG_FD_CLOEXEC);
        if (fd < 0 && pid == -1 && errno == EACCES) {
            pid = 0;
            continue;
        }
        break;
    }
    err = errno;

    if (fd >= 0) {
        close(fd);
        return 1;
    }

    WARN_ONCE(err != EINVAL && err != EBUSY,
          "perf_event_open(..., PERF_FLAG_FD_CLOEXEC) failed with unexpected error %d (%s)\n",
          err, str_error_r(err, sbuf, sizeof(sbuf)));

    /* not supported, confirm error related to PERF_FLAG_FD_CLOEXEC */
    while (1) {
        fd = sys_perf_event_open(&attr, pid, cpu, -1, 0);
        if (fd < 0 && pid == -1 && errno == EACCES) {
            pid = 0;
            continue;
        }
        break;
    }
    err = errno;

    if (fd >= 0)
        close(fd);

    if (WARN_ONCE(fd < 0 && err != EBUSY,
              "perf_event_open(..., 0) failed unexpectedly with error %d (%s)\n",
              err, str_error_r(err, sbuf, sizeof(sbuf))))
        return -1;

    return 0;
}

unsigned long perf_event_open_cloexec_flag(void)
{
    static bool probed;

    if (!probed) {
        if (perf_flag_probe() <= 0)
            flag = 0;
        probed = true;
    }

    return flag;
}