文件系统-4-struct file_operations 结构

一、各回调简介

1. flush和close回调的关系

实测，dev设备节点每次 close(fd) 都会调用一次 fops->flush() 回调，当 file->f_count 减为0后调用 fops->close() 回调; 而proc文件节点则不会调用 fops->flush() 回调，只会在 file->f_count 减为0后调用 fops->close() 回调。

实验代码：

#include <signal.h>
#include <unistd.h>
#include <stdio.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <sys/prctl.h>
#include <fcntl.h>
#include <stdlib.h>
#include <errno.h>
#include <string.h>

int proc_file_node_test(int argc, char *argv[])
{
    int fd, fd1, fd2, fd3, ret;
    char *str_val = "4";

    if (argc < 2 || atoi(argv[1]) != 1)
        return -1;

    if (argc == 3)
        str_val = argv[2];

    fd = open("/proc/my_debug", O_RDWR);
    if (fd < 0) {
        fprintf(stderr,"%s: open failed: %d:%s\n", __func__, fd, strerror(errno));
        return -1;
    }

    fd1 = dup(fd);
    fd2 = dup(fd);
    fd3 = dup(fd);

    ret = write(fd, str_val, strlen(str_val));
    if (ret < 0) {
        fprintf(stderr,"%s: write failed: %d:%s\n", __func__, ret, strerror(errno));
        return -1;
    }

    close(fd3);
    close(fd2);
    close(fd1);
    close(fd);

    return 0;
}

int dev_node_test(int argc, char *argv[])
{
    int fd, fd1, fd2, fd3;
    char *str_val = "4";

    if (argc < 2 || atoi(argv[1]) != 2)
        return -1;

    prctl(PR_SET_NAME, "ham_dev_test", NULL, NULL, NULL);

    if (argc == 3) {
        str_val = argv[2];
        fprintf(stderr,"%s: str_val=%s\n", __func__, str_val);
    }

    fd = open("/dev/binder", O_RDWR);
    if (fd < 0) {
        fprintf(stderr,"%s: open failed: %d:%s\n", __func__, fd, strerror(errno));
        return -1;
    }

    fd1 = dup(fd);
    fd2 = dup(fd);
    fd3 = dup(fd);

    close(fd3);
    close(fd2);
    close(fd1);
    close(fd);

    return 0;
}

int main(int argc, char *argv[])
{
    proc_file_node_test(argc, argv);
    dev_node_test(argc, argv);
    return 0;
}

测试结果:

8155:/data/local/tmp # ./my_dup_test 1
8155:/data/local/tmp # dmesg -c | grep HAM
[  155.472931] (6)[7323:my_dup_test]HAM: proc_my_debug_open called
[  155.479231] (6)[7323:my_dup_test]HAM: proc_my_debug_write: set debug=4
[  155.507279] (6)[7323:my_dup_test]HAM: proc_my_debug_release called

8155:/data/local/tmp # ./my_dup_test 2
8155:/data/local/tmp # dmesg -c | grep HAM
[   90.478820] (4)[6984:ham_dev_test]HAM: binder_open called.
[   90.478932] (6)[6984:ham_dev_test]HAM: binder_flush called.
[   90.485913] (6)[6984:ham_dev_test]HAM: binder_flush called.
[   90.491850] (6)[6984:ham_dev_test]HAM: binder_flush called.
[   90.497757] (6)[6984:ham_dev_test]HAM: binder_flush called.
[   90.503616] (3)[5269:OtaUeIoThd]HAM: binder_release called.