/*
 * Copyright © 2018 Alexey Dobriyan <adobriyan@gmail.com>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
 * ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
 * ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
 * OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 */
// Test
// 1) read and lseek on every file in /proc
// 2) readlink of every symlink in /proc
// 3) recursively (1) + (2) for every directory in /proc
// 4) write to /proc/*/clear_refs and /proc/*/task/*/clear_refs
// 5) write to /proc/sysrq-trigger
#undef NDEBUG
#include <assert.h>
#include <errno.h>
#include <sys/types.h>
#include <dirent.h>
#include <stdbool.h>
#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/vfs.h>
#include <fcntl.h>
#include <unistd.h>

#include "proc.h"

static void f_reg(DIR *d, const char *filename)
{
        char buf[4096];
        int fd;
        ssize_t rv;

        /* read from /proc/kmsg can block */
        fd = openat(dirfd(d), filename, O_RDONLY|O_NONBLOCK);
        if (fd == -1)
                return;
        /* struct proc_ops::proc_lseek is mandatory if file is seekable. */
        (void)lseek(fd, 0, SEEK_SET);
        rv = read(fd, buf, sizeof(buf));
        assert((0 <= rv && rv <= sizeof(buf)) || rv == -1);
        close(fd);
}

static void f_reg_write(DIR *d, const char *filename, const char *buf, size_t len)
{
        int fd;
        ssize_t rv;

        fd = openat(dirfd(d), filename, O_WRONLY);
        if (fd == -1)
                return;
        rv = write(fd, buf, len);
        assert((0 <= rv && rv <= len) || rv == -1);
        close(fd);
}

static void f_lnk(DIR *d, const char *filename)
{
        char buf[4096];
        ssize_t rv;

        rv = readlinkat(dirfd(d), filename, buf, sizeof(buf));
        assert((0 <= rv && rv <= sizeof(buf)) || rv == -1);
}

static void f(DIR *d, unsigned int level)
{
        struct dirent *de;

        de = xreaddir(d);
        assert(de->d_type == DT_DIR);
        assert(streq(de->d_name, "."));

        de = xreaddir(d);
        assert(de->d_type == DT_DIR);
        assert(streq(de->d_name, ".."));

        while ((de = xreaddir(d))) {
                assert(!streq(de->d_name, "."));
                assert(!streq(de->d_name, ".."));

                switch (de->d_type) {
                        DIR *dd;
                        int fd;

                case DT_REG:
                        if (level == 0 && streq(de->d_name, "sysrq-trigger")) {
                                f_reg_write(d, de->d_name, "h", 1);
                        } else if (level == 1 && streq(de->d_name, "clear_refs")) {
                                f_reg_write(d, de->d_name, "1", 1);
                        } else if (level == 3 && streq(de->d_name, "clear_refs")) {
                                f_reg_write(d, de->d_name, "1", 1);
                        } else {
                                f_reg(d, de->d_name);
                        }
                        break;
                case DT_DIR:
                        fd = openat(dirfd(d), de->d_name, O_DIRECTORY|O_RDONLY);
                        if (fd == -1)
                                continue;
                        dd = fdopendir(fd);
                        if (!dd)
                                continue;
                        f(dd, level + 1);
                        closedir(dd);
                        break;
                case DT_LNK:
                        f_lnk(d, de->d_name);
                        break;
                default:
                        assert(0);
                }
        }
}

int main(void)
{
        DIR *d;
        struct statfs sfs;

        d = opendir("/proc");
        if (!d)
                return 4;

        /* Ensure /proc is proc. */
        if (fstatfs(dirfd(d), &sfs) == -1) {
                return 1;
        }
        if (sfs.f_type != 0x9fa0) {
                fprintf(stderr, "error: unexpected f_type %lx\n", (long)sfs.f_type);
                return 2;
        }

        f(d, 0);

        return 0;
}