/*
    Copyright (C) 2023  Pasha <pasha@bell01.com>

    This program is free software: you can redistribute it and/or modify
    it under the terms of the GNU General Public License as published by
    the Free Software Foundation, either version 3 of the License, or
    (at your option) any later version.

    This program is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
    GNU General Public License for more details.

    You should have received a copy of the GNU General Public License
    along with this program.  If not, see <https://www.gnu.org/licenses/>.
*/

#include "cgroup_file_handle.h"
#include <errno.h>
#include <fcntl.h>
#include <linux/magic.h>
#include <stdlib.h>
#include <string.h>
#include <sys/stat.h>
#include <sys/types.h>
#include <sys/vfs.h>

#ifndef CGROUP_SUPER_MAGIC
#define CGROUP_SUPER_MAGIC 0x27e0eb
#endif

#ifndef CGROUP2_SUPER_MAGIC
#define CGROUP2_SUPER_MAGIC 0x63677270
#endif

int get_cgroup_file_handle(const char *pathname, char *cgroupfhp) {
  struct statfs sfs;
  int mount_id, fhsize, flags, dirfd, ret, err;
  struct file_handle *fhp;

  err = 1;
  ret = 0;

  err = statfs(pathname, &sfs);
  if (err != 0) {
    fprintf(stderr, "statfs on %s failed: %s\n", pathname, strerror(errno));
    return ret;
  }

  if ((sfs.f_type != (typeof(sfs.f_type))CGROUP2_SUPER_MAGIC)) {
    fprintf(stderr, "%s is not cgroup2 mount.\n", pathname);
    return ret;
  }

  fhsize = sizeof(*fhp);
  fhp = malloc(fhsize);
  if (!fhp) {
    fprintf(stderr, "Cannot allocate memory for get_cgroup_file_handle(...)\n");
    return ret;
  }

  flags = 0;
  dirfd = AT_FDCWD;
  fhp->handle_bytes = CGROUP_FILE_HANDLE_BYTES;
  err = name_to_handle_at(dirfd, pathname, (struct file_handle *)fhp, &mount_id,
                          flags);
  if (err != 0) {
    fprintf(stderr, "name_to_handle_at failed: %s\n", strerror(errno));
    goto clean_exit;
  }

  if (fhp->handle_bytes != CGROUP_FILE_HANDLE_BYTES) {
    fprintf(stderr, "Unexpected handle size: %d. \n", fhp->handle_bytes);
    goto clean_exit;
  }

  memcpy(cgroupfhp, fhp->f_handle,
         sizeof(unsigned char) * CGROUP_FILE_HANDLE_BYTES);
  ret = 1;

clean_exit:
  free(fhp);
  return ret;
}