Linuxで簡単dfコマンド

dfコマンドはstatfs()を使って作るだけ。statvfs()でもいいけど.
setmntent(),endmntent() は中身は fopen()/fclose() だから使わないくても/etc/mtab直接みてもいいかな。

human-readableオプションや、excludeオプションなど、高機能な部分をなくした骨子はこんな感じでしょうか。

df.c

# include <mntent.h>
# include <stdio.h>
# include <stdlib.h>
# include <string.h>
# include <sys/stat.h>
# include <sys/types.h>
# include <sys/vfs.h>
# include <unistd.h>

typedef struct _df_t {
   struct mntent* mnt;
   struct statfs* fs;
} DfData;

int get_mount_record(FILE* mtab, DfData* df)
{
  df->mnt = getmntent(mtab);
  if (df->mnt) {
    if (df->mnt->mnt_dir == NULL) return 0;
    if (statfs(df->mnt->mnt_dir, df->fs) != 0) return 0;
    return 1;
  }
  return 0;
}

# define DF_KILO_RECORD_FMT  "%-25s %10lu %10lu %10lu %4s %-10s\n"

void print_kilobyte(DfData* df) {
  size_t total_size = df->fs->f_blocks * df->fs->f_bsize / 1024;
  size_t avail_size = df->fs->f_bavail * df->fs->f_bsize / 1024;
  size_t used_size = total_size - avail_size;
  char percent[4] = {0};
  if (df->fs->f_blocks == 0)
     snprintf(percent, sizeof(percent), "-");
  else
     snprintf(percent, sizeof(percent), "%lu%%", (100 * used_size / total_size));

  printf(DF_KILO_RECORD_FMT, df->mnt->mnt_fsname, total_size, used_size, avail_size, percent, df->mnt->mnt_dir);
  return;
}

void show_kilobyte(FILE* mtab) {
  DfData* df = (DfData*)malloc(sizeof(DfData));
  df->fs = (struct statfs *)malloc(sizeof(struct statfs));

  while(get_mount_record(mtab, df))
       print_kilobyte(df);

  free(df->fs);
  free(df);
  return;
}

int main(void)
{
  FILE* mtab = setmntent(_PATH_MOUNTED, "r");
  show_kilobyte(mtab);
  endmntent(mtab);
  exit(0);
}

実行結果。

$ gcc -Wall -Wextra -O2 df.o -o df
$ ./df
rootfs                      30909700   19431160   11478540  62% /
sysfs                              0          0          0    - /sys
proc                               0          0          0    - /proc
devtmpfs                     2441664          0    2441664   0% /dev
securityfs                         0          0          0    - /sys/kernel/security
tmpfs                        2325352          0    2325352   0% /dev/shm
devpts                             0          0          0    - /dev/pts
tmpfs                        2325352       8676    2316676   0% /run
tmpfs                        2325352          0    2325352   0% /sys/fs/cgroup
cgroup                             0          0          0    - /sys/fs/cgroup/systemd
pstore                             0          0          0    - /sys/fs/pstore
cgroup                             0          0          0    - /sys/fs/cgroup/cpuset
cgroup                             0          0          0    - /sys/fs/cgroup/pids
cgroup                             0          0          0    - /sys/fs/cgroup/net_cls,net_prio
cgroup                             0          0          0    - /sys/fs/cgroup/blkio
cgroup                             0          0          0    - /sys/fs/cgroup/perf_event
cgroup                             0          0          0    - /sys/fs/cgroup/devices
cgroup                             0          0          0    - /sys/fs/cgroup/freezer
cgroup                             0          0          0    - /sys/fs/cgroup/hugetlb
cgroup                             0          0          0    - /sys/fs/cgroup/cpu,cpuacct
cgroup                             0          0          0    - /sys/fs/cgroup/memory
configfs                           0          0          0    - /sys/kernel/config
/dev/mapper/centos-root     30909700   19431160   11478540  62% /
systemd-1                          0          0          0    - /proc/sys/fs/binfmt_misc
mqueue                             0          0          0    - /dev/mqueue
hugetlbfs                          0          0          0    - /dev/hugepages
debugfs                            0          0          0    - /sys/kernel/debug
binfmt_misc                        0          0          0    - /proc/sys/fs/binfmt_misc
nfsd                               0          0          0    - /proc/fs/nfsd
/dev/xvda1                    508588     296336     212252  58% /boot
sunrpc                             0          0          0    - /var/lib/nfs/rpc_pipefs
none                               0          0          0    - /proc/xen
tmpfs                         465072          0     465072   0% /run/user/1000