我有一个非常简单的测试程序，可以打印出以下数字。

即

int main(int argc, char* argv[])
  struct statvfs vfs;
  statvfs(argv[1], &vfs);
  printf("f_bsize (block size): %lu\n"
       "f_frsize (fragment size): %lu\n"
       "f_blocks (size of fs in f_frsize units): %lu\n"
       "f_bfree (free blocks): %lu\n"
       "f_bavail free blocks for unprivileged users): %lu\n"
       "f_files (inodes): %lu\n"
       "f_ffree (free inodes): %lu\n"
       "f_favail (free inodes for unprivileged users): %lu\n"
       "f_fsid (file system ID): %lu\n"
       "f_flag (mount flags): %lu\n"
       "f_namemax (maximum filename length)%lu\n",
       vfs.f_bsize,
       vfs.f_frsize,
       vfs.f_blocks,
       vfs.f_bfree,
       vfs.f_bavail,
       vfs.f_files,
       vfs.f_ffree,
       vfs.f_favail,
       vfs.f_fsid,
       vfs.f_flag,
       vfs.f_namemax);

       return 0;
    }

打印输出：

f_bsize (block size): 4096
f_frsize (fragment size): 4096
f_blocks (size of fs in f_frsize units): 10534466
f_bfree (free blocks): 6994546
f_bavail free blocks for unprivileged users): 6459417
f_files (inodes): 2678784
f_ffree (free inodes): 2402069
f_favail (free inodes for unprivileged users): 2402069
f_fsid (file system ID): 12719298601114463092
f_flag (mount flags): 4096
f_namemax (maximum filename length)255

df输出根fs：

Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda5             42137864  14159676  25837672  36% /

但是，这是我感到困惑的地方。

25837672 + 14159676！= 42137846（实际上是39997348）

因此，如果我要执行calc 14159676/42137864 * 100，我得到的df打印结果为33％，而不是36％。

但是如果我计算

14159676/39997348 * 100我得到了35％。

为什么所有差异以及df在哪里获得编号42137864？这与到1k块的转换与4k的实际系统块大小有关吗？

这将集成到我的缓存应用程序中，以告诉我驱动器何时处于某个阈值…例如90％，然后再开始释放固定大小为2 ^
n大小的固定大小的块。因此，我需要的是一个可以给我合理准确的使用率的函数。

编辑：我现在可以匹配什么df打印。除了已使用的百分比。这使我们想知道这一切有多精确。片段大小是多少？

unsigned long total = vfs.f_blocks * vfs.f_frsize / 1024;
unsigned long available = vfs.f_bavail * vfs.f_frsize / 1024;
unsigned long free = vfs.f_bfree * vfs.f_frsize / 1024;

printf("Total: %luK\n", total);
printf("Available: %luK\n", available);
printf("Used: %luK\n", total - free);

编辑2：

unsigned long total = vfs.f_blocks * vfs.f_frsize / 1024;
unsigned long available = vfs.f_bavail * vfs.f_frsize / 1024;
unsigned long free = vfs.f_bfree * vfs.f_frsize / 1024;
unsigned long used = total - free;

printf("Total: %luK\n", total);
printf("Available: %luK\n", available);
printf("Used: %luK\n", used);
printf("Free: %luK\n", free);

// Calculate % used based on f_bavail not f_bfree.  This is still giving out a different answer to df???
printf("Use%%: %f%%\n",  (vfs.f_blocks - vfs.f_bavail) / (double)(vfs.f_blocks) * 100.0);

f_bsize (block size): 4096
f_frsize (fragment size): 4096
f_blocks (size of fs in f_frsize units): 10534466
f_bfree (free blocks): 6994182
f_bavail (free blocks for unprivileged users): 6459053
f_files (inodes): 2678784
f_ffree (free inodes): 2402056
f_favail (free inodes for unprivileged users): 2402056
f_fsid (file system ID): 12719298601114463092
f_flag (mount flags): 4096
f_namemax (maximum filename length)255
Total: 42137864K
Available: 25836212K
Used: 14161136K
Free: 27976728K
Use%: 38.686470%

matth@kubuntu:~/dev$ df
Filesystem           1K-blocks      Used Available Use% Mounted on
/dev/sda5             42137864  14161136  25836212  36% /

我得到38％而不是36。如果用f_bfree计算，我得到33％。df是错误的，还是永远不会是准确的？如果是这种情况，那么我想靠保守一点。