小编典典

正确将statvfs转换为可用百分比

linux

我有一个非常简单的测试程序,可以打印出以下数字。

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。


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2020-06-07

共1个答案

小编典典

df的数据可能基于而f_bavail不是f_bfree。您可能会发现查看df源代码以了解其工作方式很有帮助。它有许多需要处理的极端情况(例如,当使用的空间超出了非root用户可用的空间量时),但是正常情况的相关代码如下:

  uintmax_t u100 = used * 100;
  uintmax_t nonroot_total = used + available;
  pct = u100 / nonroot_total + (u100 % nonroot_total != 0);

换句话说100 * used / (used + available),四舍五入。插入df输出中的值,得到100 * 14159676 / (14159676 + 25837672) = 35.4015371,舍入为36%,与df计算得出的一样。

2020-06-07