Disk utilization

Inputting 'd' can get disk utilization:

The proc_disk() function is like this:

void proc_disk(double elapsed)
{
    struct stat buf;
    int ret;
    if (disk_mode == 0) {
        ret = stat("/proc/diskstats", &buf);
        if (ret == 0) {
            disk_mode = DISK_MODE_DISKSTATS;
        } else {
            ret = stat("/proc/partitions", &buf);
            ......
        }
        ......
}

After Linux 2.6, /proc/diskstats replaced /proc/partitions. My Linux kernel's version is 4.19.4, and the /proc/diskstats is like following:

$ cat /proc/diskstats
   8       0 sda 24517099 658117 3634832978 137524335 5161201 1899656 2471640416 126499269 0 15834950 222007107 0 0 0 0
   8       1 sda1 24517060 658117 3634830626 137524328 5147969 1899656 2471640416 126443415 0 15730970 221884500 0 0 0 0
......

While /proc/partitions is very slim:

$ cat /proc/partitions
major minor  #blocks  name

   8        0 1000204632 sda
   8        1 1000203608 sda1
......

For every field's meaning of /proc/diskstats, you can refer I/O statistics fields. BTW, the "Transfers" in above image refers the sum of read and write operations:

void proc_diskstats(double elapsed)
{
    ......
    p->dk[i].dk_xfers = p->dk[i].dk_reads + p->dk[i].dk_writes;
    ......
}