disk.IOCounters() is always an empty map on Darwin

[xxxserxxx]

Describe the bug disk.IOCounters() does not return any information for any disks on Darwin.

To Reproduce

package main

import (
        "fmt"
        "github.com/shirou/gopsutil/disk"
)

func main() {
        ps, err := disk.Partitions(false)
        if err != nil {
                panic(err)
        }
        for _, p := range ps {
                iocs, err := disk.IOCounters(p.Device)
                if err != nil {
                        panic(err)
                }
                fmt.Printf("Dev %s, MP %s, counters = %v\n", p.Device, p.Mountpoint, iocs)
                for k, ioc := range iocs {
                        fmt.Printf("\tcounters[%s] = %v\n", k, ioc)
                }
        }
}

Observed:

MacBook-Air-2:tmp$ go run .
Dev /dev/disk1s1, MP /, counters = map[]
Dev /dev/disk1s4, MP /private/var/vm, counters = map[]

Expected behavior IO counters from the API to not be the empty set.

Environment (please complete the following information):

• [x] Mac OS: [paste the result of sw_vers and uname -a]

MacBook-Air-2:tmp$ sw_vers
ProductName:    Mac OS X
ProductVersion: 10.13.6
BuildVersion:   17G10021
MacBook-Air-2:tmp$ uname -a
Darwin MacBook-Air-2.local 17.7.0 Darwin Kernel Version 17.7.0: Sun Dec  1 19:19:56 PST 2019; root:xnu-4570.71.63~1/RELEASE_X86_64 x86_64

Additional context Not cross-compiling.

MacBook-Air-2:tmp Monika$ go version
go version go1.14.1 darwin/amd64

[xxxserxxx]

So, on OSX there isn't a relationship between partitions and the names under which IOCounters are stored. For example, on this laptop there are two partitions, devices /dev/disk1s1 and ...s4. There is one IOCounter with the name disk0, and no label. So maybe there's an issue with how the devices are mapped? On a system with exactly one hard drive, IOCounter thinks it's called disk0 and the device list has it as /devdisk1....

I haven't dug into the code any further, but I'm going to plug in some USB drives and see if I can identify the naming pattern.

Edit

Interesting.

• The internal hard drive is reported as disk0 by IOCounters() and /dev/disk1s1 by Partitions()
• A USB-C memory stick is reported as disk2 by IOCounters() and /dev/disk2s1 by Partitions() This is going to make guessing at the mapping between the output of these two functions difficult.

The result of IOCounters() on Darwin comes from a C call. @Lomanic, were you the original contributor of this piece of code, and are you able to shed any light on this? I'm quickly getting out of my depth.

Edit 2

IOCounters() names come from the C call; Partitions() comes from a Go library; this probably accounts for the discrepency in naming.

Edit 3

I now believe that this behavior is a consequence of how Apple is handling logical volumes. Using the ghw libray, I see on this machine (only the internal HD, no USB stick):

disk disk0, 2 partitions
        /dev/disk0s1 (300MB) [EFI]
        /dev/disk0s2 (234GB) [Apple_APFS]
disk disk1, 4 partitions
        /dev/disk1s1 (234GB) [APFS Volume] mounted@/
        /dev/disk1s2 (234GB) [APFS Volume]
        /dev/disk1s3 (234GB) [APFS Volume]
        /dev/disk1s4 (234GB) [APFS Volume] mounted@/private/var/vm

disk0 is consistent with IOCounters() naming. However, the second partition is broken up into 4 logical volumes which all show up as disk1. IOCounters() doesn't see disk1 at all, and Partitions() sees only disk1. Partitions() does not, however, see all of the partitions; it only sees the first and last.

Incidentally, this could explain a second issue that's been reported (against gotop) by someone on Linux who's using LVM; if the disk package is having trouble with logical volumes under Darwin, perhaps it's also having difficulty with them under Linux. The bug reports have the same root cause in gotop -- that IOCounters is not matching device names and is returning empty maps.

[Lomanic]

Thanks for the repro case, I see indeed the behavior you describe on my VM. Interesting problem, I don't see an easy solution for the moment, would need more digging.

Regarding Linux, maybe this is the same thing as here https://github.com/shirou/gopsutil/issues/813#issuecomment-572307603