arc_summary | head -> broken pipe

[devZer0]

Distribution Name | debian buster / proxmox
Distribution Version | 10.9
Linux Kernel | 5.4.106-1-pve
Architecture | x86_64
ZFS Version | 2.0.4-pve1
SPL Version | 2.0.4-pve1

Describe the problem you're observing

when piping output arc_summary to head util for example, i'm getting weird behaviour

# arc_summary |head

------------------------------------------------------------------------
ZFS Subsystem Report                            Wed May 12 22:07:21 2021
Linux 5.4.106-1-pve                                           2.0.4-pve1
Machine: pbs01 (x86_64)                                       2.0.4-pve1

ARC status:                                                      HEALTHY
        Memory throttle count:                                         0

ARC size (current):                                    48.8 %    2.9 GiB
Traceback (most recent call last):
  File "/usr/sbin/arc_summary", line 875, in <module>
    main()
  File "/usr/sbin/arc_summary", line 869, in main
    section_calls[section](kstats)
  File "/usr/sbin/arc_summary", line 756, in section_tunables
    print(format_raw_line(key, value))
BrokenPipeError: [Errno 32] Broken pipe

same command another run

# arc_summary |head

------------------------------------------------------------------------
ZFS Subsystem Report                            Wed May 12 22:07:23 2021
Linux 5.4.106-1-pve                                           2.0.4-pve1
Machine: pbs01 (x86_64)                                       2.0.4-pve1

ARC status:                                                      HEALTHY
        Memory throttle count:                                         0

ARC size (current):                                    48.8 %    2.9 GiB
Exception ignored in: <_io.TextIOWrapper name='<stdout>' mode='w' encoding='UTF-8'>
BrokenPipeError: [Errno 32] Broken pipe

[gdevenyi]

Just this:
https://linuxpip.org/broken-pipe-python-error/

[rincebrain]

Seems like round two of #6965 - maybe the patch for this got lost in the interim.

edit: Yup, my memory was right - arc_summary got replaced by a rewrite in the interim, and it has the same problem the original once did.

And unfortunately, I think the test case added to catch this might not work because it catches the last error in the pipeline, and head isn't the thing erroring.

I think set -o pipefail would be enough to make this behave the way that was desired even in ksh...

Edit 2: PR incoming...