Comment 0 for bug 1980848

# Issue description

`arc_summary` no longer works with kernel 5.15. It used to work with previous kernel like 5.13.

# Steps to reproduce

1) setup 20.04 with HWE kernel 5.15
2) install `zfsutils-linux`
3) run `arc_summary`
$ arc_summary
Traceback (most recent call last):
  File "/usr/sbin/arc_summary", line 875, in <module>
    main()
  File "/usr/sbin/arc_summary", line 826, in main
    kstats = get_kstats()
  File "/usr/sbin/arc_summary", line 259, in get_kstats
    with open(PROC_PATH+section, 'r') as proc_location:
FileNotFoundError: [Errno 2] No such file or directory: '/proc/spl/kstat/zfs/xuio_stats'

Indeed, the xuio_stats file isn't there anymore:
$ ll /proc/spl/kstat/zfs/
total 0
dr-xr-xr-x 21 root root 0 Jul 6 10:49 ./
dr-xr-xr-x 4 root root 0 Jul 6 10:49 ../
-rw-r--r-- 1 root root 0 Jul 6 10:49 abdstats
-rw-r--r-- 1 root root 0 Jul 6 10:49 arcstats
dr-xr-xr-x 20 root root 0 Jul 6 10:49 data/
-rw------- 1 root root 0 Jul 6 10:49 dbgmsg
-rw------- 1 root root 0 Jul 6 10:49 dbufs
-rw-r--r-- 1 root root 0 Jul 6 10:49 dbufstats
dr-xr-xr-x 70 root root 0 Jul 6 10:49 default/
-rw-r--r-- 1 root root 0 Jul 6 10:49 dmu_tx
-rw-r--r-- 1 root root 0 Jul 6 10:49 dnodestats
-rw-r--r-- 1 root root 0 Jul 6 10:49 fletcher_4_bench
-rw-r--r-- 1 root root 0 Jul 6 10:49 fm
-rw-r--r-- 1 root root 0 Jul 6 10:49 import_progress
-rw-r--r-- 1 root root 0 Jul 6 10:49 metaslab_stats
-rw-r--r-- 1 root root 0 Jul 6 10:49 vdev_cache_stats
-rw-r--r-- 1 root root 0 Jul 6 10:49 vdev_mirror_stats
-rw-r--r-- 1 root root 0 Jul 6 10:49 vdev_raidz_bench
-rw-r--r-- 1 root root 0 Jul 6 10:49 zfetchstats
-rw-r--r-- 1 root root 0 Jul 6 10:49 zil
-rw-r--r-- 1 root root 0 Jul 6 10:49 zstd

# Workaround

This (naive) patch sidesteps the problem:

$ diff -Naur /usr/sbin/arc_summary.old /usr/sbin/arc_summary
--- /usr/sbin/arc_summary.old 2022-07-06 10:59:50.752833101 -0400
+++ /usr/sbin/arc_summary 2022-07-06 10:59:22.449113169 -0400
@@ -255,6 +255,8 @@
     secs = SECTION_PATHS.values()

     for section in secs:
+ if not os.path.exists(PROC_PATH+section):
+ continue

         with open(PROC_PATH+section, 'r') as proc_location:
             lines = [line for line in proc_location]

# Additional information
$ lsb_release -rd
Description: Ubuntu 20.04.4 LTS
Release: 20.04
$ uname -r
5.15.0-41-generic
$ apt-cache policy zfsutils-linux linux-image-generic-hwe-20.04
zfsutils-linux:
  Installed: 0.8.3-1ubuntu12.14
  Candidate: 0.8.3-1ubuntu12.14
  Version table:
 *** 0.8.3-1ubuntu12.14 500
        500 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
        100 /var/lib/dpkg/status
     0.8.3-1ubuntu12.9 500
        500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
     0.8.3-1ubuntu12 500
        500 http://us.archive.ubuntu.com/ubuntu focal/main amd64 Packages
linux-image-generic-hwe-20.04:
  Installed: 5.15.0.41.44~20.04.13
  Candidate: 5.15.0.41.44~20.04.13
  Version table:
 *** 5.15.0.41.44~20.04.13 400
        400 http://us.archive.ubuntu.com/ubuntu focal-proposed/main amd64 Packages
        100 /var/lib/dpkg/status
     5.13.0.52.59~20.04.31 500
        500 http://us.archive.ubuntu.com/ubuntu focal-updates/main amd64 Packages
        500 http://security.ubuntu.com/ubuntu focal-security/main amd64 Packages
     5.4.0.26.32 500
        500 http://us.archive.ubuntu.com/ubuntu focal/main amd64 Packages