zed_guid_to_pool() broken on hosts with dash as /bin/sh

[ZNikke]

System information

Type	Version/Name
Distribution Name	Ubuntu
Distribution Version	20.04.2 LTS
Linux Kernel	5.4.0-72-generic
Architecture	x86_64
ZFS Version	2.1.0-rc4
SPL Version	2.1.0-rc4

Describe the problem you're observing

On hosts with dash as /bin/sh the zed_guid_to_pool() helper function in zed.d/zed-functions.sh doesn't work due to using the dash-internal printf with a format it doesn't understand.

Suggested workaround is to either use the binary printf, ie /usr/bin/printf although /bin/printf works on newer Linux distros, or to simply declare the zed.d scripts to be bash scripts with #!/bin/bash.

The latter would likely be more honest with regards to how much is actually tested with other shells, and make it easier for developers with nice features like local variables in functions etc. There's nothing wrong with stating that a script is a bash-script, it's just being honest with the dependency. But saying that a script is an sh-script opens up cans of worms since then you must really really be sh, which I know openzfs knows and tries hard to be but yet cases like this are missed despite shellcheck etc.

Describe how to reproduce the problem

# /bin/dash
# . /etc/zfs/zed.d/zed-functions.sh
# zed_guid_to_pool $(zpool list -Ho guid | head -n 1)
/bin/dash: 514: printf: %l: invalid directive

Include any warning/errors/backtraces from the system logs

[nabijaczleweli]

Added this to #11935