Re: [Buildroot] [PATCH v4 2/2] support/testing: add runtime test for mpd

[Andreas Ziegler <br025@umbiko.net>]

Hi Thomas,

On 2026-09-05 14:17, Thomas Petazzoni wrote:
> Hello Andreas,
> 
> On Sat, Sep 05, 2026 at 06:02:53AM +0200, Andreas Ziegler wrote:
>> The test determines if mpd was started by the init system by querying
>> mpd status via the built-in protocol and evaluating the result.
>> 
>> Signed-off-by: Andreas Ziegler <br025@umbiko.net>
> 
> Thanks for this new iteration!
> 
>> new file mode 100755
>> index 0000000000..4cc6895602
>> --- /dev/null
>> +++ 
>> b/support/testing/tests/package/test_mpd/rootfs-overlay/root/test_mpd.sh
>> @@ -0,0 +1,35 @@
>> +#!/bin/sh
>> +
>> +mpd_command() {
>> +	mpd_result=""
>> +	mpd_state=""
>> +	printf "Execute %s" "$1"
>> +	while IFS= read -r line; do
>> +		case $line in
>> +			OK) 						mpd_result=$line ;;
>> +			OK\ MPD*)					mpd_protocol=${line##* } ;;
>> +			state:*)					mpd_state=${line##*: } ;;
>> +			ACK\ \[[0-9]*@[0-9]*\]*)	mpd_error=${line##*\} } ;;
>> +		esac
>> +	done <<- EOF
> 
> Why are we "hacking" a minimal mpd client here instead of adding
> mpd-mpc to the image and using it to test mpd?

Hacking? The MPD command protocol is the official way to connect to the 
MPD server: https://mpd.readthedocs.io/en/latest/protocol.html. Every 
client uses it, including mpc. I use CLI one-liners regularly for 
debugging issues and a more complete version in a Python script for 
checking libraries. Why add yet another program for checking a protocol 
output?

> 
>> +	export mpd_protocol
>> +	export mpd_state
> 
> Why does this needs to be exported?

Variable scope is not clearly defined within shells. In POSIX, all 
variable declarations are global; Busybox's ash should not know about 
scope, but tolerates 'local' definitions; bash has a basic understanding 
of scope and treats function variables as local. Since I switch shells 
often (by running scripts on different machines) I usually export 
variables in functions that need visibility in the caller. It is also a 
good reminder that the function "returns" more than one value.

> 
> Thomas
> --
> Thomas Petazzoni, co-owner and CEO, Bootlin
> Embedded Linux and Kernel engineering and training
> https://bootlin.com

Kind regards,
Andreas
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