Re: [PATCH blktests v2] nvme/068: check module reference count with patience

[John Garry <john.garry@linux.dev>]

On 8/6/26 12:30, Shin'ichiro Kawasaki wrote:
>>> +_check_nvme_core_ref_count() {
>>> +	local refcnt i
>>> +
>>> +	for ((i = 0; i < 10; i++)); do
>>> +		refcnt=$(_module_use_count nvme_core)
>>> +		if [ "$refcnt" == "" ] || [ "$refcnt" -eq "$refcnt_orig" ]; then
>> I thought that refcnt_orig was local to test(), so I am unsure how it is
>> accessible in this function...but it seems to work.
> This is a bash uniqueness. Here I quote a relevant paragraph from the Bash
> manual [*]. Some paragraphs follow and explain how bash handles local variable
> scope.
> 
>    Variables local to the function are declared with the local builtin (local
>    variables). Ordinarily, variables and their values are shared between a
>    function and its caller. These variables are visible only to the function and
>    the commands it invokes. This is particularly important when a shell function
>    calls other functions.
> 
> refcnt_orig was declared as a local variable by the caller of
> _check_nvme_core_ref_count(), then it is visible in _check_nvme_core_ref_count()
> also. I used this feature intentionally, but I understand it looks weird. If you
> like, I will update the patch to pass refcnt_orig as a function argument
> instead.
> 
> [*]https://www.gnu.org/software/bash/manual/bash.html#Shell-Functions

Understood, thanks for the info.

BTW, on another topic, it seems to be a common pattern to loop waiting 
for a condition to be true in the blktests codebase, like:

+_check_nvme_core_ref_count() {
+	local refcnt i
+
+	for ((i = 0; i < 10; i++)); do
+		refcnt=$(_module_use_count nvme_core)
+		if [ "$refcnt" == "" ] || [ "$refcnt" -eq "$refcnt_orig" ]; then
+			return 0
+		fi
+		sleep 1
+	done
+	return 1
+}

In the kernel, we have functions like wait_event_timeout(wq_head, 
condition, timeout), which calls @condition and checks the result to 
break the loop and determine success. Could it be possible to have such 
a helper in blktests? I don't know how...