Re: [PATCH] tools/run_privatens: check if it is mount point for --make-private

[Naohiro Aota <Naohiro.Aota@wdc.com>]

On Mon Mar 3, 2025 at 7:10 PM JST, Zorro Lang wrote:
> On Mon, Mar 03, 2025 at 03:42:09PM +0900, Naohiro Aota wrote:
>> While /tmp is mounted with tmpfs in the most setup, it still can be a non-mount
>> point. For example, I'm running the fstests in a container, which does not
>> mount /tmp inside the container.
>> 
>> Running any test case on such system results in having the following error
>> printed, which leads to all the test cases fail due to the output difference.
>> 
>>   mount: /tmp: not mount point or bad option.
>>          dmesg(1) may have more information after failed mount system call.
>> 
>> These lines are printed by the "mount --make-private" command. So, fix that by
>> using mountpoint command to check if the directory is a mount point or not.
>> 
>> Fixes: 247ab01fa227 ("check: run tests in a private pid/mount namespace")
>> Signed-off-by: Naohiro Aota <naohiro.aota@wdc.com>
>> ---
>>  tools/run_privatens | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>> 
>> diff --git a/tools/run_privatens b/tools/run_privatens
>> index df94974ab30c..c52e0128b8f9 100755
>> --- a/tools/run_privatens
>> +++ b/tools/run_privatens
>> @@ -8,7 +8,7 @@
>>  
>>  if [ -n "${FSTESTS_ISOL}" ]; then
>>  	for path in /proc /tmp; do
>> -		mount --make-private "$path"
>> +		mountpoint "$path" >/dev/null && mount --make-private "$path"
>
> Oh, if /tmp isn't a mountpoint on your system, don't you need to think about ...
>
>>  	done
>>  	mount -t proc proc /proc
>>  	mount -t tmpfs tmpfs /tmp
>         ^^^^^^^^^^^^^^^^^^^^^^^^^
>
> ... this step? I think the first run_privatens process will remain a "mounted"
> /tmp on your system.
>
> And then later tests will use this tmpfs. That's nearly equal to "We always
> make sure there's a tmpfs mount on /tmp at the beginning of fstests running".

That does not happen because we are already in a mount namespace created
by nsexec. The mounted "/tmp" is local to each test, and each test
showed the error above.

>
> But if we don't run that "mount tmpfs" step, I think it's not what this script
> wants (to isolate the data in /tmp). Right?

I guess we can do these instead?

mount --make-private -t proc proc /proc
mount --make-private -t tmpfs tmpfs /tmp

Actually, I'm not quite confindent that we really need "--make-private"
here. As we mount new instance of proc and tmpfs and we don't bind them,
I don't see much point making them private.

>
> Thanks,
> Zorro
>
>
>
>> -- 
>> 2.48.1
>> 
>>