Re: [PATCH RFC] vfs: always log mount API fs context messages to dmesg

[Eric Sandeen <sandeen@redhat.com>]

On 2/26/24 5:27 AM, Christian Brauner wrote:
>> * systemd is currently probing with a dummy mount option which will
>>   generate noise, see
>>   https://github.com/systemd/systemd/blob/main/src/basic/mountpoint-util.c#L759
>>   i.e. - 
>>   [   10.689256] proc: Unknown parameter 'adefinitelynotexistingmountoption'
>>   [   10.801045] tmpfs: Unknown parameter 'adefinitelynotexistingmountoption'
>>   [   11.119431] proc: Unknown parameter 'adefinitelynotexistingmountoption'
>>   [   11.692032] proc: Unknown parameter 'adefinitelynotexistingmountoption'
> 
> Yeah, I remember that they want to know whether a given mount option is
> supported or not. That would potentially cause some people to pipe up
> complaining about dmesg getting spammed with this if we enable it.
> 
> Ok, so right now invalfc() is logged in the fs_context but it isn't
> logged in dmesg, right? Would it make sense to massage invalfc() so that
> it logs with error into the fs_context but with info into dmesg? This
> would avoid spamming dmesg and then we could risk turning this on to see
> whether this causes complaints.

Hm, yeah that would make sense I think - less consequential messages go only
to the fc, higher priority messages go to both fc and dmesg. (userspace
could still filter on severity for messages in the fc as desired.)

The interfaces are already a little unclear, ("what is warnf vs. warnfc?")
without reading the code, and this'd be another slightly unexpected wrinkle,
but functionally it makes sense to me. I wonder if a sysctl to set a
severity threshold for dmesg would make any sense, or if that'd be overkill.

> You know you could probably test your patch with xfstests to see if this
> causes any new test failures because dmesg contains new output. This
> doesn't disqualify the patch ofc it might just useful to get an idea how
> much noiser we are by doing this.

Good point. Ok, it sounds like there's some movement towards agreement that
at least some messages should go to dmesg. I'll dig a little deeper and come
up with a more solid & tested proposal.

Thanks,
-Eric