mountinfo: deprecate PidMountInfo

[kolyshkin]

Function PidMountInfo is not named correctly (it should be PID not Pid,
and we already have mountinfo in the package name so it's tautological),
and can not accept FilterFunc.

Besides, there are not too many users of this function (I was only able
to found one, see [1]) and users can switch to GetMountsFromReader.

Depreate this function. The plan is to remove it before v1.0.

[1] DataDog/datadog-agent@406d988

[thaJeztah]

wrt naming; its also worth considering to take the package name itself into account, eg

mountinfo.ForPID(pid)
mountinfo.FromPID(pid)
mountinfo.Get(filter)

(typing on my phone, so just a quick blurb)

[kolyshkin]

I didn't want to rename everything :) as we'll have to convert all users and/or deprecate stuff.
This is more about ability to use filters and PID.

But it's a good idea to make names shorter. Let me think about it.

[thaJeztah]

Containerd uses mount.PID() https://github.com/containerd/containerd/blob/master/mount/mountinfo_linux.go#L137

That said; have we checked if this function is used? ISTR in containerd it was not in use (need to double check), not sure if it's used in runc?

[kolyshkin]

One other way to proceed is to deprecate PidMountinfo, suggesting to use GetMountsFromReader with the first argument being an opened /proc/self/mountinfo. Maybe this would be the best way to go.

[kolyshkin]

have we checked if this function is used?

I think I've seen it used once but don't remember where it was :-\

For now I guess what I said above is the best way to go

[kolyshkin]

I think I've seen it used once but don't remember where it was :-\

Ah, here's the (only) user I found: DataDog/datadog-agent@406d988

[kolyshkin]

@thaJeztah I've change this PR to only deprecate PidMountInfo, no longer introducing a replacement for it. PTAL

[thaJeztah]

LGTM