Re: [PATCH v3 0/7] Statsfs: a new ram-based file system for Linux kernel statistics

From: Emanuele Giuseppe Esposito
Date: Wed May 27 2020 - 09:14:54 EST

The file system is mounted on /sys/kernel/stats and would be already used
by kvm. Statsfs was initially introduced by Paolo Bonzini [1].

What's the direct motivation for this work? Moving KVM stats out of

There's many reasons: one of these is not using debugfs for statistics, but also (and mainly) to try and have a single tool that automatically takes care and displays them, instead of leaving each subsystem "on its own".

Sure, everyone gathers and processes stats in different ways, and the aim of this tool is to hopefully be extensible enough to cover all needs.
In my experience stats belong in the API used for creating/enumerating
objects, statsfs sounds like going in the exact opposite direction -
creating a parallel structure / hierarchy for exposing stats.

I know
nothing about KVM but are you sure all the info that has to be exposed
will be stats?I don't understand, what do you mean here?

In case of networking we have the basic stats in sysfs, under the
netdevice's kobject. But since we're not using sysfs much any more
for config, new stats are added in netlink APIs. Again - same APIs
used for enumeration and config.

I don't really know a lot about the networking subsystem, and as it was pointed out in another email on patch 7 by Andrew, networking needs to atomically gather and display statistics in order to make them consistent, and currently this is not supported by stats_fs but could be added in future.

In addition, right now it won't work properly if the networking namespaces are enabled. That is another issue to take into consideration. That's also why I marked patch 7 as "not for merge"

Regarding the config, as I said the idea is to gather multiple subsystems' statistics, therefore there wouldn't be a single configuration method like in netlink.
For example in kvm there are file descriptors for configuration, and creating them requires no privilege, contrary to the network interfaces.

Thank you,