linux-kernel - Re: [PATCH 0/5] ioctl()-based API to query VMAs from /proc/<pid>/maps

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Date: Sat, 4 May 2024 17:33:59 +0200
From: Greg KH <gregkh@...uxfoundation.org>
To: Christian Brauner <brauner@...nel.org>
Cc: Andrii Nakryiko <andrii@...nel.org>, linux-fsdevel@...r.kernel.org,
	viro@...iv.linux.org.uk, akpm@...ux-foundation.org,
	linux-kernel@...r.kernel.org, bpf@...r.kernel.org,
	linux-mm@...ck.org
Subject: Re: [PATCH 0/5] ioctl()-based API to query VMAs from /proc/<pid>/maps

On Sat, May 04, 2024 at 01:24:23PM +0200, Christian Brauner wrote:
> On Fri, May 03, 2024 at 05:30:01PM -0700, Andrii Nakryiko wrote:
> > Implement binary ioctl()-based interface to /proc/<pid>/maps file to allow
> > applications to query VMA information more efficiently than through textual
> > processing of /proc/<pid>/maps contents. See patch #2 for the context,
> > justification, and nuances of the API design.
> > 
> > Patch #1 is a refactoring to keep VMA name logic determination in one place.
> > Patch #2 is the meat of kernel-side API.
> > Patch #3 just syncs UAPI header (linux/fs.h) into tools/include.
> > Patch #4 adjusts BPF selftests logic that currently parses /proc/<pid>/maps to
> > optionally use this new ioctl()-based API, if supported.
> > Patch #5 implements a simple C tool to demonstrate intended efficient use (for
> > both textual and binary interfaces) and allows benchmarking them. Patch itself
> > also has performance numbers of a test based on one of the medium-sized
> > internal applications taken from production.
> 
> I don't have anything against adding a binary interface for this. But
> it's somewhat odd to do ioctls based on /proc files. I wonder if there
> isn't a more suitable place for this. prctl()? New vmstat() system call
> using a pidfd/pid as reference? ioctl() on fs/pidfs.c?

See my objection to the ioctl api in the patch review itself.

Also, as this is a new user/kernel api, it needs loads of documentation
(there was none), and probably also cc: linux-api, right?

thanks,

greg k-h