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

From: Christian Brauner <brauner@kernel.org>
To: Andrii Nakryiko <andrii@kernel.org>
Cc: linux-fsdevel@vger.kernel.org, viro@zeniv.linux.org.uk,
	 akpm@linux-foundation.org, linux-kernel@vger.kernel.org,
	bpf@vger.kernel.org,  gregkh@linuxfoundation.org,
	linux-mm@kvack.org
Subject: Re: [PATCH 0/5] ioctl()-based API to query VMAs from /proc/<pid>/maps
Date: Sat, 4 May 2024 13:24:23 +0200	[thread overview]
Message-ID: <20240504-rasch-gekrochen-3d577084beda@brauner> (raw)
In-Reply-To: <20240504003006.3303334-1-andrii@kernel.org>

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?