linux-kernel - Re: [PATCH] pidfd: add ioctl to retrieve pid info

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Message-Id: <2ab879f1-2938-4ece-a6b2-be34e4ad4c5d@app.fastmail.com>
Date: Mon, 07 Oct 2024 07:54:35 -0700
From: "Josh Triplett" <josh@...htriplett.org>
To: brauner@...nel.org
Cc: jlayton@...nel.org, josef@...icpanda.com, linux-fsdevel@...r.kernel.org,
 linux-kernel@...r.kernel.org, luca.boccassi@...il.com, oleg@...hat.com,
 paul@...l-moore.com
Subject: Re: [PATCH] pidfd: add ioctl to retrieve pid info

Christian Brauner wrote:
> struct pidfd_info {
>	/* Let userspace request expensive stuff explictly. */
>	__u64 request_mask;
>	/* And let the kernel indicate whether it knows about it. */
>	__u64 result_mask;

I don't think it's necessary to have these two fields separate. The kernel should write to the same mask field userspace used.

In theory there could be an operation to probe for *everything* the kernel understands, but in practice with a binary structure there's little point finding out about flags you don't know the corresponding structure bits for.