linux-kernel - Re: [PATCH] eventfd: add a uapi header for eventfd userspace APIs

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Message-ID: <20230612-erden-geier-f4a73586dc20@brauner>
Date:   Mon, 12 Jun 2023 09:29:11 +0200
From:   Christian Brauner <brauner@...nel.org>
To:     wenyang.linux@...mail.com
Cc:     Alexander Viro <viro@...iv.linux.org.uk>,
        Jens Axboe <axboe@...nel.dk>, Christoph Hellwig <hch@....de>,
        Dylan Yudaken <dylany@...com>,
        David Woodhouse <dwmw@...zon.co.uk>,
        Matthew Wilcox <willy@...radead.org>,
        Eric Biggers <ebiggers@...gle.com>,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] eventfd: add a uapi header for eventfd userspace APIs

On Mon, Jun 12, 2023 at 02:59:20AM +0800, wenyang.linux@...mail.com wrote:
> From: Wen Yang <wenyang.linux@...mail.com>
> 
> Create a uapi header include/uapi/linux/eventfd.h, move the associated
> flags to the uapi header, and include it from linux/eventfd.h.
> 
> Signed-off-by: Wen Yang <wenyang.linux@...mail.com>
> Cc: Alexander Viro <viro@...iv.linux.org.uk>
> Cc: Jens Axboe <axboe@...nel.dk>
> Cc: Christian Brauner <brauner@...nel.org>
> Cc: Christoph Hellwig <hch@....de>
> Cc: Dylan Yudaken <dylany@...com>
> Cc: David Woodhouse <dwmw@...zon.co.uk>
> Cc: Matthew Wilcox <willy@...radead.org>
> Cc: Eric Biggers <ebiggers@...gle.com>
> Cc: linux-fsdevel@...r.kernel.org
> Cc: linux-kernel@...r.kernel.org
> ---

I think the change overall makes sense but see below.

>  include/linux/eventfd.h      | 16 +---------------
>  include/uapi/linux/eventfd.h | 27 +++++++++++++++++++++++++++
>  2 files changed, 28 insertions(+), 15 deletions(-)
>  create mode 100644 include/uapi/linux/eventfd.h
> 
> diff --git a/include/linux/eventfd.h b/include/linux/eventfd.h
> index 98d31cdaca40..c8be8fa6795d 100644
> --- a/include/linux/eventfd.h
> +++ b/include/linux/eventfd.h
> @@ -9,26 +9,12 @@
>  #ifndef _LINUX_EVENTFD_H
>  #define _LINUX_EVENTFD_H
>  
> -#include <linux/fcntl.h>
>  #include <linux/wait.h>
>  #include <linux/err.h>
>  #include <linux/percpu-defs.h>
>  #include <linux/percpu.h>
>  #include <linux/sched.h>
> -
> -/*
> - * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining
> - * new flags, since they might collide with O_* ones. We want
> - * to re-use O_* flags that couldn't possibly have a meaning
> - * from eventfd, in order to leave a free define-space for
> - * shared O_* flags.
> - */
> -#define EFD_SEMAPHORE (1 << 0)
> -#define EFD_CLOEXEC O_CLOEXEC
> -#define EFD_NONBLOCK O_NONBLOCK
> -
> -#define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
> -#define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)
> +#include <uapi/linux/eventfd.h>
>  
>  struct eventfd_ctx;
>  struct file;
> diff --git a/include/uapi/linux/eventfd.h b/include/uapi/linux/eventfd.h
> new file mode 100644
> index 000000000000..02e9dcdb8d29
> --- /dev/null
> +++ b/include/uapi/linux/eventfd.h
> @@ -0,0 +1,27 @@
> +/* SPDX-License-Identifier: GPL-2.0 WITH Linux-syscall-note */
> +#ifndef _UAPI_LINUX_EVENTFD_H
> +#define _UAPI_LINUX_EVENTFD_H
> +
> +#include <linux/types.h>
> +
> +/* For O_CLOEXEC and O_NONBLOCK */
> +#include <linux/fcntl.h>
> +
> +/* For _IO helpers */
> +#include <linux/ioctl.h>

Why would you want to include that?

> +
> +/*
> + * CAREFUL: Check include/uapi/asm-generic/fcntl.h when defining
> + * new flags, since they might collide with O_* ones. We want
> + * to re-use O_* flags that couldn't possibly have a meaning
> + * from eventfd, in order to leave a free define-space for
> + * shared O_* flags.
> + */

I would leave that comment together with EFD_SHARED_FCNTL_FLAGS and
EFD_FLAGS_SET in the kernel only header.

> +#define EFD_SEMAPHORE (1 << 0)
> +#define EFD_CLOEXEC O_CLOEXEC
> +#define EFD_NONBLOCK O_NONBLOCK
> +
> +#define EFD_SHARED_FCNTL_FLAGS (O_CLOEXEC | O_NONBLOCK)
> +#define EFD_FLAGS_SET (EFD_SHARED_FCNTL_FLAGS | EFD_SEMAPHORE)

I think that doesn't belong into the uapi header and should be left in
the kernel header.

> +
> +#endif /* _UAPI_LINUX_EVENTFD_H */
> -- 
> 2.34.1
>