linux-kernel - Re: [PATCH v2 1/2] pidfd: show pids for nested pid namespaces in fdinfo

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Message-ID: <20191009172944.if5x3rpkb54zs4ry@wittgenstein>
Date:   Wed, 9 Oct 2019 19:29:46 +0200
From:   Christian Brauner <christian.brauner@...ntu.com>
To:     Christian Kellner <ckellner@...hat.com>
Cc:     linux-kernel@...r.kernel.org, linux-api@...r.kernel.org,
        Christian Kellner <christian@...lner.me>,
        Christian Brauner <christian@...uner.io>,
        Andrew Morton <akpm@...ux-foundation.org>,
        "Peter Zijlstra (Intel)" <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Michal Hocko <mhocko@...e.com>,
        Elena Reshetova <elena.reshetova@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Roman Gushchin <guro@...com>,
        Andrea Arcangeli <aarcange@...hat.com>,
        "Joel Fernandes (Google)" <joel@...lfernandes.org>,
        Al Viro <viro@...iv.linux.org.uk>,
        "Dmitry V. Levin" <ldv@...linux.org>
Subject: Re: [PATCH v2 1/2] pidfd: show pids for nested pid namespaces in
 fdinfo

On Wed, Oct 09, 2019 at 06:05:30PM +0200, Christian Kellner wrote:
> From: Christian Kellner <christian@...lner.me>
> 
> The fdinfo file for a process file descriptor already contains the
> pid of the process in the callers namespaces. Additionally, if pid
> namespaces are configured, show the process ids of the process in
> all nested namespaces in the same format as in the procfs status
> file, i.e. "NSPid:\t%d\%d...". This allows the easy identification
> of the processes in nested namespaces.
> 
> Signed-off-by: Christian Kellner <christian@...lner.me>
> ---
> 
> Changes in v2:
> - Moved into separate function to avoid multiple ifdefs as suggested
>   by Michal Hocko
> 
>  kernel/fork.c | 15 +++++++++++++++
>  1 file changed, 15 insertions(+)
> 
> diff --git a/kernel/fork.c b/kernel/fork.c
> index 5a0fd518e04e..f7a59ef046e9 100644
> --- a/kernel/fork.c
> +++ b/kernel/fork.c
> @@ -1681,12 +1681,27 @@ static int pidfd_release(struct inode *inode, struct file *file)
>  }
>  
>  #ifdef CONFIG_PROC_FS
> +static void pidfd_nspid(struct seq_file *m, struct pid *pid)

If it has to be a separate helper then please make it:

static inline void print_pidfd_nspid(struct seq_file *m, struct pid_namespace *ns, struct pid *pid)
{
#ifdef CONFIG_PID_NS
	int i;

	seq_puts(m, "\nNSpid:");
	for (i = ns->level; i <= pid->level; i++) {
		ns = pid->numbers[i].ns;
		seq_put_decimal_ull(m, "\t", pid_nr_ns(pid, ns));
	}
#endif
}

It's called nowhere else and we've already retrieved the pid_namespace
in pidfd_show_fdinfo().

> +{
> +#ifdef CONFIG_PID_NS
> +	struct pid_namespace *ns = proc_pid_ns(file_inode(m->file));
> +	int i;
> +
> +	seq_puts(m, "\nNSpid:");
> +	for (i = ns->level; i <= pid->level; i++) {
> +		ns = pid->numbers[i].ns;
> +		seq_put_decimal_ull(m, "\t", pid_nr_ns(pid, ns));
> +	}
> +#endif
> +}
> +
>  static void pidfd_show_fdinfo(struct seq_file *m, struct file *f)
>  {
>  	struct pid_namespace *ns = proc_pid_ns(file_inode(m->file));
>  	struct pid *pid = f->private_data;
>  
>  	seq_put_decimal_ull(m, "Pid:\t", pid_nr_ns(pid, ns));
> +	pidfd_nspid(m, pid);
>  	seq_putc(m, '\n');
>  }
>  #endif
> -- 
> 2.21.0
>