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From:   Jann Horn <jannh@google.com>
Date:   Sat, 30 Mar 2019 00:45:46 +0100
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Subject: Re: [PATCH v2 2/5] pid: add pidfd_open()
To:     Christian Brauner <christian@brauner.io>
Cc:     Andy Lutomirski <luto@kernel.org>,
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On Fri, Mar 29, 2019 at 4:54 PM Christian Brauner <christian@brauner.io> wrote:
> /* Introduction */
> This adds the pidfd_open() syscall.
> pidfd_open() allows to retrieve file descriptors for a given pid. This
> includes both file descriptors for processes and file descriptors for
> threads.

Looks good to me, overall. Apart from a few nits below:
Reviewed-by: Jann Horn <jannh@google.com>

[...]
> diff --git a/kernel/pid.c b/kernel/pid.c
> index 20881598bdfa..8c9e15e0e463 100644
> --- a/kernel/pid.c
> +++ b/kernel/pid.c
[...]
> +static struct file *pidfd_open_proc_pid(const struct file *procf, pid_t pid,
> +                                       const struct pid *pidfd_pid)
> +{
> +       char name[12]; /* int to strlen + \0 but with */

nit: comment suddenly ends at "but with"?

[...]
> +}
> +
> +static inline int pidfd_to_procfd(int procfd, struct file *pidfd_file)
> +{
> +       long fd;

nit: This should probably be an int?

[...]
> +       return fd;
> +}
[...]
> +static long pidfd_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
> +{
> +       int procfd = arg;

nit: I think it'd be semantically cleaner to move this assignment into
the switch case, but I don't feel about it strongly.

> +       switch (cmd) {
> +       case PIDFD_GET_PROCFD:
> +               return pidfd_to_procfd(procfd, file);
> +       default:
> +               return -ENOTTY;
> +       }
> +}