[PATCH v2 4/6] util.c: add pidfd_get_pid

[Dmitry V. Levin]

On Fri, May 15, 2020 at 09:18:38PM +0200, Ákos Uzonyi wrote:
> * defs.h (pidfd_get_pid): New function definition.
> * utils.c (pidfd_get_pid): New function, returns the pid of a pidfd.
> (printpidfd): Rewritten using pidfd_get_pid.
> (printfd_pid): Changed printpidfd arguments
> 
> Signed-off-by: Ákos Uzonyi <uzonyi.akos at gmail.com>
> ---
>  defs.h |  4 ++++
>  util.c | 37 +++++++++++++++++++------------------
>  2 files changed, 23 insertions(+), 18 deletions(-)
> 
> diff --git a/defs.h b/defs.h
> index 39985bbe..c0bda6ce 100644
> --- a/defs.h
> +++ b/defs.h
> @@ -1029,6 +1029,10 @@ printpath(struct tcb *, kernel_ulong_t addr);
>  # define TIMESPEC_TEXT_BUFSIZE \
>  		(sizeof(long long) * 3 * 2 + sizeof("{tv_sec=-, tv_nsec=}"))
>  
> +/**
> + * Returns the pid associated with pidfd of the process with ID pid_of_fd
> + */
> +extern pid_t pidfd_get_pid(pid_t pid_of_fd, int fd);
>  /**
>   * Print file descriptor fd owned by process with ID pid (from the PID NS
>   * of the tracer).
> diff --git a/util.c b/util.c
> index 3f562efc..4d3f77fb 100644
> --- a/util.c
> +++ b/util.c
> @@ -567,43 +567,44 @@ printdev(struct tcb *tcp, int fd, const char *path)
>  	return false;
>  }
>  
> -static bool
> -printpidfd(struct tcb *tcp, int fd, const char *path)
> +pid_t
> +pidfd_get_pid(pid_t pid_of_fd, int fd)
>  {
> -	static const char pidfd_path[] = "anon_inode:[pidfd]";
> -
> -	if (strcmp(path, pidfd_path))
> -		return false;
> -

Please keep this optimization in printpidfd,
it may save quite a few syscalls when fd is not a pidfd.


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