Re: [PATCH] Add gettid and tgkill syscall wrappers.

[Rich Felker <dalias@libc.org>]

On Thu, Aug 01, 2019 at 04:31:11PM -0400, James Y Knight wrote:
> 

> From bdb4f28edece4b81e99becf4ffcdc69449211764 Mon Sep 17 00:00:00 2001
> From: James Y Knight <jyknight@google.com>
> Date: Thu, 1 Aug 2019 12:43:08 -0400
> Subject: [PATCH] Add gettid and tgkill syscall wrappers.
> 
> ---
>  include/signal.h   | 1 +
>  include/unistd.h   | 1 +
>  src/linux/gettid.c | 8 ++++++++
>  src/linux/tgkill.c | 8 ++++++++
>  4 files changed, 18 insertions(+)
>  create mode 100644 src/linux/gettid.c
>  create mode 100644 src/linux/tgkill.c
> 
> diff --git a/include/signal.h b/include/signal.h
> index 5c48cb83..6843323a 100644
> --- a/include/signal.h
> +++ b/include/signal.h
> @@ -257,6 +257,7 @@ void (*bsd_signal(int, void (*)(int)))(int);
>  int sigisemptyset(const sigset_t *);
>  int sigorset (sigset_t *, const sigset_t *, const sigset_t *);
>  int sigandset(sigset_t *, const sigset_t *, const sigset_t *);
> +int tgkill(pid_t, pid_t, int);
>  
>  #define SA_NOMASK SA_NODEFER
>  #define SA_ONESHOT SA_RESETHAND
> diff --git a/include/unistd.h b/include/unistd.h
> index 9485da7a..4764f157 100644
> --- a/include/unistd.h
> +++ b/include/unistd.h
> @@ -188,6 +188,7 @@ char *get_current_dir_name(void);
>  int syncfs(int);
>  int euidaccess(const char *, int);
>  int eaccess(const char *, int);
> +pid_t gettid(void);
>  #endif
>  
>  #if defined(_LARGEFILE64_SOURCE) || defined(_GNU_SOURCE)
> diff --git a/src/linux/gettid.c b/src/linux/gettid.c
> new file mode 100644
> index 00000000..6490101d
> --- /dev/null
> +++ b/src/linux/gettid.c
> @@ -0,0 +1,8 @@
> +#define _GNU_SOURCE
> +#include <unistd.h>
> +#include "syscall.h"
> +
> +pid_t gettid(void)
> +{
> +	return __syscall(SYS_gettid);
> +}
> diff --git a/src/linux/tgkill.c b/src/linux/tgkill.c
> new file mode 100644
> index 00000000..97365d58
> --- /dev/null
> +++ b/src/linux/tgkill.c
> @@ -0,0 +1,8 @@
> +#define _GNU_SOURCE
> +#include <signal.h>
> +#include "syscall.h"
> +
> +int tgkill(pid_t pid, pid_t tid, int sig)
> +{
> +	return syscall(SYS_tgkill, pid, tid, sig);
> +}
> -- 
> 2.22.0.770.g0f2c4a37fd-goog

Is pid_t the right type for this? Fundamentally the futex interface
imposes a requirement that tids fit in 29 bits of int. pid_t *is* int
anyway, but it's more a matter of figuring out what the right semantic
type for this is.

I also question whether tgkill should be a supported API. The idea of
being able to address threads of other processes is dubious. Before we
start adding these, I think we should think about which ones make
sense as APIs that applications can safely use.

Also, pthread_gettid_np or something like that is probably important
to being able to use any interfaces involving tids; otherwise you can
only address yourself without explicit communication with a thread to
query its tid.

Is there a list of which interfaces glibc will be adding and their
rationale?

Rich