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List:       busybox
Subject:    Re: [PATCH] ash: improve trap and jobs builtins in child shells
From:       Denys Vlasenko <vda.linux () googlemail ! com>
Date:       2023-03-31 13:53:53
Message-ID: CAK1hOcP_ryrVuB6nx85SfmQmH=K8dQBe+FVuaUTeGF7SUjD2MA () mail ! gmail ! com
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Applied, thank you.

On Thu, Mar 30, 2023 at 12:05 PM Ron Yorston <rmy@pobox.com> wrote:
>
> The trap and jobs builtins can be used to report information about
> traps and jobs.  This works when they're called from the current
> shell but in a child shell the required information is usually
> cleared.  Special hacks allow:
>
> - trap to work with command substitution;
> - jobs to work with command substitution or in a pipeline.
>
> Neither works with process substitution.
>
> - Relax the test for the trap hack so it also supports pipelines.
>
> - Pass the command to be evaluated to forkshell() in evalbackcmd()
>   so trap and jobs both work with process substitution.
>
> function                                             old     new   delta
> forkchild                                            629     640     +11
> argstr                                              1502    1496      -6
> ------------------------------------------------------------------------------
> (add/remove: 0/0 grow/shrink: 1/1 up/down: 11/-6)               Total: 5 bytes
>
> Signed-off-by: Ron Yorston <rmy@pobox.com>
> ---
>  shell/ash.c                            | 13 +++++++------
>  shell/ash_test/ash-signals/usage.right | 12 ++++++++++++
>  shell/ash_test/ash-signals/usage.tests | 12 ++++++++++++
>  3 files changed, 31 insertions(+), 6 deletions(-)
>
> diff --git a/shell/ash.c b/shell/ash.c
> index 559566b58..40b921be1 100644
> --- a/shell/ash.c
> +++ b/shell/ash.c
> @@ -5190,8 +5190,7 @@ forkchild(struct job *jp, union node *n, int mode)
>
>         closescript();
>
> -       if (mode == FORK_NOJOB          /* is it `xxx` ? */
> -        && n && n->type == NCMD        /* is it single cmd? */
> +       if (n && n->type == NCMD        /* is it single cmd? */
>         /* && n->ncmd.args->type == NARG - always true? */
>          && n->ncmd.args && strcmp(n->ncmd.args->narg.text, "trap") == 0
>          && n->ncmd.args->narg.next == NULL /* "trap" with no arguments */
> @@ -5285,10 +5284,12 @@ forkchild(struct job *jp, union node *n, int mode)
>         ) {
>                 TRACE(("Job hack\n"));
>                 /* "jobs": we do not want to clear job list for it,
> -                * instead we remove only _its_ own_ job from job list.
> +                * instead we remove only _its_ own_ job from job list
> +                * (if it has one).
>                  * This makes "jobs .... | cat" more useful.
>                  */
> -               freejob(curjob);
> +               if (jp)
> +                       freejob(curjob);
>                 return;
>         }
>  #endif
> @@ -6607,9 +6608,9 @@ evalbackcmd(union node *n, struct backcmd *result
>
>         if (pipe(pip) < 0)
>                 ash_msg_and_raise_perror("can't create pipe");
> -       /* process substitution uses NULL job/node, like openhere() */
> +       /* process substitution uses NULL job, like openhere() */
>         jp = (ctl == CTLBACKQ) ? makejob(/*n,*/ 1) : NULL;
> -       if (forkshell(jp, (ctl == CTLBACKQ) ? n : NULL, FORK_NOJOB) == 0) {
> +       if (forkshell(jp, n, FORK_NOJOB) == 0) {
>                 /* child */
>                 FORCE_INT_ON;
>                 close(pip[ip]);
> diff --git a/shell/ash_test/ash-signals/usage.right b/shell/ash_test/ash-signals/usage.right
> index c0dbd6c3c..df1ed2dd7 100644
> --- a/shell/ash_test/ash-signals/usage.right
> +++ b/shell/ash_test/ash-signals/usage.right
> @@ -6,6 +6,18 @@ trap -- 'a' INT
>  trap -- 'a' USR1
>  trap -- 'a' USR2
>  ___
> +trap -- 'a' EXIT trap -- 'a' INT trap -- 'a' USR1 trap -- 'a' USR2
> +___
> +trap -- 'a' EXIT
> +trap -- 'a' INT
> +trap -- 'a' USR1
> +trap -- 'a' USR2
> +___
> +trap -- 'a' EXIT
> +trap -- 'a' INT
> +trap -- 'a' USR1
> +trap -- 'a' USR2
> +___
>  ___
>  trap -- 'a' USR1
>  trap -- 'a' USR2
> diff --git a/shell/ash_test/ash-signals/usage.tests b/shell/ash_test/ash-signals/usage.tests
> index d29c6e74a..34e24cceb 100755
> --- a/shell/ash_test/ash-signals/usage.tests
> +++ b/shell/ash_test/ash-signals/usage.tests
> @@ -10,6 +10,18 @@ trap "a" EXIT INT USR1 USR2
>  echo ___
>  trap
>
> +# show them by command substitution
> +echo ___
> +echo $(trap)
> +
> +# show them by pipe
> +echo ___
> +trap | cat
> +
> +# show them by process substitution
> +echo ___
> +cat <(trap)
> +
>  # clear one
>  echo ___
>  trap 0 INT
> --
> 2.39.2
>
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