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Re: [PATCH] [manual] Job control is no longer optional.

On Tue, May 29, 2018 at 9:15 PM Zack Weinberg <> wrote:
> The manual contains an entire @node devoted to warning people that job
> control is an optional POSIX feature and might not be implemented in
> the kernel.  Job control was made mandatory in POSIX.1-2001: compare
> <>
> with <>.
> Seventeen years later, it seems to me we do not need a warning this
> loud anymore.
> Instead there is a short note in the top-level "Job Control" node
> telling people that "old" systems might not support job control and
> there's the _POSIX_JOB_CONTROL macro if you really need it.
> OK?
>         * manual/job.texi (Job Control is Optional): Remove node, as
>         job control has not been optional in quite some time.
>         (Job Control): Mention briefly that systems older than
>         POSIX.1-2001 might not support job control.
>         (setpgid): Remove cross-reference to deleted node.
>         * manual/conf.texi (_POSIX_JOB_CONTROL): Will always be
>         defined on systems conforming to POSIX.1-2001.
> ---
>  manual/conf.texi |  2 ++
>  manual/job.texi  | 38 +++++++++-----------------------------
>  2 files changed, 11 insertions(+), 29 deletions(-)
> diff --git a/manual/conf.texi b/manual/conf.texi
> index f1dce4aa44..51fb2f5aa1 100644
> --- a/manual/conf.texi
> +++ b/manual/conf.texi
> @@ -156,6 +156,8 @@ supported; use @code{sysconf} to find out.  @xref{Sysconf}.
>  If this symbol is defined, it indicates that the system supports job
>  control.  Otherwise, the implementation behaves as if all processes
>  within a session belong to a single process group.  @xref{Job Control}.
> +Systems conforming to the 2001 revision of POSIX, or newer, will
> +always define this symbol.
>  @end deftypevr
>  @deftypevr Macro int _POSIX_SAVED_IDS
> diff --git a/manual/job.texi b/manual/job.texi
> index 944967a73d..e304313ca7 100644
> --- a/manual/job.texi
> +++ b/manual/job.texi
> @@ -19,9 +19,15 @@ You need to be familiar with concepts relating to process creation
>  Handling}) in order to understand this material presented in this
>  chapter.
> +Some old systems do not support job control, but @gnusystems{} always
> +have, and it is a required feature in the 2001 revision of POSIX.1
> +(@pxref{POSIX}).  If you need to be portable to old systems, you can
> +use the @code{_POSIX_JOB_CONTROL} macro to test at compile-time
> +whether the system supports job control.  @xref{System Options}.
> +
>  @menu
>  * Concepts of Job Control::     Jobs can be controlled by a shell.
> -* Job Control is Optional::     Not all POSIX systems support job control.
>  * Controlling Terminal::        How a process gets its controlling terminal.
>  * Access to the Terminal::      How processes share the controlling terminal.
>  * Orphaned Process Groups::     Jobs left after the user logs out.
> @@ -29,7 +35,7 @@ chapter.
>  * Functions for Job Control::   Functions to control process groups.
>  @end menu
> -@node Concepts of Job Control, Job Control is Optional,  , Job Control
> +@node Concepts of Job Control
>  @section Concepts of Job Control
>  @cindex shell
> @@ -102,30 +108,7 @@ jobs between foreground and background.
>  @xref{Access to the Terminal}, for more information about I/O to the
>  controlling terminal.
> -@node Job Control is Optional, Controlling Terminal, Concepts of Job Control , Job Control
> -@section Job Control is Optional
> -@cindex job control is optional
> -
> -Not all operating systems support job control.  @gnusystems{} do
> -support job control, but if you are using @theglibc{} on some other
> -system, that system may not support job control itself.
> -
> -You can use the @code{_POSIX_JOB_CONTROL} macro to test at compile-time
> -whether the system supports job control.  @xref{System Options}.
> -
> -If job control is not supported, then there can be only one process
> -group per session, which behaves as if it were always in the foreground.
> -The functions for creating additional process groups simply fail with
> -the error code @code{ENOSYS}.
> -
> -The macros naming the various job control signals (@pxref{Job Control
> -Signals}) are defined even if job control is not supported.  However,
> -the system never generates these signals, and attempts to send a job
> -control signal or examine or specify their actions report errors or do
> -nothing.
> -
> -
> -@node Controlling Terminal, Access to the Terminal, Job Control is Optional, Job Control
> +@node Controlling Terminal
>  @section Controlling Terminal of a Process
>  One of the attributes of a process is its controlling terminal.  Child
> @@ -1166,9 +1149,6 @@ The @code{setpgid} function puts the process @var{pid} into the process
>  group @var{pgid}.  As a special case, either @var{pid} or @var{pgid} can
>  be zero to indicate the process ID of the calling process.
> -This function fails on a system that does not support job control.
> -@xref{Job Control is Optional}, for more information.
> -
>  If the operation is successful, @code{setpgid} returns zero.  Otherwise
>  it returns @code{-1}.  The following @code{errno} error conditions are
>  defined for this function:
> --
> 2.17.0

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