Hello Olivier
On 10/16/18 9:37 PM, Olivier Gayot wrote:
> Since glibc 2.24, the use of posix_spawn (2) makes an unconditional call
> to clone(CLONE_VM | CLONE_VFORK ...) rather than relying on fork (2) or
> vfork (2).
>
> As a consequence, the statements regarding the use of the flag
> POSIX_SPAWN_USEVFORK and how the function decides whether it should use
> fork (2) or vfork (2) are obsolete since glibc 2.24.
>
> This patch makes a distinction in the manual page between glibc 2.24 and
> older versions.
>
> Upstream commit in glibc.git:
>
> 9ff72da471 posix: New Linux posix_spawn{p} implementation
>
> Signed-off-by: Olivier Gayot <olivier.gayot@xxxxxxxxxxx>
My apologies for the delay. This patch is now applied. Thanks for
sending it.
Adhemerval, thank you for your reviews.
Cheers,
Michael
> ---
> man3/posix_spawn.3 | 26 ++++++++++++++++++--------
> 1 file changed, 18 insertions(+), 8 deletions(-)
>
> diff --git a/man3/posix_spawn.3 b/man3/posix_spawn.3
> index 3e1e9011c..e8c0de172 100644
> --- a/man3/posix_spawn.3
> +++ b/man3/posix_spawn.3
> @@ -155,9 +155,16 @@ and the
> .BR exec ()
> step (executed in the child).
> .SS fork() step
> -The
> +Since glibc 2.24, the
> .BR posix_spawn ()
> function commences by calling
> +.BR clone (2)
> +with
> +.BR CLONE_VM
> +and
> +.BR CLONE_VFORK
> +flags.
> +Older implementations use
> .BR fork (2),
> or possibly
> .BR vfork (2)
> @@ -176,7 +183,7 @@ If the child fails in any of the housekeeping steps described below,
> or fails to execute the desired file,
> it exits with a status of 127.
> .PP
> -The child process is created using
> +Before glibc 2.24, the child process is created using
> .BR vfork (2)
> instead of
> .BR fork (2)
> @@ -480,14 +487,16 @@ The
> and
> .BR posix_spawnp ()
> functions fail only in the case where the underlying
> -.BR fork (2)
> -or
> +.BR fork (2),
> .BR vfork (2)
> +or
> +.BR clone (2)
> call fails; in these cases, these functions return an error number,
> which will be one of the errors described for
> -.BR fork (2)
> +.BR fork (2),
> +.BR vfork (2)
> or
> -.BR vfork (2).
> +.BR clone (2).
> .PP
> In addition, these functions fail if:
> .TP
> @@ -527,13 +536,14 @@ only the POSIX-specified functions.
> although these objects may be implemented as structures containing fields,
> portable programs must avoid dependence on such implementation details.)
> .PP
> -According to POSIX, it unspecified whether fork handlers established with
> +According to POSIX, it is unspecified whether fork handlers established with
> .BR pthread_atfork (3)
> are called when
> .BR posix_spawn ()
> is invoked.
> -On glibc,
> +Since glibc 2.24, the fork handlers are not executed in any case.
> .\" Tested on glibc 2.12
> +On older implementations,
> fork handlers are called only if the child is created using
> .BR fork (2).
> .PP
>
--
Michael Kerrisk
Linux man-pages maintainer; http://www.kernel.org/doc/man-pages/
Linux/UNIX System Programming Training: http://man7.org/training/
