bug#30948: [PATCH core-updates] build-system/gnu: Turn PID 1 into an “init”-style process by default.

[Maxim Cournoyer]

Hi Ludovic,

Ludovic Courtès  writes:

> Fixes .
>
> * guix/build/gnu-build-system.scm (separate-from-pid1): New procedure.
> (%standard-phases): Add it.
> * guix/build-system/gnu.scm (gnu-build): Add #:separate-from-pid1? and
> honor it.
> (gnu-cross-build): Likewise.
>
> Reported-by: Carlo Zancanaro 
> Change-Id: I6f3bc8d8186d1a571f983a38d5e3fd178ffa2678
> ---
>  guix/build-system/gnu.scm   |  4 
>  guix/build/gnu-build-system.scm | 39 -
>  2 files changed, 42 insertions(+), 1 deletion(-)
>
> Hi!
>
> This is a second attempt I’m currently testing as part of an
> initially unrelated ‘core-updates’ series:
>
>   https://issues.guix.gnu.org/67824
>
> The principle is simple: if the build process runs as PID 1, fork
> so that PID 1 does nothing but call ‘waitpid’ in a loop while the
> actual build process runs as PID 2.
>
> This is simple and robust.  The code is written in a defensive way
> as an extra phase that can be disabled.
>
> Thoughts?

I haven't yet looked at the code, but looking at the bigger picture,
wouldn't it be a useful behavior to have for Guile itself?  Perhaps not,
as there already exists a Guile init manager (GNU Shepherd), but if it's
something relatively simple/compact to implement, perhaps it could find
its place in Guile itself, just like Bash implements correctly signal
handling when used as a PID 1 (if I'm not mistaken).

-- 
Thanks,
Maxim

bug#30948: [PATCH core-updates] build-system/gnu: Turn PID 1 into an “init”-style process by default.

[Ludovic Courtès]

Fixes .

* guix/build/gnu-build-system.scm (separate-from-pid1): New procedure.
(%standard-phases): Add it.
* guix/build-system/gnu.scm (gnu-build): Add #:separate-from-pid1? and
honor it.
(gnu-cross-build): Likewise.

Reported-by: Carlo Zancanaro 
Change-Id: I6f3bc8d8186d1a571f983a38d5e3fd178ffa2678
---
 guix/build-system/gnu.scm   |  4 
 guix/build/gnu-build-system.scm | 39 -
 2 files changed, 42 insertions(+), 1 deletion(-)

Hi!

This is a second attempt I’m currently testing as part of an
initially unrelated ‘core-updates’ series:

  https://issues.guix.gnu.org/67824

The principle is simple: if the build process runs as PID 1, fork
so that PID 1 does nothing but call ‘waitpid’ in a loop while the
actual build process runs as PID 2.

This is simple and robust.  The code is written in a defensive way
as an extra phase that can be disabled.

Thoughts?

Ludo’.

diff --git a/guix/build-system/gnu.scm b/guix/build-system/gnu.scm
index 0f886fe21d..6a89bcc0d8 100644
--- a/guix/build-system/gnu.scm
+++ b/guix/build-system/gnu.scm
@@ -362,6 +362,7 @@ (define* (gnu-build name inputs
 (license-file-regexp %license-file-regexp)
 (phases '%standard-phases)
 (locale "C.UTF-8")
+(separate-from-pid1? #t)
 (system (%current-system))
 (build (nix-system->gnu-triplet system))
 (imported-modules %default-gnu-imported-modules)
@@ -404,6 +405,7 @@ (define* (gnu-build name inputs
   (sexp->gexp phases)
   phases)
#:locale #$locale
+   #:separate-from-pid1? #$separate-from-pid1?
#:bootstrap-scripts #$bootstrap-scripts
#:configure-flags #$(if (pair? configure-flags)
(sexp->gexp configure-flags)
@@ -502,6 +504,7 @@ (define* (gnu-cross-build name
   (license-file-regexp %license-file-regexp)
   (phases '%standard-phases)
   (locale "C.UTF-8")
+  (separate-from-pid1? #t)
   (system (%current-system))
   (build (nix-system->gnu-triplet system))
   (imported-modules %default-gnu-imported-modules)
@@ -547,6 +550,7 @@ (define* (gnu-cross-build name
   (sexp->gexp phases)
   phases)
#:locale #$locale
+   #:separate-from-pid1? #$separate-from-pid1?
#:bootstrap-scripts #$bootstrap-scripts
#:configure-flags #$configure-flags
#:make-flags #$make-flags
diff --git a/guix/build/gnu-build-system.scm b/guix/build/gnu-build-system.scm
index 39707e7ace..51b8f9acbf 100644
--- a/guix/build/gnu-build-system.scm
+++ b/guix/build/gnu-build-system.scm
@@ -72,6 +72,42 @@ (define (first-subdirectory directory)
 ((first . _) first)
 (_ #f)))
 
+(define* (separate-from-pid1 #:key (separate-from-pid1? #t)
+ #:allow-other-keys)
+  "When running as PID 1 and SEPARATE-FROM-PID1? is true, run build phases as
+a child process; PID 1 then becomes responsible for reaping child processes."
+  (if separate-from-pid1?
+  (if (= 1 (getpid))
+  (dynamic-wind
+(const #t)
+(lambda ()
+  (match (primitive-fork)
+(0 #t)
+(builder-pid
+ (format (current-error-port)
+ "build process now running as PID ~a~%"
+ builder-pid)
+ (let loop ()
+   ;; Running as PID 1 so take responsibility for reaping
+   ;; child processes.
+   (match (waitpid WAIT_ANY)
+ ((pid . status)
+  (if (= pid builder-pid)
+  (if (zero? status)
+  (primitive-exit 0)
+  (begin
+(format (current-error-port)
+"build process ~a exited with status 
~a~%"
+pid status)
+(primitive-exit 1)))
+  (loop
+(const #t))
+  (format (current-error-port) "not running as PID 1 (PID: ~a)~%"
+  (getpid)))
+  (format (current-error-port)
+  "build process running as PID ~a; not forking~%"
+  (getpid
+
 (define* (set-paths #:key target inputs native-inputs
 (search-paths '()) (native-search-paths '())
 #:allow-other-keys)