[shepherd] 04/04: shepherd: Honor ‘SHEPHERD_DISABLE_SIGNALFD’ variable, for tests.

[Ludovic Courtès]

civodul pushed a commit to branch main
in repository shepherd.

commit bb0f662917d4fe5d3f5a57ca9503b48a41826451
Author: Ludovic Courtès <ludo@gnu.org>
AuthorDate: Sun Dec 24 13:02:37 2023 +0100

    shepherd: Honor ‘SHEPHERD_DISABLE_SIGNALFD’ variable, for tests.
    
    * modules/shepherd.scm (maybe-signal-port): Honor
    ‘SHEPHERD_DISABLE_SIGNALFD’.
---
 modules/shepherd.scm | 65 ++++++++++++++++++++++++++++++----------------------
 1 file changed, 38 insertions(+), 27 deletions(-)

diff --git a/modules/shepherd.scm b/modules/shepherd.scm
index 6b22b22..c99d133 100644
--- a/modules/shepherd.scm
+++ b/modules/shepherd.scm
@@ -68,34 +68,45 @@ socket file at FILE-NAME upon exit of PROC.  Return the 
values of PROC."
 (define (maybe-signal-port signals)
   "Return a signal port for SIGNALS, using 'signalfd' on GNU/Linux, or #f if
 that is not supported."
-  (catch 'system-error
-    (lambda ()
-      (let ((port (signalfd -1 signals (logior SFD_CLOEXEC SFD_NONBLOCK))))
-        ;; As per the signalfd(2) man page, block SIGNALS.  The tricky bit is
-        ;; that SIGNALS must be blocked for all the threads; new threads will
-        ;; inherit the signal mask, but we must ensure that neither Guile's
-        ;; signal delivery thread nor its finalization thread are already
-        ;; running, because if they do, they are not blocking SIGNALS.  The
-        ;; signal delivery thread is started on the first call to 'sigaction'
-        ;; so we arrange to not call 'sigaction' beforehand; as for the
-        ;; finalization thread, use 'without-automatic-finalization' to
-        ;; temporarily stop it.
-        (without-automatic-finalization
-         (let ((count (length (all-threads))))
-           (if (= 1 count)
-               (begin
-                 (block-signals signals)
-                 port)
-               (begin
-                 (local-output (l10n "warning: \
+  ;; Honor this environment variable for testing purposes: it lets us emulate
+  ;; the behavior on non-Linux systems.
+  (match (getenv "SHEPHERD_DISABLE_SIGNALFD")
+    ((or #f "0" "no")
+     (catch 'system-error
+       (lambda ()
+         (let ((port (signalfd -1 signals (logior SFD_CLOEXEC SFD_NONBLOCK))))
+           ;; As per the signalfd(2) man page, block SIGNALS.  The tricky bit 
is
+           ;; that SIGNALS must be blocked for all the threads; new threads 
will
+           ;; inherit the signal mask, but we must ensure that neither Guile's
+           ;; signal delivery thread nor its finalization thread are already
+           ;; running, because if they do, they are not blocking SIGNALS.  The
+           ;; signal delivery thread is started on the first call to 
'sigaction'
+           ;; so we arrange to not call 'sigaction' beforehand; as for the
+           ;; finalization thread, use 'without-automatic-finalization' to
+           ;; temporarily stop it.
+           (without-automatic-finalization
+            (let ((count (length (all-threads))))
+              (if (= 1 count)
+                  (begin
+                    (block-signals signals)
+                    port)
+                  (begin
+                    (local-output (l10n "warning: \
 already ~a threads running, disabling 'signalfd' support")
-                               count)
-                 (close-port port)
-                 #f))))))
-    (lambda args
-      (if (= ENOSYS (system-error-errno args))
-          #f
-          (apply throw args)))))
+                                  count)
+                    (close-port port)
+                    #f))))))
+       (lambda args
+         (if (= ENOSYS (system-error-errno args))
+             (begin
+               (local-output
+                (l10n "System lacks support for 'signalfd'; \
+using fallback mechanism."))
+               #f)
+             (apply throw args)))))
+    (_
+     (local-output (l10n "Support for 'signalfd' is disabled."))
+     #f)))
 
 (define (handle-SIGINT)
   "Handle SIGINT by stopping the Shepherd, which means rebooting if we're PID 
1."