utils: Move 'fcntl-flock' to (guix build syscalls).

* guix/utils.scm (%struct-flock, F_SETLKW, F_SETLK, F_xxLCK)
(fcntl-flock): Move to...
* guix/build/syscalls.scm: ... here.  New variables.
* guix/nar.scm: Adjust imports accordingly.
* tests/utils.scm ("fcntl-flock wait", "fcntl-flock non-blocking"): Move
to...
* tests/syscalls.scm: ... here.  New tests.
(temp-file): New variable.

1 files changed, 88 insertions, 0 deletions

diff --git a/tests/syscalls.scm b/tests/syscalls.scm
index 0b73fb4b0c..73fa8a7acf 100644
--- a/tests/syscalls.scm
+++ b/tests/syscalls.scm
@@ -29,6 +29,10 @@
 ;; Test the (guix build syscalls) module, although there's not much that can
 ;; actually be tested without being root.
 
+(define temp-file
+  (string-append "t-utils-" (number->string (getpid))))
+
+
 (test-begin "syscalls")
 
 (test-equal "mount, ENOENT"
@@ -172,6 +176,88 @@
                          (status:exit-val status))))
                (eq? #t result))))))))
 
+(false-if-exception (delete-file temp-file))
+(test-equal "fcntl-flock wait"
+  42                                              ; the child's exit status
+  (let ((file (open-file temp-file "w0b")))
+    ;; Acquire an exclusive lock.
+    (fcntl-flock file 'write-lock)
+    (match (primitive-fork)
+      (0
+       (dynamic-wind
+         (const #t)
+         (lambda ()
+           ;; Reopen FILE read-only so we can have a read lock.
+           (let ((file (open-file temp-file "r0b")))
+             ;; Wait until we can acquire the lock.
+             (fcntl-flock file 'read-lock)
+             (primitive-exit (read file)))
+           (primitive-exit 1))
+         (lambda ()
+           (primitive-exit 2))))
+      (pid
+       ;; Write garbage and wait.
+       (display "hello, world!"  file)
+       (force-output file)
+       (sleep 1)
+
+       ;; Write the real answer.
+       (seek file 0 SEEK_SET)
+       (truncate-file file 0)
+       (write 42 file)
+       (force-output file)
+
+       ;; Unlock, which should let the child continue.
+       (fcntl-flock file 'unlock)
+
+       (match (waitpid pid)
+         ((_  . status)
+          (let ((result (status:exit-val status)))
+            (close-port file)
+            result)))))))
+
+(test-equal "fcntl-flock non-blocking"
+  EAGAIN                                          ; the child's exit status
+  (match (pipe)
+    ((input . output)
+     (match (primitive-fork)
+       (0
+        (dynamic-wind
+          (const #t)
+          (lambda ()
+            (close-port output)
+
+            ;; Wait for the green light.
+            (read-char input)
+
+            ;; Open FILE read-only so we can have a read lock.
+            (let ((file (open-file temp-file "w0")))
+              (catch 'flock-error
+                (lambda ()
+                  ;; This attempt should throw EAGAIN.
+                  (fcntl-flock file 'write-lock #:wait? #f))
+                (lambda (key errno)
+                  (primitive-exit (pk 'errno errno)))))
+            (primitive-exit -1))
+          (lambda ()
+            (primitive-exit -2))))
+       (pid
+        (close-port input)
+        (let ((file (open-file temp-file "w0")))
+          ;; Acquire an exclusive lock.
+          (fcntl-flock file 'write-lock)
+
+          ;; Tell the child to continue.
+          (write 'green-light output)
+          (force-output output)
+
+          (match (waitpid pid)
+            ((_  . status)
+             (let ((result (status:exit-val status)))
+               (fcntl-flock file 'unlock)
+               (close-port file)
+               result)))))))))
+
 (test-assert "all-network-interface-names"
   (match (all-network-interface-names)
     (((? string? names) ..1)
@@ -303,3 +389,5 @@
      0))
 
 (test-end)
+
+(false-if-exception (delete-file temp-file))