syscalls: Export 'read-utmpx'.

* guix/build/syscalls.scm (read-utmpx-from-port): New procedure.
* tests/syscalls.scm ("read-utmpx, EOF")
("read-utmpx"): New tests.

1 files changed, 12 insertions, 1 deletions

diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm
index 475fc96490..b68c48a05a 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -21,6 +21,7 @@
 (define-module (guix build syscalls)
   #:use-module (system foreign)
   #:use-module (rnrs bytevectors)
+  #:autoload   (ice-9 binary-ports) (get-bytevector-n)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-9 gnu)
@@ -142,7 +143,8 @@
             utmpx-time
             utmpx-address
             login-type
-            utmpx-entries))
+            utmpx-entries
+            (read-utmpx-from-port . read-utmpx)))
 
 ;;; Commentary:
 ;;;
@@ -1598,4 +1600,13 @@ always a positive integer."
       ((? utmpx? entry)
        (loop (cons entry entries))))))
 
+(define (read-utmpx-from-port port)
+  "Read a utmpx entry from PORT.  Return either the EOF object or a utmpx
+entry."
+  (match (get-bytevector-n port sizeof-utmpx)
+    ((? eof-object? eof)
+     eof)
+    ((? bytevector? bv)
+     (read-utmpx bv))))
+
 ;;; syscalls.scm ends here