01/15: build: syscalls: Add clone syscall wrapper.

[David Thompson]

davexunit pushed a commit to branch wip-container
in repository guix.

commit f9b0c92162289af3aa87ede63eee7695e61f9e17
Author: David Thompson <address@hidden>
Date:   Sun May 31 20:26:47 2015 -0400

    build: syscalls: Add clone syscall wrapper.
    
    * guix/build/syscalls.scm (clone): New procedure.
      (CLONE_NEWNS, CLONE_NEWUTS, CLONE_NEWIPC, CLONE_NEWUSER, CLONE_NEWPID,
      CLONE_NEWNET): New variables.
---
 guix/build/syscalls.scm |   32 ++++++++++++++++++++++++++++++++
 1 files changed, 32 insertions(+), 0 deletions(-)

diff --git a/guix/build/syscalls.scm b/guix/build/syscalls.scm
index 3585bf2..3346358 100644
--- a/guix/build/syscalls.scm
+++ b/guix/build/syscalls.scm
@@ -1,5 +1,6 @@
 ;;; GNU Guix --- Functional package management for GNU
 ;;; Copyright © 2014, 2015 Ludovic Courtès <address@hidden>
+;;; Copyright © 2015 David Thompson <address@hidden>
 ;;;
 ;;; This file is part of GNU Guix.
 ;;;
@@ -37,6 +38,14 @@
             swapoff
             processes
 
+            CLONE_NEWNS
+            CLONE_NEWUTS
+            CLONE_NEWIPC
+            CLONE_NEWUSER
+            CLONE_NEWPID
+            CLONE_NEWNET
+            clone
+
             IFF_UP
             IFF_BROADCAST
             IFF_LOOPBACK
@@ -247,6 +256,29 @@ user-land process."
                     (scandir "/proc"))
         <))
 
+;; Linux clone flags, from linux/sched.h
+(define CLONE_NEWNS   #x00020000)
+(define CLONE_NEWUTS  #x04000000)
+(define CLONE_NEWIPC  #x08000000)
+(define CLONE_NEWUSER #x10000000)
+(define CLONE_NEWPID  #x20000000)
+(define CLONE_NEWNET  #x40000000)
+
+;; The libc interface to sys_clone is not useful for Scheme programs, so the
+;; low-level system call is wrapped instead.
+(define clone
+  (let* ((ptr        (dynamic-func "syscall" (dynamic-link)))
+         (proc       (pointer->procedure int ptr (list int int '*)))
+         ;; TODO: Handle all supported architectures
+         (syscall-id (match (utsname:machine (uname))
+                       ("x86_64" 56)
+                       (_        120))))
+    (lambda (flags)
+      "Create a new child process by duplicating the current parent process.
+Unlike the fork system call, clone accepts FLAGS that specify which resources
+are shared between the parent and child processes."
+      (proc syscall-id flags %null-pointer))))
+
 
 ;;;
 ;;; Packed structures.