system: Make /run/current-system at activation time.

* gnu/system.scm (etc-directory): Change default value of #:profile.
  Change contents of SHELLS.  Use /run/current-system/profile/{s,}bin in
  BASHRC.
  (operating-system-boot-script)[%modules]: Add (guix build
  linux-initrd).  Add call to 'activate-current-system' in gexp.
  (operating-system-initrd-file, operating-system-grub.cfg): New
  procedures.
  (operating-system-derivation): Don't build grub.cfg here and remove it
  from the file union.
* gnu/system/vm.scm (qemu-image): Remove #:populate.
  (operating-system-build-gid, operating-system-default-contents):
  Remove.
  (system-qemu-image): Remove call to
  'operating-system-default-contents'.  Use 'operating-system-grub.cfg'
  to get grub.cfg.  Add GRUB.CFG to #:inputs.
  (system-qemu-image/shared-store): Likewise, but don't add GRUB.CFG to
  #:inputs.
  (system-qemu-image/shared-store-script): Pass --system kernel option.
* guix/build/activation.scm (%booted-system, %current-system): New
  variables.
  (boot-time-system, activate-current-system): New procedures.
* guix/build/install.scm (evaluate-populate-directive): Add case
  for ('directory name uid gid mode).
  (directives, populate-root-file-system): New procedures.
* guix/build/vm.scm (initialize-hard-disk): Replace calls to
  'evaluate-populate-directive' by a call to
  'populate-root-file-system'.
* gnu/services/dmd.scm (dmd-configuration-file): Use
  /run/current-system/profile/bin.
* gnu/services/xorg.scm (slim-service): Likewise.

gnu/services/dmd.scm

@@ -64,7 +64,7 @@
                    services))
 
           ;; guix-daemon 0.6 aborts if 'PATH' is undefined, so work around it.
-          (setenv "PATH" "/run/current-system/bin")
+          (setenv "PATH" "/run/current-system/profile/bin")
 
           (format #t "starting services...~%")
           (for-each start '#$(append-map service-provision services))))

gnu/services/xorg.scm

@@ -139,7 +139,7 @@ When AUTO-LOGIN? is true, log in automatically as DEFAULT-USER."
     (mlet %store-monad ((startx  (or startx (xorg-start-command)))
                         (xinitrc (xinitrc)))
       (text-file* "slim.cfg"  "
-default_path /run/current-system/bin
+default_path /run/current-system/profile/bin
 default_xserver " startx "
 xserver_arguments :0 vt7
 xauth_path " xauth "/bin/xauth

gnu/system.scm

@@ -55,6 +55,7 @@
 
             operating-system-derivation
             operating-system-profile
+            operating-system-grub.cfg
 
             <file-system>
             file-system
@@ -263,7 +264,7 @@ explicitly appear in OS."
                         (locale "C") (timezone "Europe/Paris")
                         (skeletons '())
                         (pam-services '())
-                        (profile "/var/run/current-system/profile")
+                        (profile "/run/current-system/profile")
                         (sudoers ""))
   "Return a derivation that builds the static part of the /etc directory."
   (mlet* %store-monad
@@ -273,8 +274,8 @@ explicitly appear in OS."
        (shells     (text-file "shells"            ; used by xterm and others
                               "\
 /bin/sh
-/run/current-system/bin/sh
+/run/current-system/profile/bin/sh
-/run/current-system/bin/bash\n"))
+/run/current-system/profile/bin/bash\n"))
        (issue      (text-file "issue" "
 This is an alpha preview of the GNU system.  Welcome.
 
@@ -293,8 +294,8 @@ export LC_ALL=\"" locale "\"
 export TZ=\"" timezone "\"
 export TZDIR=\"" tzdata "/share/zoneinfo\"
 
-export PATH=$HOME/.guix-profile/bin:" profile "/bin:" profile "/sbin
+export PATH=/run/setuid-programs:/run/current-system/profile/sbin
-export PATH=/run/setuid-programs:$PATH
+export PATH=$HOME/.guix-profile/bin:/run/current-system/profile/bin:$PATH
 export CPATH=$HOME/.guix-profile/include:" profile "/include
 export LIBRARY_PATH=$HOME/.guix-profile/lib:" profile "/lib
 alias ls='ls -p --color'
@@ -402,7 +403,8 @@ alias ll='ls -l'
 we're running in the final root."
   (define %modules
     '((guix build activation)
-      (guix build utils)))
+      (guix build utils)
+      (guix build linux-initrd)))
 
   (mlet* %store-monad ((services (operating-system-services os))
                        (etc      (operating-system-etc-directory os))
@@ -446,6 +448,9 @@ we're running in the final root."
                     ;; Activate setuid programs.
                     (activate-setuid-programs (list #$@setuid-progs))
 
+                    ;; Set up /run/current-system.
+                    (activate-current-system #:boot? #t)
+
                     ;; Close any remaining open file descriptors to be on the
                     ;; safe side.  This must be the very last thing we do,
                     ;; because Guile has internal FDs such as 'sleep_pipe'
@@ -466,8 +471,8 @@ we're running in the final root."
          (_ #f))
         (operating-system-file-systems os)))
 
-(define (operating-system-derivation os)
+(define (operating-system-initrd-file os)
-  "Return a derivation that builds OS."
+  "Return a gexp denoting the initrd file of OS."
   (define boot-file-systems
     (filter (match-lambda
              (($ <file-system> device "/")
@@ -476,15 +481,16 @@ we're running in the final root."
               boot?))
             (operating-system-file-systems os)))
 
+  (mlet %store-monad
+      ((initrd ((operating-system-initrd os) boot-file-systems)))
+    (return #~(string-append #$initrd "/initrd"))))
+
+(define (operating-system-grub.cfg os)
+  "Return the GRUB configuration file for OS."
   (mlet* %store-monad
-      ((profile     (operating-system-profile os))
+      ((system      (operating-system-derivation os))
-       (etc         (operating-system-etc-directory os))
-       (services    (operating-system-services os))
-       (boot        (operating-system-boot-script os))
-       (kernel  ->  (operating-system-kernel os))
-       (initrd      ((operating-system-initrd os) boot-file-systems))
-       (initrd-file -> #~(string-append #$initrd "/initrd"))
        (root-fs ->  (operating-system-root-file-system os))
+       (kernel ->   (operating-system-kernel os))
        (entries ->  (list (menu-entry
                            (label (string-append
                                    "GNU system with "
@@ -494,15 +500,25 @@ we're running in the final root."
                            (linux-arguments
                             (list (string-append "--root="
                                                  (file-system-device root-fs))
-                                  #~(string-append "--load=" #$boot)))
+                                  #~(string-append "--system=" #$system)
-                           (initrd initrd-file))))
+                                  #~(string-append "--load=" #$system
-       (grub.cfg (grub-configuration-file entries)))
+                                                   "/boot")))
+                           (initrd #~(string-append #$system "/initrd"))))))
+    (grub-configuration-file entries)))
+
+(define (operating-system-derivation os)
+  "Return a derivation that builds OS."
+  (mlet* %store-monad
+      ((profile     (operating-system-profile os))
+       (etc         (operating-system-etc-directory os))
+       (boot        (operating-system-boot-script os))
+       (kernel  ->  (operating-system-kernel os))
+       (initrd      (operating-system-initrd-file os)))
     (file-union "system"
                 `(("boot" ,#~#$boot)
                   ("kernel" ,#~#$kernel)
-                  ("initrd" ,initrd-file)
+                  ("initrd" ,initrd)
                   ("profile" ,#~#$profile)
-                  ("grub.cfg" ,#~#$grub.cfg)
                   ("etc" ,#~#$etc)))))
 
 ;;; system.scm ends here

gnu/system/vm.scm

@@ -192,7 +192,6 @@ made available under the /xchg CIFS share."
                      (file-system-type "ext4")
                      grub-configuration
                      (register-closures? #t)
-                     (populate #f)
                      (inputs '())
                      copy-inputs?)
   "Return a bootable, stand-alone QEMU image, with a root partition of type
@@ -203,12 +202,7 @@ file (GRUB-CONFIGURATION must be the name of a file in the VM.)
 INPUTS is a list of inputs (as for packages).  When COPY-INPUTS? is true, copy
 all of INPUTS into the image being built.  When REGISTER-CLOSURES? is true,
 register INPUTS in the store database of the image so that Guix can be used in
-the image.
+the image."
-
-POPULATE is a list of directives stating directories or symlinks to be created
-in the disk image partition.  It is evaluated once the image has been
-populated with INPUTS-TO-COPY.  It can be used to provide additional files,
-such as /etc files."
   (mlet %store-monad
       ((graph (sequence %store-monad (map input->name+output inputs))))
    (expression->derivation-in-linux-vm
@@ -241,8 +235,7 @@ such as /etc files."
                                   #:copy-closures? #$copy-inputs?
                                   #:register-closures? #$register-closures?
                                   #:disk-image-size #$disk-image-size
-                                  #:file-system-type #$file-system-type
+                                  #:file-system-type #$file-system-type)
-                                  #:directives '#$populate)
             (reboot))))
     #:system system
     #:make-disk-image? #t
@@ -254,39 +247,6 @@ such as /etc files."
 ;;; Stand-alone VM image.
 ;;;
 
-(define (operating-system-build-gid os)
-  "Return as a monadic value the group id for build users of OS, or #f."
-  (mlet %store-monad ((services (operating-system-services os)))
-    (return (any (lambda (service)
-                   (and (equal? '(guix-daemon)
-                                (service-provision service))
-                        (match (service-user-groups service)
-                          ((group)
-                           (user-group-id group)))))
-                 services))))
-
-(define (operating-system-default-contents os)
-  "Return a list of directives suitable for 'system-qemu-image' describing the
-basic contents of the root file system of OS."
-  (mlet* %store-monad ((os-drv    (operating-system-derivation os))
-                       (build-gid (operating-system-build-gid os))
-                       (profile   (operating-system-profile os)))
-    (return #~((directory #$(%store-prefix) 0 #$(or build-gid 0))
-               (directory "/etc")
-               (directory "/var/log")                     ; for dmd
-               (directory "/var/run/nscd")
-               (directory "/var/guix/gcroots")
-               ("/var/guix/gcroots/system" -> #$os-drv)
-               (directory "/run")
-               ("/run/current-system" -> #$profile)
-               (directory "/bin")
-               ("/bin/sh" -> "/run/current-system/bin/bash")
-               (directory "/tmp")
-               (directory "/var/guix/profiles/per-user/root" 0 0)
-
-               (directory "/root" 0 0)            ; an exception
-               (directory "/home" 0 0)))))
-
 (define* (system-qemu-image os
                             #:key
                             (file-system-type "ext4")
@@ -312,14 +272,12 @@ of the GNU system as described by OS."
                                   file-systems-to-keep)))))
     (mlet* %store-monad
         ((os-drv      (operating-system-derivation os))
-         (os-dir   -> (derivation->output-path os-drv))
+         (grub.cfg    (operating-system-grub.cfg os)))
-         (grub.cfg -> (string-append os-dir "/grub.cfg"))
-         (populate    (operating-system-default-contents os)))
       (qemu-image  #:grub-configuration grub.cfg
-                   #:populate populate
                    #:disk-image-size disk-image-size
                    #:file-system-type file-system-type
-                   #:inputs `(("system" ,os-drv))
+                   #:inputs `(("system" ,os-drv)
+                              ("grub.cfg" ,grub.cfg))
                    #:copy-inputs? #t))))
 
 (define (virtualized-operating-system os)
@@ -356,11 +314,8 @@ environment with the store shared with the host."
 with the host."
   (mlet* %store-monad
       ((os-drv      (operating-system-derivation os))
-       (os-dir   -> (derivation->output-path os-drv))
+       (grub.cfg    (operating-system-grub.cfg os)))
-       (grub.cfg -> (string-append os-dir "/grub.cfg"))
-       (populate    (operating-system-default-contents os)))
     (qemu-image #:grub-configuration grub.cfg
-                #:populate populate
                 #:disk-image-size disk-image-size
                 #:inputs `(("system" ,os-drv))
 
@@ -390,7 +345,7 @@ exec " #$qemu "/bin/qemu-system-x86_64 -enable-kvm -no-reboot -net nic,model=vir
   -kernel " #$(operating-system-kernel os) "/bzImage \
   -initrd " #$os-drv "/initrd \
 -append \"" #$(if graphic? "" "console=ttyS0 ")
-  "--load=" #$os-drv "/boot --root=/dev/vda1\" \
+  "--system=" #$os-drv " --load=" #$os-drv "/boot --root=/dev/vda1\" \
   -serial stdio \
   -drive file=" #$image
   ",if=virtio,cache=writeback,werror=report,readonly\n")

guix/build/activation.scm

@@ -18,13 +18,15 @@
 
 (define-module (guix build activation)
   #:use-module (guix build utils)
+  #:use-module (guix build linux-initrd)
   #:use-module (ice-9 ftw)
   #:use-module (ice-9 match)
   #:use-module (srfi srfi-1)
   #:use-module (srfi srfi-26)
   #:export (activate-users+groups
             activate-etc
-            activate-setuid-programs))
+            activate-setuid-programs
+            activate-current-system))
 
 ;;; Commentary:
 ;;;
@@ -195,4 +197,33 @@ numeric gid or #f."
 
   (for-each make-setuid-program programs))
 
+(define %booted-system
+  ;; The system we booted in (a symlink.)
+  "/run/booted-system")
+
+(define %current-system
+  ;; The system that is current (a symlink.)  This is not necessarily the same
+  ;; as %BOOTED-SYSTEM, for instance because we can re-build a new system
+  ;; configuration and activate it, without rebooting.
+  "/run/current-system")
+
+(define (boot-time-system)
+  "Return the '--system' argument passed on the kernel command line."
+  (find-long-option "--system" (linux-command-line)))
+
+(define* (activate-current-system #:optional (system (boot-time-system))
+                                  #:key boot?)
+  "Atomically make SYSTEM the current system.  When BOOT? is true, also make
+it the booted system."
+  (format #t "making '~a' the current system...~%" system)
+  (when boot?
+    (when (file-exists? %booted-system)
+      (delete-file %booted-system))
+    (symlink system %booted-system))
+
+  ;; Atomically make SYSTEM current.
+  (let ((new (string-append %current-system ".new")))
+    (symlink system new)
+    (rename-file new %current-system)))
+
 ;;; activation.scm ends here

guix/build/install.scm

@@ -19,9 +19,10 @@
 (define-module (guix build install)
   #:use-module (guix build utils)
   #:use-module (guix build install)
+  #:use-module (srfi srfi-26)
   #:use-module (ice-9 match)
   #:export (install-grub
-            evaluate-populate-directive
+            populate-root-file-system
             reset-timestamps
             register-closure))
 
@@ -46,6 +47,7 @@ MOUNT-POINT.  Return #t on success."
 (define (evaluate-populate-directive directive target)
   "Evaluate DIRECTIVE, an sexp describing a file or directory to create under
 directory TARGET."
+  (let loop ((directive directive))
     (match directive
       (('directory name)
        (mkdir-p (string-append target name)))
@@ -53,8 +55,36 @@ directory TARGET."
        (let ((dir (string-append target name)))
          (mkdir-p dir)
          (chown dir uid gid)))
+      (('directory name uid gid mode)
+       (loop `(directory ,name ,uid ,gid))
+       (chmod (string-append target name) mode))
       ((new '-> old)
-     (symlink old (string-append target new)))))
+       (symlink old (string-append target new))))))
+
+(define (directives store)
+  "Return a list of directives to populate the root file system that will host
+STORE."
+  `((directory ,store 0 0)
+    (directory "/etc")
+    (directory "/var/log")                          ; for dmd
+    (directory "/var/run/nscd")
+    (directory "/var/guix/gcroots")
+    (directory "/run")
+    ("/var/guix/gcroots/booted-system" -> "/run/booted-system")
+    ("/var/guix/gcroots/current-system" -> "/run/current-system")
+    (directory "/bin")
+    ("/bin/sh" -> "/run/current-system/profile/bin/bash")
+    (directory "/tmp" 0 0 #o1777)                 ; sticky bit
+    (directory "/var/guix/profiles/per-user/root" 0 0)
+
+    (directory "/root" 0 0)                       ; an exception
+    (directory "/home" 0 0)))
+
+(define (populate-root-file-system target)
+  "Make the essential non-store files and directories on TARGET.  This
+includes /etc, /var, /run, /bin/sh, etc."
+  (for-each (cut evaluate-populate-directive <> target)
+            (directives (%store-directory))))
 
 (define (reset-timestamps directory)
   "Reset the timestamps of all the files under DIRECTORY, so that they appear

guix/build/vm.scm

@@ -206,8 +206,7 @@ further populate the partition."
 
   ;; Evaluate the POPULATE directives.
   (display "populating...\n")
-  (for-each (cut evaluate-populate-directive <> target-directory)
+  (populate-root-file-system target-directory)
-            directives)
 
   (unless (install-grub grub.cfg "/dev/sda" target-directory)
     (error "failed to install GRUB"))