linux-initrd: Check the root and other early file systems.

* gnu/system.scm (operating-system-derivation)[boot-file-systems]: Keep "/".
* gnu/system/linux-initrd.scm (file-system->spec): Keep the 'check?'
  flag.
  (qemu-initrd)[helper-packages]: New variable.  Pass it as #:to-copy.
  <gexp>: Add 'set-path-environment-variable' call.  Remove #:unionfs
  argument for 'boot-system'.
* gnu/system/vm.scm (%linux-vm-file-systems): Add 'check?' field/
  (virtualized-operating-system): Likewise for the "9p" file system.
* guix/build/linux-initrd.scm (mount-root-file-system): Change #:unionfs
  default.  Call 'check-file-system' before mounting ROOT, when
  VOLATILE-ROOT? is false.
  (check-file-system): New procedure.
  (mount-file-system): Honor 'check?' element in list; add
  'check-file-system' call.
  (boot-system): Remove #:root-fs-type and #:unionfs parameters.
  [root-mount-point?, root-fs-type]: New variables.
  Call 'mount-file-system' on all MOUNTS but "/".

gnu/system.scm

@@ -349,8 +349,10 @@ we're running in the final root."
   "Return a derivation that builds OS."
   (define boot-file-systems
     (filter (match-lambda
-             (($ <file-system> device mount-point type _ _ boot?)
+             (($ <file-system> device "/")
-              (and boot? (not (string=? mount-point "/")))))
+              #t)
+             (($ <file-system> device mount-point type flags options boot?)
+              boot?))
             (operating-system-file-systems os)))
 
   (mlet* %store-monad

gnu/system/linux-initrd.scm

@@ -198,8 +198,8 @@ a list of Guile module names to be embedded in the initrd."
   "Return a list corresponding to file-system FS that can be passed to the
 initrd code."
   (match fs
-    (($ <file-system> device mount-point type flags options)
+    (($ <file-system> device mount-point type flags options _ check?)
-     (list device mount-point type flags options))))
+     (list device mount-point type flags options check?))))
 
 (define* (qemu-initrd file-systems
                       #:key
@@ -243,24 +243,37 @@ exception and backtrace!)."
             '("fuse.ko")
             '())))
 
+  (define helper-packages
+    ;; Packages to be copied on the initrd.
+    `(,@(if (find (lambda (fs)
+                    (string-prefix? "ext" (file-system-type fs)))
+                  file-systems)
+            (list e2fsck/static)
+            '())
+      ,@(if volatile-root?
+            (list unionfs-fuse/static)
+            '())))
+
   (expression->initrd
    #~(begin
        (use-modules (guix build linux-initrd)
+                    (guix build utils)
                     (srfi srfi-26))
 
+       (with-output-to-port (%make-void-port "w")
+         (lambda ()
+           (set-path-environment-variable "PATH" '("bin" "sbin")
+                                          '#$helper-packages)))
+
        (boot-system #:mounts '#$(map file-system->spec file-systems)
                     #:linux-modules '#$linux-modules
                     #:qemu-guest-networking? #t
                     #:guile-modules-in-chroot? '#$guile-modules-in-chroot?
-                    #:unionfs (and=> #$(and volatile-root? unionfs-fuse/static)
-                                     (cut string-append <> "/bin/unionfs"))
                     #:volatile-root? '#$volatile-root?))
    #:name "qemu-initrd"
    #:modules '((guix build utils)
                (guix build linux-initrd))
-   #:to-copy (if volatile-root?
+   #:to-copy helper-packages
-                 (list unionfs-fuse/static)
-                 '())
    #:linux linux-libre
    #:linux-modules linux-modules))
 

gnu/system/vm.scm

@@ -90,13 +90,15 @@ input tuple.  The output file name is when building for SYSTEM."
           (device "store")
           (type "9p")
           (needed-for-boot? #t)
-          (options "trans=virtio"))
+          (options "trans=virtio")
+          (check? #f))
         (file-system
           (mount-point "/xchg")
           (device "xchg")
           (type "9p")
           (needed-for-boot? #t)
-          (options "trans=virtio"))))
+          (options "trans=virtio")
+          (check? #f))))
 
 (define* (expression->derivation-in-linux-vm name exp
                                              #:key
@@ -333,7 +335,8 @@ environment with the store shared with the host."
                           (device "store")
                           (type "9p")
                           (needed-for-boot? #t)
-                          (options "trans=virtio"))))))
+                          (options "trans=virtio")
+                          (check? #f))))))
 
 (define* (system-qemu-image/shared-store
           os

guix/build/linux-initrd.scm

@@ -190,7 +190,7 @@ the last argument of `mknod'."
   (+ (* major 256) minor))
 
 (define* (mount-root-file-system root type
-                                 #:key volatile-root? unionfs)
+                                 #:key volatile-root? (unionfs "unionfs"))
   "Mount the root file system of type TYPE at device ROOT.  If VOLATILE-ROOT?
 is true, mount ROOT read-only and make it a union with a writable tmpfs using
 UNIONFS."
@@ -212,20 +212,45 @@ UNIONFS."
                                     "/rw-root=RW:/real-root=RO"
                                     "/root"))
               (error "unionfs failed")))
-          (mount root "/root" type)))
+          (begin
+            (check-file-system root type)
+            (mount root "/root" type))))
     (lambda args
       (format (current-error-port) "exception while mounting '~a': ~s~%"
               root args)
       (start-repl))))
 
+(define (check-file-system device type)
+  "Run a file system check of TYPE on DEVICE."
+  (define fsck
+    (string-append "fsck." type))
+
+  (let ((status (system* fsck "-v" "-p" device)))
+    (match (status:exit-val status)
+      (0
+       #t)
+      (1
+       (format (current-error-port) "'~a' corrected errors on ~a; continuing~%"
+               fsck device))
+      (2
+       (format (current-error-port) "'~a' corrected errors on ~a; rebooting~%"
+               fsck device)
+       (sleep 3)
+       (reboot))
+      (code
+       (format (current-error-port) "'~a' exited with code ~a on ~a; spawning REPL~%"
+               fsck code device)
+       (start-repl)))))
+
 (define* (mount-file-system spec #:key (root "/root"))
   "Mount the file system described by SPEC under ROOT.  SPEC must have the
 form:
 
-  (DEVICE MOUNT-POINT TYPE (FLAGS ...) OPTIONS)
+  (DEVICE MOUNT-POINT TYPE (FLAGS ...) OPTIONS CHECK?)
 
 DEVICE, MOUNT-POINT, and TYPE must be strings; OPTIONS can be a string or #f;
-FLAGS must be a list of symbols."
+FLAGS must be a list of symbols.  CHECK? is a Boolean indicating whether to
+run a file system check."
   (define flags->bit-mask
     (match-lambda
      (('read-only rest ...)
@@ -236,8 +261,10 @@ FLAGS must be a list of symbols."
       0)))
 
   (match spec
-    ((source mount-point type (flags ...) options)
+    ((source mount-point type (flags ...) options check?)
      (let ((mount-point (string-append root "/" mount-point)))
+       (when check?
+         (check-file-system source type))
        (mkdir-p mount-point)
        (mount source mount-point type (flags->bit-mask flags)
               (if options
@@ -248,8 +275,7 @@ FLAGS must be a list of symbols."
                       (linux-modules '())
                       qemu-guest-networking?
                       guile-modules-in-chroot?
-                      volatile-root? unionfs
+                      volatile-root?
-                      (root-fs-type "ext4")
                       (mounts '()))
   "This procedure is meant to be called from an initrd.  Boot a system by
 first loading LINUX-MODULES, then setting up QEMU guest networking if
@@ -257,8 +283,8 @@ QEMU-GUEST-NETWORKING? is true, mounting the file systems specified in MOUNTS,
 and finally booting into the new root if any.  The initrd supports kernel
 command-line options '--load', '--root', and '--repl'.
 
-Mount the root file system, of type ROOT-FS-TYPE, specified by the '--root'
+Mount the root file system, specified by the '--root' command-line argument,
-command-line argument, if any.
+if any.
 
 MOUNTS must be a list suitable for 'mount-file-system'.
 
@@ -276,6 +302,18 @@ to it are lost."
             (resolve (string-append "/root" target)))
           file)))
 
+  (define root-mount-point?
+    (match-lambda
+     ((device "/" _ ...) #t)
+     (_ #f)))
+
+  (define root-fs-type
+    (or (any (match-lambda
+              ((device "/" type _ ...) type)
+              (_ #f))
+             mounts)
+        "ext4"))
+
   (display "Welcome, this is GNU's early boot Guile.\n")
   (display "Use '--repl' for an initrd REPL.\n\n")
 
@@ -310,8 +348,7 @@ to it are lost."
       (mkdir "/root"))
     (if root
         (mount-root-file-system root root-fs-type
-                                #:volatile-root? volatile-root?
+                                #:volatile-root? volatile-root?)
-                                #:unionfs unionfs)
         (mount "none" "/root" "tmpfs"))
 
     (mount-essential-file-systems #:root "/root")
@@ -321,7 +358,8 @@ to it are lost."
       (make-essential-device-nodes #:root "/root"))
 
     ;; Mount the specified file systems.
-    (for-each mount-file-system mounts)
+    (for-each mount-file-system
+              (remove root-mount-point? mounts))
 
     (when guile-modules-in-chroot?
       ;; Copy the directories that contain .scm and .go files so that the