gnu: hurd: Support second boot.

This avoids hanging upon second boot and ensures a declarative /hurd and /dev.

* gnu/packages/patches/hurd-startup.patch: New file.
* gnu/local.mk (dist_patch_DATA): Add it.
* gnu/packages/hurd.scm (hurd): Use it.
[arguments]: In stage create-runsystem remove /dev/urandom.

Change-Id: Ifcca5562c297204735c35132820a32ca0f273677

gnu/local.mk

@@ -1545,6 +1545,7 @@ dist_patch_DATA =						\
   %D%/packages/patches/hubbub-sort-entities.patch		\
   %D%/packages/patches/hueplusplus-mbedtls.patch		\
   %D%/packages/patches/hurd-rumpdisk-no-hd.patch		\
+  %D%/packages/patches/hurd-startup.patch			\
   %D%/packages/patches/hwloc-1-test-btrfs.patch			\
   %D%/packages/patches/i7z-gcc-10.patch				\
   %D%/packages/patches/icecat-makeicecat.patch			\

gnu/packages/hurd.scm

@@ -317,7 +317,8 @@ (define-public hurd
     (name "hurd")
     (source (origin
               (inherit (package-source hurd-headers))
-              (patches (search-patches "hurd-rumpdisk-no-hd.patch"))))
+              (patches (search-patches "hurd-rumpdisk-no-hd.patch"
+                                       "hurd-startup.patch"))))
     (version (package-version hurd-headers))
     (arguments
      `(#:tests? #f                      ;no "check" target
@@ -388,6 +389,9 @@ (define-public hurd
 # Note: this /hurd/ gets substituted
 settrans --create /servers/socket/1 /hurd/pflocal
 
+# Upon second boot, (file-exists? /dev/null) in hurd-boot-system hangs unless:
+rm -f /dev/urandom
+
 # parse multiboot arguments
 for i in \"$@\"; do
     case $i in

gnu/packages/patches/hurd-startup.patch

@@ -0,0 +1,82 @@
+This avoids hanging upon second boot and ensures a declarative /dev.
+
+Upstream status: Not presented upstream.
+
+From a15d281ea012ee360c45376e964d35f6292ac549 Mon Sep 17 00:00:00 2001
+From: Janneke Nieuwenhuizen <janneke@gnu.org>
+Date: Sat, 27 May 2023 17:28:22 +0200
+Subject: [PATCH] startup: Remove /hurd, /dev, create /servers.
+
+This avoids hanging upon second boot and ensures a declarative /hurd
+and /dev.
+
+* startup/startup.c (rm_r, create_servers): New functions.
+(main): Use them to remove /dev and create /servers.  Remove /hurd
+symlink.
+---
+ startup/startup.c | 42 ++++++++++++++++++++++++++++++++++++++++++
+ 1 file changed, 42 insertions(+)
+
+diff --git a/startup/startup.c b/startup/startup.c
+index feb7d265..5f380194 100644
+--- a/startup/startup.c
++++ b/startup/startup.c
+@@ -732,6 +732,42 @@ parse_opt (int key, char *arg, struct argp_state *state)
+   return 0;
+ }
+ 
++#include <ftw.h>
++static int
++rm_r (char const *file_name)
++{
++  int callback (char const *file_name, struct stat64 const *stat_buffer,
++                int type_flag, struct FTW *ftw_buffer)
++  {
++    fprintf (stderr, "startup: removing: %s\n", file_name);
++    return remove (file_name);
++  }
++
++  return nftw64 (file_name, callback, 0, FTW_DEPTH | FTW_MOUNT | FTW_PHYS);
++}
++
++void
++create_servers (void)
++{
++  char const *servers[] = {
++    "/servers/startup",
++    "/servers/exec",
++    "/servers/proc",
++    "/servers/password",
++    "/servers/default-pager",
++    "/servers/crash-dump-core",
++    "/servers/kill",
++    "/servers/suspend",
++    0,
++  };
++  mkdir ("/servers", 0755);
++  for (char const **p = servers; *p; p++)
++    open (*p, O_WRONLY | O_APPEND | O_CREAT, 0444);
++  mkdir ("/servers/socket", 0755);
++  mkdir ("/servers/bus", 0755);
++  mkdir ("/servers/bus/pci", 0755);
++}
++
+ int
+ main (int argc, char **argv, char **envp)
+ {
+@@ -741,6 +777,12 @@ main (int argc, char **argv, char **envp)
+   mach_port_t consdev;
+   struct argp argp = { options, parse_opt, 0, doc };
+ 
++  /* GNU Guix creates fresh ones in boot-hurd-system. */
++  unlink ("/hurd");
++  rm_r ("/dev");
++  mkdir ("/dev", 0755);
++  create_servers ();
++
+   /* Parse the arguments.  We don't want the vector reordered, we
+      should pass on to our child the exact arguments we got and just
+      ignore any arguments that aren't flags for us.  ARGP_NO_ERRS
+-- 
+2.40.1
+