svn commit: r313350 - head/sys/kern

[Edward Tomasz Napierala]

Author: trasz
Date: Mon Feb  6 20:36:59 2017
New Revision: 313350
URL: https://svnweb.freebsd.org/changeset/base/313350

Log:
  In r290196 the root mount hold mechanism was changed to make it not wait
  for mount hold release if the root device already exists.  So, unless your
  rootdev is not on USB - ie in the usual case - the root mount won't wait
  for USB.  However, the old behaviour was sometimes used as "wait until USB
  is fully enumerated", and r290196 broke that.
  
  This commit adds vfs.root_mount_always_wait tunable, to force the kernel
  to always wait for root mount holds, even if the root is already there.
  
  Reviewed by:	kib
  MFC after:	2 weeks
  Relnotes:	yes
  Sponsored by:	DARPA, AFRL
  Differential Revision:	https://reviews.freebsd.org/D9387

Modified:
  head/sys/kern/vfs_mountroot.c

Modified: head/sys/kern/vfs_mountroot.c
==============================================================================
--- head/sys/kern/vfs_mountroot.c	Mon Feb  6 18:44:15 2017	(r313349)
+++ head/sys/kern/vfs_mountroot.c	Mon Feb  6 20:36:59 2017	(r313350)
@@ -132,6 +132,11 @@ static int root_mount_complete;
 static int root_mount_timeout = 3;
 TUNABLE_INT("vfs.mountroot.timeout", &root_mount_timeout);
 
+static int root_mount_always_wait = 0;
+SYSCTL_INT(_vfs, OID_AUTO, root_mount_always_wait, CTLFLAG_RDTUN,
+    &root_mount_always_wait, 0,
+    "Wait for root mount holds even if the root device already exists");
+
 SYSCTL_PROC(_vfs, OID_AUTO, root_mount_hold,
     CTLTYPE_STRING | CTLFLAG_RD | CTLFLAG_MPSAFE,
     NULL, 0, sysctl_vfs_root_mount_hold, "A",
@@ -961,10 +966,11 @@ vfs_mountroot_wait_if_neccessary(const c
 
 	/*
 	 * In case of ZFS and NFS we don't have a way to wait for
-	 * specific device.
+	 * specific device.  Also do the wait if the user forced that
+	 * behaviour by setting vfs.root_mount_always_wait=1.
 	 */
 	if (strcmp(fs, "zfs") == 0 || strstr(fs, "nfs") != NULL ||
-	    dev[0] == '\0') {
+	    dev[0] == '\0' || root_mount_always_wait != 0) {
 		vfs_mountroot_wait();
 		return (0);
 	}