[PATCH 1/3] xen: pvhvm: allow user to request no emulated device unplug

[Ian Campbell <ian.campbell@citrix.com>]

this allows the user to disable pvhvm and revert to emulated devices
in case of a system misconfiguration (e.g. initramfs with only
emulated drivers in it).

Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
---
 Documentation/kernel-parameters.txt |    1 +
 arch/x86/xen/platform-pci-unplug.c  |   12 ++++++++++--
 2 files changed, 11 insertions(+), 2 deletions(-)

diff --git a/Documentation/kernel-parameters.txt b/Documentation/kernel-parameters.txt
index 2c85c06..8bbe83b 100644
--- a/Documentation/kernel-parameters.txt
+++ b/Documentation/kernel-parameters.txt
@@ -2631,6 +2631,7 @@ and is between 256 and 4096 characters. It is defined in the file
 			all -- unplug all emulated devices (NICs and IDE disks)
 			ignore -- continue loading the Xen platform PCI driver even
 				if the version check failed
+			never -- do not unplug even if version check succeeds
 
 	xirc2ps_cs=	[NET,PCMCIA]
 			Format:
diff --git a/arch/x86/xen/platform-pci-unplug.c b/arch/x86/xen/platform-pci-unplug.c
index 554c002..c82ce1e 100644
--- a/arch/x86/xen/platform-pci-unplug.c
+++ b/arch/x86/xen/platform-pci-unplug.c
@@ -33,7 +33,7 @@
 int xen_platform_pci_unplug;
 EXPORT_SYMBOL_GPL(xen_platform_pci_unplug);
 #ifdef CONFIG_XEN_PVHVM
-static int xen_emul_unplug;
+static int xen_emul_unplug = -1;
 
 static int __init check_platform_magic(void)
 {
@@ -72,18 +72,23 @@ void __init xen_unplug_emulated_devices(void)
 {
 	int r;
 
+	/* user explicitly requested no unplug */
+	if (xen_emul_unplug == 0)
+		return;
 	/* check the version of the xen platform PCI device */
 	r = check_platform_magic();
 	/* If the version matches enable the Xen platform PCI driver.
 	 * Also enable the Xen platform PCI driver if the version is really old
 	 * and the user told us to ignore it. */
 	if (r && !(r == XEN_PLATFORM_ERR_MAGIC &&
+			(xen_emul_unplug != -1) &&
 			(xen_emul_unplug & XEN_UNPLUG_IGNORE)))
 		return;
 	/* Set the default value of xen_emul_unplug depending on whether or
 	 * not the Xen PV frontends and the Xen platform PCI driver have
 	 * been compiled for this kernel (modules or built-in are both OK). */
-	if (!xen_emul_unplug) {
+	if (xen_emul_unplug == -1) {
+		xen_emul_unplug = 0;
 		if (xen_must_unplug_nics()) {
 			printk(KERN_INFO "Netfront and the Xen platform PCI driver have "
 					"been compiled for this kernel: unplug emulated NICs.\n");
@@ -109,6 +114,7 @@ static int __init parse_xen_emul_unplug(char *arg)
 	char *p, *q;
 	int l;
 
+	xen_emul_unplug = 0;
 	for (p = arg; p; p = q) {
 		q = strchr(p, ',');
 		if (q) {
@@ -127,6 +133,8 @@ static int __init parse_xen_emul_unplug(char *arg)
 			xen_emul_unplug |= XEN_UNPLUG_ALL_NICS;
 		else if (!strncmp(p, "ignore", l))
 			xen_emul_unplug |= XEN_UNPLUG_IGNORE;
+		else if (!strncmp(p, "never", l))
+			/* Nothing to do. xen_emul_unplug = 0 above */;
 		else
 			printk(KERN_WARNING "unrecognised option '%s' "
 				 "in parameter 'xen_emul_unplug'\n", p);
-- 
1.5.6.5