[Xen-devel] [PATCH v2 for-4.12] xen/cmdline: Work around some specific command line warnings

[Andrew Cooper <andrew.cooper3@xxxxxxxxxx>]

Xen will warn when an unknown parameter is found in the command line.  e.g.

  (d8) [ 1556.334664] (XEN) parameter "pv-shim" unknown!

One case where this goes wrong is a workaround for an old grub bug, which
resulted in "placeholder" being prepended to the command line.

Another case is when booting a CONFIG_PV_SHIM_EXCLUSIVE build, in which the
parsing for the "pv-shim" parameter is discarded.

Introduce ignore_param() and OPT_IGNORE to cope with known cases, where
warning the user is the wrong course of action to take.

Signed-off-by: Andrew Cooper <andrew.cooper3@xxxxxxxxxx>
---
CC: Jan Beulich <JBeulich@xxxxxxxx>
CC: Wei Liu <wei.liu2@xxxxxxxxxx>
CC: Roger Pau Monné <roger.pau@xxxxxxxxxx>
CC: Juergen Gross <jgross@xxxxxxxx>

v2:
 * Rewrite from scratch, following Juergen's suggestion

An implementation detail of ignore_param() is that it can only be used once
per translation unit, which is fine for now.  Two options to fix this are to
tokenise __LINE__ in (requires some extreme preprocessor magic to make work,
as ## inhibits expansion, and may cause livepatching issues), or to retain the
_val parameter and require callers to just pass in a unique string.

Thoughts welcome.
---
 xen/arch/x86/pv/shim.c | 5 ++++-
 xen/arch/x86/setup.c   | 6 ++++++
 xen/common/kernel.c    | 2 ++
 xen/include/xen/init.h | 8 +++++++-
 4 files changed, 19 insertions(+), 2 deletions(-)

diff --git a/xen/arch/x86/pv/shim.c b/xen/arch/x86/pv/shim.c
index 636a9d6..324ca27 100644
--- a/xen/arch/x86/pv/shim.c
+++ b/xen/arch/x86/pv/shim.c
@@ -40,7 +40,10 @@
 #undef virt_to_mfn
 #define virt_to_mfn(va) _mfn(__virt_to_mfn(va))
 
-#ifndef CONFIG_PV_SHIM_EXCLUSIVE
+#ifdef CONFIG_PV_SHIM_EXCLUSIVE
+/* Tolerate "pv-shim" being passed to a CONFIG_PV_SHIM_EXCLUSIVE hypervisor. */
+ignore_param("pv-shim");
+#else
 bool pv_shim;
 boolean_param("pv-shim", pv_shim);
 #endif
diff --git a/xen/arch/x86/setup.c b/xen/arch/x86/setup.c
index 06eb483..92da060 100644
--- a/xen/arch/x86/setup.c
+++ b/xen/arch/x86/setup.c
@@ -639,6 +639,12 @@ static void __init noreturn reinit_bsp_stack(void)
     reset_stack_and_jump(init_done);
 }
 
+/*
+ * Some scripts add "placeholder" to work around a grub error where it ate the
+ * first parameter.
+ */
+ignore_param("placeholder");
+
 static bool __init loader_is_grub2(const char *loader_name)
 {
     /* GRUB1="GNU GRUB 0.xx"; GRUB2="GRUB 1.xx" */
diff --git a/xen/common/kernel.c b/xen/common/kernel.c
index 053c31d..6125754 100644
--- a/xen/common/kernel.c
+++ b/xen/common/kernel.c
@@ -162,6 +162,8 @@ static int parse_params(const char *cmdline, const struct 
kernel_param *start,
                 }
                 rctmp = param->par.func(optval);
                 break;
+            case OPT_IGNORE:
+                break;
             default:
                 BUG();
                 break;
diff --git a/xen/include/xen/init.h b/xen/include/xen/init.h
index c6b453a..9384914 100644
--- a/xen/include/xen/init.h
+++ b/xen/include/xen/init.h
@@ -81,7 +81,8 @@ struct kernel_param {
         OPT_UINT,
         OPT_BOOL,
         OPT_SIZE,
-        OPT_CUSTOM
+        OPT_CUSTOM,
+        OPT_IGNORE,
     } type;
     unsigned int len;
     union {
@@ -136,6 +137,11 @@ extern const struct kernel_param __param_start[], 
__param_end[];
           .type = OPT_STR, \
           .len = sizeof(_var), \
           .par.var = &_var }
+#define ignore_param(_name)                 \
+    __setup_str __setup_str_ign[] = _name;  \
+    __kparam __setup_ign =                  \
+        { .name = __setup_str_ign,          \
+          .type = OPT_IGNORE }
 
 #define __rtparam         __param(__dataparam)
 
-- 
2.1.4


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