[PATCH] x86_64: Add compat_printk and sysctl to turn off compat layer warnings

Sometimes e.g. with crashme the compat layer warnings can be noisy.
Add a way to turn them off by gating all output through compat_printk
that checks a global sysctl. The default is not changed.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

arch/x86_64/ia32/sys_ia32.c

@@ -514,7 +514,7 @@ int sys32_ni_syscall(int call)
 	static char lastcomm[sizeof(me->comm)];
 
 	if (strncmp(lastcomm, me->comm, sizeof(lastcomm))) {
-		printk(KERN_INFO "IA32 syscall %d from %s not implemented\n",
+		compat_printk(KERN_INFO "IA32 syscall %d from %s not implemented\n",
 		       call, me->comm);
 		strncpy(lastcomm, me->comm, sizeof(lastcomm));
 	} 
@@ -916,7 +916,7 @@ long sys32_vm86_warning(void)
 	struct task_struct *me = current;
 	static char lastcomm[sizeof(me->comm)];
 	if (strncmp(lastcomm, me->comm, sizeof(lastcomm))) {
-		printk(KERN_INFO "%s: vm86 mode not supported on 64 bit kernel\n",
+		compat_printk(KERN_INFO "%s: vm86 mode not supported on 64 bit kernel\n",
 		       me->comm);
 		strncpy(lastcomm, me->comm, sizeof(lastcomm));
 	} 

fs/compat.c

@@ -55,6 +55,20 @@
 
 extern void sigset_from_compat(sigset_t *set, compat_sigset_t *compat);
 
+int compat_log = 1;
+
+int compat_printk(const char *fmt, ...)
+{
+	va_list ap;
+	int ret;
+	if (!compat_log)
+		return 0;
+	va_start(ap, fmt);
+	ret = vprintk(fmt, ap);
+	va_end(ap);
+	return ret;
+}
+
 /*
  * Not all architectures have sys_utime, so implement this in terms
  * of sys_utimes.
@@ -359,7 +373,7 @@ static void compat_ioctl_error(struct file *filp, unsigned int fd,
 	sprintf(buf,"'%c'", (cmd>>24) & 0x3f);
 	if (!isprint(buf[1]))
 		sprintf(buf, "%02x", buf[1]);
-	printk("ioctl32(%s:%d): Unknown cmd fd(%d) "
+	compat_printk("ioctl32(%s:%d): Unknown cmd fd(%d) "
 			"cmd(%08x){%s} arg(%08x) on %s\n",
 			current->comm, current->pid,
 			(int)fd, (unsigned int)cmd, buf,

include/linux/compat.h

@@ -226,5 +226,7 @@ static inline int compat_timespec_compare(struct compat_timespec *lhs,
 
 asmlinkage long compat_sys_adjtimex(struct compat_timex __user *utp);
 
+extern int compat_printk(const char *fmt, ...);
+
 #endif /* CONFIG_COMPAT */
 #endif /* _LINUX_COMPAT_H */

include/linux/sysctl.h

@@ -148,9 +148,11 @@ enum
 	KERN_SPIN_RETRY=70,	/* int: number of spinlock retries */
 	KERN_ACPI_VIDEO_FLAGS=71, /* int: flags for setting up video after ACPI sleep */
 	KERN_IA64_UNALIGNED=72, /* int: ia64 unaligned userland trap enable */
+	KERN_COMPAT_LOG=73,	/* int: print compat layer  messages */
 };
 
 
+
 /* CTL_VM names: */
 enum
 {

kernel/sysctl.c

@@ -73,6 +73,7 @@ extern int printk_ratelimit_burst;
 extern int pid_max_min, pid_max_max;
 extern int sysctl_drop_caches;
 extern int percpu_pagelist_fraction;
+extern int compat_log;
 
 #if defined(CONFIG_X86_LOCAL_APIC) && defined(CONFIG_X86)
 int unknown_nmi_panic;
@@ -676,6 +677,16 @@ static ctl_table kern_table[] = {
 	 	.mode		= 0644,
 		.proc_handler	= &proc_dointvec,
 	},
+#endif
+#ifdef CONFIG_COMPAT
+	{
+		.ctl_name	= KERN_COMPAT_LOG,
+		.procname	= "compat-log",
+		.data		= &compat_log,
+		.maxlen		= sizeof (int),
+	 	.mode		= 0644,
+		.proc_handler	= &proc_dointvec,
+	},
 #endif
 	{ .ctl_name = 0 }
 };