Improve INCLUDE_CONFIG_FILE support.

This change will let us to have full configuration of a running kernel
available in sysctl:

	sysctl -b kern.conftxt

The same configuration is also contained within the kernel image. It can be
obtained with:

	config -x <kernelfile>

Current functionality lets you to quickly recover kernel configuration, by
simply redirecting output from commands presented above and starting kernel
build procedure. "include" statements are also honored, which means options
and devices from included files are also included.

Please note that comments from configuration files are not preserved by
default. In order to preserve them, you can use -C flag for config(8). This
will bring configuration file and included files literally; however,
redirection to a file no longer works directly.

This commit was followed by discussion, that took place on freebsd-current@.
For more details, look here:

	http://lists.freebsd.org/pipermail/freebsd-current/2007-March/069994.html
	http://lists.freebsd.org/pipermail/freebsd-current/2007-May/071844.html

Development of this patch took place in Perforce, hierarchy:

	//depot/user/wkoszek/wkoszek_kconftxt/

Support from:	freebsd-current@ (links above)
Reviewed by:	imp@
Approved by:	imp@

1 files changed, 33 insertions, 0 deletions

diff --git a/sys/kern/kern_mib.c b/sys/kern/kern_mib.c
index 0a5220df3535..2ccb207c5933 100644
--- a/sys/kern/kern_mib.c
+++ b/sys/kern/kern_mib.c
@@ -42,6 +42,7 @@ __FBSDID("$FreeBSD$");
 
 #include <sys/param.h>
 #include <sys/kernel.h>
+#include <sys/sbuf.h>
 #include <sys/systm.h>
 #include <sys/sysctl.h>
 #include <sys/proc.h>
@@ -295,6 +296,38 @@ SYSCTL_PROC(_kern, KERN_SECURELVL, securelevel,
     CTLTYPE_INT|CTLFLAG_RW|CTLFLAG_PRISON, 0, 0, sysctl_kern_securelvl,
     "I", "Current secure level");
 
+/* Actual kernel configuration options. */
+extern char kernconfstring[];
+
+static int
+sysctl_kern_config(SYSCTL_HANDLER_ARGS)
+{
+	struct sbuf *sb;
+	int error;
+	char *p;
+
+	sb = sbuf_new(NULL, NULL, 2048, SBUF_AUTOEXTEND);
+	if (sb == NULL)
+		return (ENOMEM);
+	sbuf_clear(sb);
+	p = kernconfstring;
+	if (p == NULL || *p == '\0') {
+		sbuf_printf(sb, "No kernel configuration\n");
+	} else {
+		sbuf_printf(sb, "%s", p);
+	}
+	sbuf_trim(sb);
+	sbuf_putc(sb, '\n');
+	sbuf_finish(sb);
+	error = sysctl_handle_string(oidp, sbuf_data(sb), sbuf_len(sb), req);
+	if (error)
+		return (error);
+	sbuf_delete(sb);
+	return (error);
+}
+SYSCTL_PROC(_kern, OID_AUTO, conftxt, CTLTYPE_STRING|CTLFLAG_RW, 
+    0, 0, sysctl_kern_config, "", "Kernel configuration file");
+
 char domainname[MAXHOSTNAMELEN];
 SYSCTL_STRING(_kern, KERN_NISDOMAINNAME, domainname, CTLFLAG_RW,
     &domainname, sizeof(domainname), "Name of the current YP/NIS domain");