Add very basic support for the kernel to export a list of features. Each

feature is represented by a node in the new 'kern.features' sysctl node.
A feature is present if the corresponding node is present and evaluates to
true.

A FEATURE() wrapper macro is added which takes the sysctl node name and
a description of the feature as the sole arguments and creates a read-only
sysctl node with a value of 1.

Discussed on:	arch

1 files changed, 8 insertions, 0 deletions

diff --git a/sys/sys/sysctl.h b/sys/sys/sysctl.h
index 653dfd5..7c314e2 100644
--- a/sys/sys/sysctl.h
+++ b/sys/sys/sysctl.h
@@ -322,6 +322,13 @@ TAILQ_HEAD(sysctl_ctx_list, sysctl_ctx_entry);
 	sysctl_add_oid(ctx, parent, nbr, name, (access),			    \
 	ptr, arg, handler, fmt, __DESCR(descr))
 
+/*
+ * A macro to generate a read-only sysctl to indicate the presense of optional
+ * kernel features.
+ */
+#define	FEATURE(name, desc)						\
+	SYSCTL_INT(_kern_features, OID_AUTO, name, CTLFLAG_RD, 0, 1, desc)
+	
 #endif /* _KERNEL */
 
 /*
@@ -621,6 +628,7 @@ TAILQ_HEAD(sysctl_ctx_list, sysctl_ctx_entry);
  */
 extern struct sysctl_oid_list sysctl__children;
 SYSCTL_DECL(_kern);
+SYSCTL_DECL(_kern_features);
 SYSCTL_DECL(_kern_ipc);
 SYSCTL_DECL(_kern_proc);
 SYSCTL_DECL(_sysctl);