Provide a way for sysctl handlers to pre-wire their output buffer before

they grab a lock so that they don't block in SYSCTL_OUT() with the lock
being held.

2 files changed, 18 insertions, 0 deletions

diff --git a/sys/kern/kern_sysctl.c b/sys/kern/kern_sysctl.c
index 8f30fed..5472cf7 100644
--- a/sys/kern/kern_sysctl.c
+++ b/sys/kern/kern_sysctl.c
@@ -990,6 +990,23 @@ sysctl_new_user(struct sysctl_req *req, void *p, size_t l)
 	return (error);
 }
 
+/*
+ * Wire the user space destination buffer.  If set to a value greater than
+ * zero, the len parameter limits the maximum amount of wired memory.
+ *
+ * XXX - The len parameter is currently ignored due to the lack of
+ * a place to save it in the sysctl_req structure so that the matching
+ * amount of memory can be unwired in the sysctl exit code.
+ */
+void
+sysctl_wire_old_buffer(struct sysctl_req *req, size_t len)
+{
+	if (req->lock == 1 && req->oldptr && req->oldfunc == sysctl_old_user) {
+		vslock(req->oldptr, req->oldlen);
+		req->lock = 2;
+	}
+}
+
 int
 sysctl_find_oid(int *name, u_int namelen, struct sysctl_oid **noid,
     int *nindx, struct sysctl_req *req)
diff --git a/sys/sys/sysctl.h b/sys/sys/sysctl.h
index f9a7818..e0d47ae 100644
--- a/sys/sys/sysctl.h
+++ b/sys/sys/sysctl.h
@@ -595,6 +595,7 @@ int	userland_sysctl(struct thread *td, int *name, u_int namelen, void *old,
 			size_t *retval);
 int	sysctl_find_oid(int *name, u_int namelen, struct sysctl_oid **noid,
 			int *nindx, struct sysctl_req *req);
+void	sysctl_wire_old_buffer(struct sysctl_req *req, size_t len);
 
 #else	/* !_KERNEL */
 #include <sys/cdefs.h>