Add another new sysctl in support of the forthcoming procstat(1) to

support its -k argument:

kern.proc.kstack - dump the kernel stack of a process, if debugging
  is permitted.

This sysctl is present if either "options DDB" or "options STACK" is
compiled into the kernel.  Having support for tracing the kernel
stacks of processes from user space makes it much easier to debug
(or understand) specific wmesg's while avoiding the need to enter
DDB in order to determine the path by which a process came to be
blocked on a particular wait channel or lock.

1 files changed, 19 insertions, 0 deletions

diff --git a/sys/sys/user.h b/sys/sys/user.h
index 9e4f14f163cf..92203f07539e 100644
--- a/sys/sys/user.h
+++ b/sys/sys/user.h
@@ -319,4 +319,23 @@ struct kinfo_vmentry {
 	int	 _kve_ispare[8];		/* Space for more stuff. */
 };
 
+/*
+ * The KERN_PROC_KSTACK sysctl allows a process to dump the kernel stacks of
+ * another process as a series of entries.  Each stack is represented by a
+ * series of symbol names and offsets as generated by stack_sbuf_print(9).
+ */
+#define	KKST_MAXLEN	1024
+
+#define	KKST_STATE_STACKOK	0		/* Stack is valid. */
+#define	KKST_STATE_SWAPPED	1		/* Stack swapped out. */
+#define	KKST_STATE_RUNNING	2		/* Stack ephemeral. */
+
+struct kinfo_kstack {
+	lwpid_t	 kkst_tid;			/* ID of thread. */
+	int	 kkst_state;			/* Validity of stack. */
+	char	 kkst_trace[KKST_MAXLEN];	/* String representing stack. */
+	void	*_kkst_pspare[8];		/* Space for more stuff. */
+	int	 _kkst_ispare[8];		/* Space for more stuff. */
+};
+
 #endif