Collecting entropy from device_attach() times.

[Dag-Erling Smørgrav]

Dag-Erling Smørgrav <des at des.no> writes:
> If you give me a couple of days, I'll try to come up with a patch that
> collects and stores attach times during boot so we can gather and
> analyse real data.

Here's the patch, as a superset of Pawel's.  The output looks like this:

des at crashbox ~% sysctl -b hw.attachtimes| hexdump -C
00000000  72 61 6d 30 00 00 00 00  00 00 00 00 00 00 00 00  |ram0............|
00000010  00 00 00 00 00 00 00 00  00 00 00 00 00 01 24 53  |..............$S|
00000020  63 70 75 30 00 00 00 00  00 00 00 00 00 00 00 00  |cpu0............|
00000030  00 00 00 00 00 00 00 00  00 00 00 00 01 4d 6c cb  |.............Ml.|
00000040  63 70 75 31 00 00 00 00  00 00 00 00 00 00 00 00  |cpu1............|
00000050  00 00 00 00 00 00 00 00  00 00 00 00 01 4d da b6  |.............M..|
00000060  61 74 74 69 6d 65 72 30  00 00 00 00 00 00 00 00  |attimer0........|
00000070  00 00 00 00 00 00 00 00  00 00 00 00 04 59 70 8f  |.............Yp.|
[...]

where the first 24 bytes of each record contain the device name
(dev->nameunit) and the last eight bytes contain d(cyclecount) for
device_attach() as a big-endian uint64_t.

DES
-- 
Dag-Erling Smørgrav - des at des.no

Index: sys/dev/random/randomdev_soft.c
===================================================================
--- sys/dev/random/randomdev_soft.c	(revision 240914)
+++ sys/dev/random/randomdev_soft.c	(working copy)
@@ -303,7 +303,7 @@
 	KASSERT(origin == RANDOM_START || origin == RANDOM_WRITE ||
             origin == RANDOM_KEYBOARD || origin == RANDOM_MOUSE ||
             origin == RANDOM_NET || origin == RANDOM_INTERRUPT ||
-            origin == RANDOM_PURE,
+            origin == RANDOM_PURE || origin == RANDOM_DEVICE,
 	    ("random_harvest_internal: origin %d invalid\n", origin));
 
 	/* Lockless read to avoid lock operations if fifo is full. */
Index: sys/sys/random.h
===================================================================
--- sys/sys/random.h	(revision 240914)
+++ sys/sys/random.h	(working copy)
@@ -45,6 +45,7 @@
 	RANDOM_NET,
 	RANDOM_INTERRUPT,
 	RANDOM_PURE,
+	RANDOM_DEVICE,
 	ENTROPYSOURCE
 };
 void random_harvest(void *, u_int, u_int, u_int, enum esource);
Index: sys/kern/subr_bus.c
===================================================================
--- sys/kern/subr_bus.c	(revision 240914)
+++ sys/kern/subr_bus.c	(working copy)
@@ -31,6 +31,7 @@
 
 #include <sys/param.h>
 #include <sys/conf.h>
+#include <sys/endian.h>
 #include <sys/filio.h>
 #include <sys/lock.h>
 #include <sys/kernel.h>
@@ -44,6 +45,7 @@
 #include <sys/condvar.h>
 #include <sys/queue.h>
 #include <machine/bus.h>
+#include <sys/random.h>
 #include <sys/rman.h>
 #include <sys/selinfo.h>
 #include <sys/signalvar.h>
@@ -53,6 +55,7 @@
 #include <sys/bus.h>
 #include <sys/interrupt.h>
 
+#include <machine/cpu.h>
 #include <machine/stdarg.h>
 
 #include <vm/uma.h>
@@ -60,6 +63,16 @@
 SYSCTL_NODE(_hw, OID_AUTO, bus, CTLFLAG_RW, NULL, NULL);
 SYSCTL_NODE(, OID_AUTO, dev, CTLFLAG_RW, NULL, NULL);
 
+#define MAXNATTACHTIMES 128
+static struct attachtime {
+	char name[24];
+	uint64_t delta;
+} attachtimes[MAXNATTACHTIMES];
+static int nattachtimes;
+SYSCTL_OPAQUE(_hw, OID_AUTO, attachtimes, CTLFLAG_RD,
+    &attachtimes, sizeof(attachtimes), "S,attachtimes",
+    "time spent in device_attach()");
+
 /*
  * Used to attach drivers to devclasses.
  */
@@ -2760,8 +2773,10 @@
 int
 device_attach(device_t dev)
 {
+	uint64_t attachtime;
 	int error;
 
+	attachtime = get_cyclecount();
 	device_sysctl_init(dev);
 	if (!device_is_quiet(dev))
 		device_print_child(dev->parent, dev);
@@ -2784,6 +2799,15 @@
 		dev->state = DS_ATTACHED;
 	dev->flags &= ~DF_DONENOMATCH;
 	devadded(dev);
+	attachtime = get_cyclecount() - attachtime;
+	if (nattachtimes < MAXNATTACHTIMES) {
+		strlcpy(attachtimes[nattachtimes].name, dev->nameunit,
+		    sizeof(attachtimes[nattachtimes]));
+		attachtimes[nattachtimes].delta = htobe64(attachtime);
+		++nattachtimes;
+	}
+	random_harvest(&attachtime, sizeof(attachtime), 4, 0, RANDOM_DEVICE);
+
 	return (0);
 }