Date: Sun, 15 Oct 1995 21:19:03 +0200 From: Mark Murray <mark@grondar.za> To: hackers@freebsd.org Subject: Creating a /dev/random Message-ID: <199510151919.VAA23932@grumble.grondar.za>
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Hi
I am slowly hacking my way through the kernel, figuring out how to do
things. So far, I am doing OK, but with lots of help. Thanks guys!
I am building devices, /dev/random and /dev/urandom that when read give
random noise generated in and by the kernel. So far it is going pretty
well, but I have some unexplained hangs. I believe these are due to
my complete lack of knowledge of what the uiomove() function is supposed
to do.
Please have a look at my mods to mem.c (the home of /dev/null) and make
some suggestions:
Notes: 1) read_random() only returns the number of random bytes it thinks
are truly random, and should cause /dev/random to return EOF
when this "pool of entropy" is empty.
2) it is this /dev/random that dies. If I continually open/read/close
the kernel will wedge. No reboot, syscons is alive, but everything
else stops.
3) read_random_unlimited always returns the number of bytes requested,
even if they are dubious. This is central to /dev/urandom, which
I tried to model on /dev/zero (except for the return value :-])
4) /dev/urandom never seems to kill the system.
5) the kernel is 'hooked' to provide a contunual source of randomness.
(interrupts, keystrokes etc)
diff --exclude=CVS -udr sys.ORG/i386/i386/mem.c sys/i386/i386/mem.c
--- sys.ORG/i386/i386/mem.c Wed Sep 20 15:01:17 1995
+++ sys/i386/i386/mem.c Mon Oct 2 22:59:44 1995
@@ -135,6 +139,10 @@
register struct iovec *iov;
int error = 0;
caddr_t zbuf = NULL;
+#ifdef DEVRANDOM
+ caddr_t rbuf = NULL;
+ int poolsize;
+#endif
while (uio->uio_resid > 0 && error == 0) {
iov = uio->uio_iov;
@@ -190,6 +198,40 @@
return (0);
c = iov->iov_len;
break;
+
+#ifdef DEVRANDOM
+/* minor device 3 is filth generator /dev/random - rathole on write */
+ case 3:
+ if (uio->uio_rw == UIO_WRITE) {
+ c = iov->iov_len;
+ break;
+ }
+ if (rbuf == NULL) {
+ rbuf = (caddr_t)
+ malloc(CLBYTES, M_TEMP, M_WAITOK);
+ }
+ poolsize = read_random(rbuf, CLBYTES);
+ c = min(iov->iov_len, CLBYTES);
+ c = min(c, poolsize);
+ error = uiomove(rbuf, (int)c, uio);
+ continue;
+
+/* minor device 4 is dirt generator /dev/urandom - rathole on write */
+ case 4:
+ if (uio->uio_rw == UIO_WRITE) {
+ c = iov->iov_len;
+ break;
+ }
+ if (rbuf == NULL) {
+ rbuf = (caddr_t)
+ malloc(CLBYTES, M_TEMP, M_WAITOK);
+ }
+ poolsize = read_random_unlimited(rbuf, CLBYTES);
+ c = min(iov->iov_len, CLBYTES);
+ c = min(c, poolsize);
+ error = uiomove(rbuf, (int)c, uio);
+ continue;
+#endif
/* minor device 12 (/dev/zero) is source of nulls on read, rathole on write */
case 12:
--
Mark Murray
46 Harvey Rd, Claremont, Cape Town 7700, South Africa
+27 21 61-3768 GMT+0200
Finger mark@grumble.grondar.za for PGP key
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