'Fix' for esoteric misfeature discovered while searching for another bug:

select() returns EINVAL if you try to feed it a value of FD_SETSIZE greater
that 256. You can apparently adjust this by specifying a larger value of
FD_SETSIZE when configuring your kernel. However, if you set the maximum
number of open file descriptors per process to some value greater than
the FD_SETSIZE value that select() expects, many selects() within the RPC
library code will be botched because _rpc_dtablesize() will return
invalid numbers. This is to say that it will return the upper descriptor
table size limit which can be much higher than 256. Unless select() is
prepared to expect this 'unusually' high value, it will fail. (A good
example of this can be seen with NIS enabled: if you type 'unlimit' at
the shell prompt and then run any command that does NIS calls, you'll
be bombarded with errors from clnttcp_create().)

A temporary fix for this is to clamp the value returned by _rpc_dtablesize()
at FD_SETSIZE (as defined in <sys/types.h> (256)). I suppose the Right
Thing would be to provide some mechanism for select() to dynamically
adjust itself to handle FD_SETSIZE values larger than 256, but it's a
bit late in the game for that. Hopefully 256 file descriptors will be enough
to keep RPC happy for now.

1 files changed, 16 insertions, 1 deletions

diff --git a/lib/libc/rpc/rpc_dtablesize.c b/lib/libc/rpc/rpc_dtablesize.c
index c4a2ac4..e448624 100644
--- a/lib/libc/rpc/rpc_dtablesize.c
+++ b/lib/libc/rpc/rpc_dtablesize.c
@@ -30,19 +30,34 @@
 #if defined(LIBC_SCCS) && !defined(lint)
 /*static char *sccsid = "from: @(#)rpc_dtablesize.c 1.2 87/08/11 Copyr 1987 Sun Micro";*/
 /*static char *sccsid = "from: @(#)rpc_dtablesize.c	2.1 88/07/29 4.0 RPCSRC";*/
-static char *rcsid = "$Id: rpc_dtablesize.c,v 1.1 1993/10/27 05:40:48 paul Exp $";
+static char *rcsid = "rpc_dtablesize.c,v 1.1 1994/08/07 18:36:02 wollman Exp";
 #endif
 
+#include <sys/types.h>
+
 /*
  * Cache the result of getdtablesize(), so we don't have to do an
  * expensive system call every time.
  */
+/*
+ * XXX In FreeBSD 2.x, you can have the maximum number of open file
+ * descriptors be greater than FD_SETSIZE (which us 256 by default).
+ * This can lead to many RPC functions getting back an EINVAL from
+ * select() and bombing all over the place.
+ *
+ * You can apparently get select() to handle values larger than 256
+ * by patching the kernel, but most people aren't likely to know
+ * that. Clamping this function at 256 is a kludge, but it'll have to
+ * do until select()'s descriptor table size can be adjusted dynamically.
+ */
 _rpc_dtablesize()
 {
 	static int size;
 	
 	if (size == 0) {
 		size = getdtablesize();
+		if (size > FD_SETSIZE)
+			size = FD_SETSIZE;
 	}
 	return (size);
 }