mike@BUCASB.BU.EDU (08/25/89)
I simulated the Sun Server bug in a short bit of code. I got
identical behavior to real thing. Eric if you are maintaining X11R3
here, please fix. A description of the bug follows in detail for the
athena people.
This concerns a bug I discovered in X11R3 Sun Server Code. The problems
concern the interactions in the initialization of a frame buffer using
/dev/bwtwo0 for an X server. The problem concerns the interaction
between the routines ../server/ddx/sun/{sunInit.c,sunBW.c}.and the fix is
described below. The bug bug was detected on a Sun386i/150 with 4MB of memory.
The routine sunOpenFrameBuffer in sunInit.c opens the appropriate
frame buffer and does a FBIOGTYPE ioctl correctly returning the frame buffer
description in the structure fbType. However, when memory is mapped
to the frame buffer in the following mmap calls reference is not made
the appropriate value returned by the ioctl telling the size of the
frame buffer , fbtype.fb_size, but the
reference is made to values defined in system include files
<sundev/bw2reg.h> in particular to BW2_FBSIZE, and BW2_FBSIZE_HIRES
indirectly referenced through sizeof(<variable>) where
<variable> is defined by a typedef in terms of the above quantities.
Although this turns out to be fine for large screen devices, for small
screen devices (namely my 386i/150's), the initial mmap of the frame
buffer returns with the error message, "Mapping BW2: No such device or
address", because the frame buffer for the small screen is
significantly smaller than the amount of memory which one is requesting to map.
The fix is to use the quantity returned by the FBIOGTYPE ioctl, fbType.fb_size
or if necessary some integral multiple in machine pages in subsequent
mmap calls.
Enclosed is a small piece of code which simulates the action of the Xsun
server. Thanks to Phil Budne (budd@bu-it.bu.edu), for help in testing
the server. This code generates the no error message on large
screen devices but fails on small screen (1024 X 768) devices.
-mike
-----------------------------test routine------------------------------
# include <stdio.h>
# include <sys/ioctl.h>
# include <sun/fbio.h>
# include <sundev/bw2reg.h>
# include <sys/types.h>
# include <sys/mman.h>
# include <fcntl.h>
# include <errno.h>
# define Error perror
typedef struct bw2
{
u_char image[BW2_FBSIZE]; /* Pixel buffer */
}
BW2, BW2Rec, *BW2Ptr;
main() {
extern caddr_t mmap();
int fd;
BW2Ptr fbptr = NULL;
struct fbtype fb;
fd = open( "/dev/fb", O_RDWR, 0 );
# define P(f) printf("f: %d\n", fb.fb_/**/f)
ioctl( fd, FBIOGTYPE, &fb );
P(type);
P(height);
P(width);
P(depth);
P(cmsize);
P(size);
fbptr = (BW2Ptr) mmap((caddr_t) 0, sizeof(BW2),
PROT_READ | PROT_WRITE,
MAP_SHARED | _MAP_NEW,
fd, (off_t) 0);
if ((int) fbptr == -1)
{
Error("mapping BW2");
(void) close(fd);
}
}
-------------------------------------------------------------------------
Michael Cohen ---- Center for Adaptive Systems
Boston University (617-353-7857)
Email: mike@bucasb.bu.edu
Smail: Michael Cohen
Center for Adaptive System
Department of Mathematics, Boston University
111 Cummington Street
Boston, Mass 02215