Date: Sun, 18 Jun 2000 20:47:08 -0400 From: James Howard <howardjp@wam.umd.edu> To: freebsd-hackers@freebsd.org Subject: Why is this architecture dependent? Message-ID: <200006190047.UAA02830@rac9.wam.umd.edu>
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We know I ask dumb questions a lot, but this one may not be so dumb. A
friend of mine was joking about having a device called /dev/foo which
would be like /dev/zero, except it would spit out the word "foo" over and
over again. Well, we laughed about it, but today, I implemented
it. (This was cool since this was the first time I've ever hacked the
kernel and it worked right...)
Needless to say, since this is so similar to /dev/zero, I just copied the
code and modified it for foo in instead of 0s. But the file I had to
modify was sys/i386/i386/mem.c. The relevant code for this is this:
/* minor device 12 (/dev/zero) is source of nulls on read, rathole on write */
case 12:
if (uio->uio_rw == UIO_WRITE) {
c = iov->iov_len;
break;
}
if (zbuf == NULL) {
zbuf = (caddr_t)
malloc(PAGE_SIZE, M_TEMP, M_WAITOK);
bzero(zbuf, PAGE_SIZE);
}
c = min(iov->iov_len, PAGE_SIZE);
error = uiomove(zbuf, (int)c, uio);
continue;
What makes this architecture dependent?
The equivalent call from sys/alpha/alpha/mem.c is identical, except for
this comment after the first if block:
/*
* On the first call, allocate and zero a page
* of memory for use with /dev/zero.
*/
So why have this duplication? Why not implement it once and be done? Is
there some subtle difference I am not seeing?
Thanks, Jamie
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