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From: kxn3796@hertz.njit.edu (Ken Nakata CIS stnt)
Newsgroups: comp.os.386bsd.questions
Subject: A question about mmap(2)
Summary: Why does not /dev/mem have mmap entry?
Message-ID: <1993Apr10.214339.11646@njitgw.njit.edu>
Date: 10 Apr 93 21:43:39 GMT
Sender: news@njit.edu
Organization: New Jersey Institute of Technology, Newark, N.J.
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Why does not /dev/mem have mmap entry?
Amancio Hasty wrote in comp.sys.ibm.pc.hardware on Mar. 20,
>Also, the local bus S3 805/928 cards have a nice feature that they map
>the video ram when using Linear mode to 0x7c000000 as supposed to
>0xa0000,hence, without operating system support we can not use
>linear mode in those cards. (It is upto the vga board manufacturer
>how to wire the top six bits.) However, this feature will allow
>us to map the entire video ram into memory.
It would be nice if the following code fragment works;
fd = open("/dev/mem", O_RDWR);
if (fd < 0) {
perror("xxx: can't open /dev/mem");
exit(1);
}
addr = mmap(0, 4194304L /* 4M byte */, PROT_READ | PROT_WRITE,
MAP_FILE, fd, 0x7c000000L);
if ((int)addr == -1) {
perror("xxx: can't mmap");
exit(1);
}
Do I miss any flaw with this?
Thanks in advance.
Ken Nakata
P.S. Probably I don't fully understand mmap system call.
The man page is only the document of mmap that I could find.
--
/* I apologize if there are incorrect, rude, and/or impolite expressions in
this mail or post. They are not intended. Please consider that English is a
second language for me and I don't have full understanding of certain words
or each nuance of a phrase. Thank you. -- Ken Nakata, CIS student, NJIT */