Date: Mon, 16 Dec 1996 19:01:54 -0700 (MST) From: Terry Lambert <terry@lambert.org> To: scrappy@hub.org (Marc G. Fournier) Cc: hackers@freebsd.org Subject: Re: Almost have mmap() figured, I think... Message-ID: <199612170201.TAA07421@phaeton.artisoft.com> In-Reply-To: <Pine.NEB.3.95.961216200508.283F-100000@hub.org> from "Marc G. Fournier" at Dec 16, 96 08:20:55 pm
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> Altho I really hate to ask, I think I almost have this licked, but
> there is something I'm still missing, so the code isn't *quite* working the
> way it should.
>
> Essentially, to simplify things while I "understand it better",
> I've created n mmap()'d regions, each representing a frame. There are
> n corresponding mmap()'d regions, each of which correspond to the
> *size* of the frame. (I know, inelegant, but I can make it more
> elegant *after* I know better that which I'm doing...)
[ ... ]
> The regions are being created as:
>
> ======
> while(ii < FRAMES) {
> sprintf(framestr, "/tmp/frame-%02d", ii);
>
> /* Setup Video Stream Buffer */
> if((fd = open(framestr, O_RDWR|O_CREAT, 0666)) < 0) {
> fprintf(stderr, "cannot open %s\n", framestr);
> exit(-1);
> }
> ftruncate(fd, FRAMESIZE);
> if((frame[ii] =
> mmap(0, FRAMESIZE, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0))
> == (caddr_t) -1) {
> fprintf(stderr, "cannot mmap frame buffer #%02d\n", ii);
> exit(-1);
> }
> close(fd);
> }
Alternately:
start = mmap( 0, FRAMESIZE * FRAMES, PROT_READ|PROT_WRITE, MAP_SHARED, fd, 0));
for( i = 0; i < FRAMES; i++)
frame[i] = start + i * FRAMESIZE;
And use one file... 8-).
Also: Are you mapping in both the client and the server? Or just the server?
> The problem comes up when I try and print out the frame itself,
> using 'printf("%s\n", frame[ii]);'...the value printed out each time
> is exactly the same: <FF><D8><FF><E0>
What is the data in the frame? Maybe that's right? printf("%s", ...)
will stop printing if it hit a <FF><D8><FF><E0><00>...
> So, I'm making the assumption that either the way I'm calling, or
> using, readn() is incorrect for use with mmap()'d regions...would I be
> better off to read in the socket, then memcpy() the data, or strncpy()? Or
> is what I'm missing even more simple then that?
No; reading directly is a win.
Terry Lambert
terry@lambert.org
---
Any opinions in this posting are my own and not those of my present
or previous employers.
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