Date: Tue, 9 May 2000 09:29:27 -0400 From: Coleman Kane <cokane@one.net> To: Poul-Henning Kamp <phk@critter.freebsd.dk> Cc: Peter Edwards <peter.edwards@openet-telecom.com>, hackers@FreeBSD.ORG, Coleman Kane <cokane@one.net> Subject: Re: mmap cdev function in device drivers Message-ID: <20000509092927.B3204@cokane.yi.org> In-Reply-To: <24302.957866284@critter.freebsd.dk>; from phk@critter.freebsd.dk on Tue, May 09, 2000 at 05:58:53AM -0400 References: <3917E087.B2477FA0@openet-telecom.com> <24302.957866284@critter.freebsd.dk>
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Poul-Henning Kamp had the audacity to say:
> A good example to look at is the pci/xrpu.c file, that driver
> barely does anything but a mmap.
>
> Poul-Henning
>
Hey, thanks. That's a great idea. I'll check that out. I've been leafing through
the rather monolithic meteor, brooktree, and even the PCI pcm code.
> In message <3917E087.B2477FA0@openet-telecom.com>, Peter Edwards writes:
> >Hi,
> >Just trying to take some of the aforementioned "magic" out of i386_btop
> >/ vtop :-)
> >
> >> return( atop(vtophys(bktr->bigbuf) + offset) );
> >
> >atop (I assume) stands for "address to page" (given a pointer, give the
> >number of the page it is in)
> >vtophys is "virtual to physical". (given a pointer in a virtual address
> >space, find out the physical address of the backing memory.)
> >
> >My understanding is that mmap(2) will allocate a portion of the calling
> >process's address space, and for each page it needs to map, will call
> >the device's mmap function, giving it the calculated offset (and the
> >protection attributes).
> >
> >The device's mmap returns the index of the physical page of the memory
> >to be inserted under the virtual addresses the process sees.
> >
> >simplified_mmap_syscall_for_device(dev_t device, size_t len, off_t
> >offset)
> >{
> > caddr_t ptr = alloc_address_space(len);
> >
> > assert(ptr % PAGESIZE == 0);
> >
> > while (len) {
> > pageno = device->mmap(offset); /* Call device's mmap */
> > map_address_to_page(ptr, pageno);
> > len -= PAGESIZE;
> > offset += PAGESIZE;
> > ptr += PAGESIZE;
> > }
> >}
> >
> >So, the call above is returning the page number (of the physical address
> >(of bktr->bigbuf)).
> >
> >Of course, My ignorance will probably be corrected in due course!
> >--
> >Peter.
> >
> >
> >To Unsubscribe: send mail to majordomo@FreeBSD.org
> >with "unsubscribe freebsd-hackers" in the body of the message
> >
>
> --
> Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
> phk@FreeBSD.ORG | TCP/IP since RFC 956
> FreeBSD coreteam member | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
>
--
Coleman Kane
President,
UC Free O.S. Users Group - http://pohl.ececs.uc.edu
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