Re: mmap cdev function in device drivers

[Peter Edwards]

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 [EMAIL PROTECTED] with "unsubscribe freebsd-hackers" in the body of the message