Query about UIO

[Greg KH]

On Thu, Jul 07, 2011 at 03:32:54PM +0800, bill wrote:
> Hi, Greg
> 
> I've been reading the UIO code, one place puzzled me a lot.
> May I ask one question about it?
> 
> -------------------------------------------------------------------------------
> drivers/uio/uio.c
> static int uio_find_mem_index(struct vm_area_struct *vma)
> {
>     int mi;
>     struct uio_device *idev = vma->vm_private_data;
> 
>     for (mi = 0; mi < MAX_UIO_MAPS; mi++) {
>         if (idev->info->mem[mi].size == 0)
>             return -1;
>         if (vma->vm_pgoff == mi)
>             return mi;
>     }
>     return -1;
> }
> 
> I don't get it why use vma->vm_pgoff as the index for struct uio_mem mem[MAX_UIO_MAPS],
> Suppose there are twohardware memory space, if user intends to map the 2nd mem, then
> the last parameter of mmap should be 1,
> 
> mapaddr = mmap(NULL, size, PROT_READ | PROT_WRITE, MAP_SHARED,
>                fd, 1);
> 
> Is my understanding correct?

I really don't know, sorry.

But Hans should know, Hans?