How to get the address of the page structure from the given virtual address?

How to get the address of the page structure from the given virtual address?

[B.Vinai Kumar]

Hi List

1) I allocated 8 pages using alloc_pages(GFP_KERNEL, 3). This function
returns the pointer to the first page's page structure.
How can I get the page structure address of the remaining 7 pages?

2) There is a function page_address() which takes the page structure
as an argument and returns the virtual address of the page
 that is pointed by that page structure. Is there any method which
retrives the address of the page structure?

Thanks,
Vinai.

Re: How to get the address of the page structure from the given virtual address?

[Jonathan Corbet]

On Tue, 11 Aug 2009 20:01:41 +0530
"B.Vinai Kumar" <vinaibangala2001@gmail.com> wrote:

> 1) I allocated 8 pages using alloc_pages(GFP_KERNEL, 3). This function
> returns the pointer to the first page's page structure.
> How can I get the page structure address of the remaining 7 pages?

They will be immediately following the first page structure in the
system memory map - they are contiguous pages, after all.  So just use
pointer arithmetic to find them.  

Inquiring minds are indeed curious as to why you need them, though :)
> 
> 2) There is a function page_address() which takes the page structure
> as an argument and returns the virtual address of the page
>  that is pointed by that page structure. 

Note that page_address() may not give you a valid address if it's a
high-memory page which is not currently mapped.

> Is there any method which
> retrives the address of the page structure?

Use virt_to_page() for normal kernel virtual addresses,
vmalloc_to_page() for memory in the vmalloc range.

jon

Re: How to get the address of the page structure from the given virtual address?

[B.Vinai Kumar]

Hi Jon,

Thanks for your response.

I'am writing a kernel socket which calls the tcp_sendpage (modified to
take array of pages) to send the data out
of the kernel socket. I'am allocating 32K of data by calling
alloc_pages and want to send this 32K of data. I modified the
tcp_sendpages to take an array of page structures.

Original version takes pointer to single page structure as an argument.

I will use the above calls to get the address of the page structure
and let you know.

Thanks
Vinai.