Re: [PATCH] tcp_sendpage(): fix broken page iteration

From: Dan Aloni
Date: Sun Mar 18 2007 - 18:40:37 EST


On Sun, Mar 18, 2007 at 02:49:27PM -0700, David Miller wrote:
> From: Dan Aloni <da-x@xxxxxxxxxxxxx>
> Date: Sun, 18 Mar 2007 14:43:46 +0200
>
> > do_tcp_sendpages() should not iterate 'pages' as an array since
> > it is not an array of 'struct page *', but a pointer to a single
> > entity of 'struct page *' passed on the stack as a parameter to
> > tcp_send_page() (hence it would crash if poffset + psize > PAGE_SIZE,
> > because pages[1] and beyond most probably not constitutes a valid
> > 'struct page *').
>
> do_tcp_sendpages() should never get passed poffset+psize>PAGE_SIZE,
> that would be a bug.

Oh, then the name of that function was quite misleading...

Anyway, I thought it would make a valid case for a situation where
you have a kmalloc'ed buffer that happens to cross a page boundery
and you want to call ->sendpage() to send it over using network
DMA.

As I see it, with this constraint you either call sendpage twice or
you use kernel_sendmsg(), I am not sure which would me more
efficient - I guess it depends on psize. I wish there was a better
interface than sendpage that would have factored it in...

Thanks anyway for the heads up.

--
Dan Aloni
XIV LTD, http://www.xivstorage.com
da-x (at) monatomic.org, dan (at) xiv.co.il
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