linux-kernel - Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

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Date:	Fri, 13 Apr 2007 11:01:41 +1000
From:	Nick Piggin <nickpiggin@...oo.com.au>
To:	Matt Mackall <mpm@...enic.com>
CC:	Andrew Morton <akpm@...ux-foundation.org>,
	William Lee Irwin III <wli@...omorphy.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 0/13] maps: pagemap, kpagemap, and related cleanups

Matt Mackall wrote:
> On Fri, Apr 13, 2007 at 10:15:24AM +1000, Nick Piggin wrote:
> 
>>Andrew Morton wrote:
>>
>>>On Thu, 12 Apr 2007 16:10:50 -0700
>>>William Lee Irwin III <wli@...omorphy.com> wrote:
>>
>>>>+       while (count > 0) {
>>>>+               chunk = min_t(size_t, count, PAGE_SIZE);
>>>>+               i = 0;
>>>>+
>>>>+               if (pfn == -1) {
>>>>+                       page[0] = 0;
>>>>+                       page[1] = 0;
>>>>+                       ((char *)page)[0] = (ntohl(1) != 1);
>>>
>>>
>>>OK.
>>>
>>>
>>>
>>>>+                       ((char *)page)[1] = PAGE_SHIFT;
>>>
>>>
>>>OK.
>>
>>Shouldn't we just expose page size and endianness by other means? (another 
>>file or
>>syscall).
> 
> 
> If I send you this file dumped from a random machine, you won't know
> what to make of it.

That's a good reason ;)

> I'm planning to write a trivial server to sit on, say, my embedded
> target and spew this over the wire to a client. 
> 
> 
>>>Not a good idea to expose raw flags in this manner - it changes at the drop
>>>of a hat.  We'd need to also expose the kernel's PG_foo-to-bitnumber
>>>mapping to make this viable.
>>
>>I don't think it is viable because that makes the flags part of the
>>userspace ABI. I wonder what they are needed for.
> 
> 
> Basically: to show what the hell's going on in the VM.

kprobes / systemtap isn't good enough?

-- 
SUSE Labs, Novell Inc.
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