Re: VM_XIP Request for comments

[Jared Hulbert <jaredeh@gmail.com>]

On 10/27/05, Christoph Hellwig <hch@infradead.org> wrote:
> On Tue, Oct 25, 2005 at 03:42:25PM -0700, Jared Hulbert wrote:
> > What would it take to get this first patch in the kernel?
> >
> > The reason for the first patch is in the second patch, which I will
> > try to get into the kernel list.  With this mmap()'ed files can be
> > used directly from flash when possible and COW's it when necessary..
>
> Can't you use the XIP infrastructure we already have?  Grep for
> CONFIG_XIP and CONFIG_EXT2_FS_XIP

I can't find CONFIG_XIP.  But I assume you are talking about
filemap_xip.c and Documentation/filesystems/xip.txt.

Hmm.

I don't know. The code and discussions about it looked very big-iron
DSCC specific but now on second pass it was meant to more generic.  If
I can learn this infrastructure then maybe this will work.

So I'm supposed to create a function in the target fs that gets
plugged into get_xip_page().  Then I call that function to create an
proper XIP'ed page in my mmap() and fread() calls.  I could use the
first arg of get_xip_page() to pass in the start address of the cramfs
volume and the second the offset of the page in the file I want to
map.

Is that about right?

This is a lot more overhead than the current XIP Linear CRAMFS patches
but it would allow me choose a page-by-page compression/XIP scheme
rather than the file-by-file compression/XIP currently used in cramfs.
 Hmm.

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