Re: [PATCH] skip initramfs check

From: Rob Landley
Date: Mon Nov 21 2005 - 10:05:22 EST

On Monday 21 November 2005 00:23, Marcelo Tosatti wrote:
> Hi Rob,
> > Query: is the problem that a big initramfs image is being unpacked more
> > than once, or is unpacking an empty initramfs image (134 bytes) causing a
> > significant delay?
> The problem is a big non-initramfs RAMDISK image (used for root mountpoint
> on this particular embedded platform), that is decompressed more than once:
> - during the initramfs check, which fails because it is not initramfs.
> - during the real RAMDISK decompression to memory.
> > I'm fairly certain that back in 1990 I could unzip 134 bytes on my 33 mhz
> > 386 running dos in a fraction of a second. What's the use case here?
> So the issue is not the empty initramfs image (which BTW could probably
> be made unecessary?), but a 10Mb RAMDISK image being decompressed by a
> 48Mhz PPC, which takes quite a few seconds.
> Need to rework the patch to use a __setup option as Andrew suggested.

It sounds to me like is the initial check (which is just giving a thumbs
up/thumbs down "is this an initramfs", correct?) only needs to decompress the
first page or so of data to make this determination. A quick glance at the
code seems to imply it's just checking the header and the first entry, so 4k
should be plenty for that.

Some variant of lib/zlib_inflate... Ouch, bit of a mess there. Hey Matt: you
know this area. Is it feasible to do some kind of:

deflate_next_x_bytes(source *, dest *, length)

To grab a the first X bytes from the initramfs image?

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