Messages in this thread | | | Date | Mon, 21 Nov 2005 07:50:50 -0800 | From | Matt Mackall <> | Subject | Re: [PATCH] skip initramfs check |
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On Mon, Nov 21, 2005 at 09:04:46AM -0600, Rob Landley wrote: > 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_init(whatever) > deflate_next_x_bytes(source *, dest *, length) > > To grab a the first X bytes from the initramfs image?
Not at the moment. But I think it is feasible to simply move the ramdisk detection and unpacking inside the ramfs state machine. In other words, add two new states:
- detecting type - unpacking ramdisk
When the first few bytes are fed from the decompressor to the state machine, we either transition to the normal ramfs unpacking or we treat it as a ramdisk.
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