On Mon, Dec 14, 2020 at 11:35:12PM -0700, Chris Murphy wrote:
> Squashfs doesn't have error detection for its metadata or the data
> contained in it. I'm not sure why you're having such a high success
> rate. Whether lossy or lossless compression algorithms in images, my
> experience it is only sometimes results in an error, often we just get
> artifacts. i.e. a bit flip turns into multiple wrong bytes of image
> data, sometimes an entire row of pixels gets obliterated (thousands).
> It just depends on what gets hit. But maybe lzma, which is what xz is
> based on and what's used in squashfs images currently, could be
> particularly susceptible to bit flips translating into something
> detectable.

It seems so. I mean, I can do more than a thousand tests if it helps, but
that was enough to convince _me_. 



> But also, we're not using unsquashfs for boot or installation. The
> squashfs image is loop mounted and treated as a random access file
> system. Decompression of blocks is on demand.

So I guess the next thing is: what's the error handling when the kernel hits
an uncompress error when reading a compressed squashfs on the fly? It'd be
kind of exciting if it logs an error we could actually watch for and pop up
a message saying "so, yeah, your USB stick is bad...."

-- 
Matthew Miller
<mat...@fedoraproject.org>
Fedora Project Leader
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