[OpenWrt-Devel] Squashfs breakage lottery with UBI WAS: [PATCH RFC 2/2] amp821xx: use newly added pad-squashfs for Meraki MR24

Christian Lamparter chunkeey at gmail.com
Sun Sep 1 14:46:11 EDT 2019


On Sun, Sep 1, 2019 at 1:52 PM Russell Senior <russell at personaltelco.net> wrote:
> >>>>> "Jonas" == Jonas Gorski <jonas.gorski at gmail.com> writes:
> >> It contains a patch at the end titled: "[PATCH] base-files: pad
> >> root.squashfs to 64KiB in ubi volumes" This is another approach that
> >> just deals with the UBI+squashfs issue but works with
> >> "-nopad". Soooooo.... do we all agree there?
> Jonas> a) 64k is excessive, we only need 4k (actually 1k would be
> Jonas> enough, since we don't enable CONFIG_SQUASHFS_4K_DEVBLK_SIZE).
> Jonas> The referenced issue with 64k page size happens when
> Jonas> loop-mounting a squashfs, since loop defaults to PAGE_SIZE as its
> Jonas> block size. But we never do that in OpenWrt, and we don't support
> Jonas> any targets with that huge PAGE_SIZE - biggest is ARC with 8k.
> Jonas> b) it misses the squashfs's in generic sysupgrade images itself -
> Jonas> we need to pad their length as well, to avoid breaking devices
> Jonas> with a sysupgrade image hitting the corner case being flashed
> Jonas> from an unfixed firmware with the old nand.sh.
> Jonas> Also IMHO "1c0290c5cc6258c48b8ba46b4f9c85a21de4f875" should be
> Jonas> reverted, for the previously mentioned issues.
> Afaict, only devices with LEB sizes of non-integer kilobytes (like the
> MR24 with its 15.5k LEBs) need any intervention at all. Because
> squashfs's are read in 1k blocks, there is a 1 in 62 chance of creating
> a rootfs that is an inopportune size on 15.5k LEBs.  I have a PogoPlug
> v3 with LEBs of 126k, and a MikroTik RouterBOARD 493G with LEBs of
> 124k. Neither of those is affected.
> I still kind of like my solution where we explicitly ask for padding for
> devices that need it.

I see, fine.

Tell you what, I'll let the two of you do what you want or not.
My request to the both of you is, that instead of justreverting, please add  a
"why the -nopad has become essentially atechnical debt there". I'm not that
familiar with these devices and their problems, so I don#t think I have anything
more to add.


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