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

Russell Senior russell at personaltelco.net
Fri Aug 30 17:10:54 EDT 2019

>>>>> "Christian" == Christian Lamparter <chunkeey at gmail.com> writes:

Christian> Ok.

Christian> I did push a patch titled: "build: remove harmful -nopad
Christian> option from mksquashfs"
Christian> <https://git.openwrt.org/?p=openwrt/openwrt.git;a=commit;h=1c0290c5cc6258c48b8ba46b4f9c85a21de4f875>

Christian> so, let's see if this triggers more undefined behaviour and
Christian> exposes more hidden broken code.

Just to re-iterate my earlier worry, if for example:

  kernel_size + rootfs_with_padding_size

crosses an erase block boundary that:

  kernel_size + rootfs_without_padding_size

does not, then we'll be wasting an erase block of flash space on NOR.

On a side note, I noticed that there were some checks[1] added to
kernels about a year ago (early august 2018) to squashfs code[1], to
protect against malformed squash filesystems that might have started
triggering the boot loop. This might explain why we haven't seen the
problem earlier (it might have been silently ignored).

[1] e.g. https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=71755ee5350b63fb1f283de8561cdb61b47f4d1d

Russell Senior, President
russell at personaltelco.net

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