Hello Iain, Iain Lane [2015-05-20 15:19 +0100]: > We sometimes come across bugs where software expects to be able to > rename files to work properly (either to atomically update, or perhaps > to disable some functionality). This doesn't work with our read-only > partition layout. We know how to work around this limitation by making > code changes, for example > > > https://code.launchpad.net/~seb128/whoopsie-preferences/touch-writable-image/+merge/259531
Indeed, I have similar hacks in systemd. Our current approach to making writable parts of /etc via file bind mounts is hopelessly doomed, as it breaks file system semantics like the one you mentioned. > to make use of a symlink into a writable directory. It's not a great > solution, not least because we have to implement it on a case-by-case > basis and we don't have any good way of proactively spotting the bugs - > they typically manifest themselves by settings not being saved but > people usually do not check for rename failures or surface these to the > user. > > Can anyone think of a way to fix this class of problem and remove the > need for us to have to go and patch code? Or at least to detect these > rename failures (check for EROFS) and aggregate them somewhere so that > they can be fixed. This is on touch - I'm not sure if snappy does > anything different here. TBH, the only clean way that I see is to flip the whole thing around. Keep /etc (and /var) writable, and instead deal with the things that should *not* be modified. I. e. ship them in e. g. /usr/etc/ and symlink/bind-mount them to /etc, or longer-term, get rid of them completely. IMHO this would be a much saner architecture than trying to play eternal catch-up with bugs like this and getting an ever-growing spaghetti heap of file bind mounts which we'll never be able to revert/change. Martin -- Martin Pitt | http://www.piware.de Ubuntu Developer (www.ubuntu.com) | Debian Developer (www.debian.org)
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