On Sun, 2014-12-21 at 21:53 +0100, intrigeri wrote: > Hi, > > intrigeri wrote (11 Dec 2014 13:13:43 GMT) : > > Ben Hutchings wrote (09 Dec 2014 19:55:10 GMT) : > >> Please try the Linux 3.18 packages from experimental (they're not there > >> yet, but should be soon) and check that overlayfs does what you need. > > > Thanks. I'll test it for Tails' usecases (that use aufs a bit more > > than most other live systems, e.g. our incremental upgrades features > > uses it) once I find the time to. > > Here are the results of our preliminary investigations: > > 1. Due to overlayfs' stack depth limit of 2, until support more than > one read-only lower layer is completed, overlayfs breaks > live-boot's SquashFS stacking feature; Tails "automatic upgrades" > rely on this feature. The current overlayfs maintainer says it is > the "top feature request", and has been working on it recently > (https://www.mail-archive.com/linux-unionfs@vger.kernel.org/msg00079.html). > The code lives in > git://git.kernel.org/pub/scm/linux/kernel/git/mszeredi/vfs.git > (branch overlayfs-next, currently). Should we expect this to be merged in Linux 3.20? > Later on the same thread, there are also patches > (https://www.mail-archive.com/linux-unionfs@vger.kernel.org/msg00088.html) > to make the stack depth limit configurable at runtime, but it was > deemed risky by the overlayfs maintainer without more work to check > that the stack will be safe. So, our best bet right now seems to > wait for the >1 read-only lower layer feature. > > 2. Whiteouts support *should* work when using SquashFS (for > non-directories, using a char device; for directories, using > a xattr to make them opaque). Not tested yet, though. We also rely > on this feature for Tails "automatic upgrades". > > Is it an option to get aufs back into the Debian kernel until #1 is > completed and reaches mainline? (I could understand that you want to > add a deadline if you make such a promise, of course :) I would rather apply the overlayfs patches to support multiple lower layers. Ben. -- Ben Hutchings Reality is just a crutch for people who can't handle science fiction.
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