On 20 Apr 2016, at 17:18, Wouter Verhelst <w...@uter.be> wrote: > Hi Eric, > > On Wed, Apr 20, 2016 at 09:42:02AM -0600, Eric Blake wrote: > [...] >> But in 3.9, the overlap bug was still present, and the set of global >> flags had grown to include NBD_FLAG_NO_ZEROS (commit 038e066), which >> overlaps with NBD_FLAG_READ_ONLY. Ouch. This means that a client >> talking to a server that advertises NO_ZEROES means that the client will >> mistakenly tell the kernel to treat EVERY export as read-only, even if >> the client doesn't respond with NBD_FLAG_C_NO_ZEROES. >> >> 3.10 fixed things; negotiate() now uses uint16_t *flags (instead of u32 >> *), and no longer tries to merge global flags with transmission flags; >> only the transmission flags are ever passed to the kernel via >> NBD_SET_FLAGS. Maybe it's good that there was only 2 weeks between 3.9 >> and 3.10, so hopefully few distros are trying to ship that broken version. > > Well, yeah, since 3.10 was an "oops" release when 3.9 exposed that bug > (which indeed had existed for a while) and which was reported quite > quickly on the list. Released versions of nbd which have the bug exist > though, and trying to have a 3.8 (or below) client talk to a 3.9 (or > above) server has the same issue. > > I decided that there was no way in which I could fix it, and that "the > export is readonly" is bad but not a "critical data loss" kind of bug, > so releasing 3.10 was pretty much the only sane thing I could do (other > than delaying NO_ZEROES, which might have worked too).
For what it's worth, Ubuntu 14.04 (still under long term support) ships with nbd-client 3.7 and I've just had a bug report filed against gonbdserver where all exports go readonly. https://github.com/abligh/gonbdserver/issues/4 I've added an option to disable NBD_FLAG_NO_ZEROS on nbd-server but that's pretty horrible. And I think this will affect all pre-3.10 clients talking to 3.9 and later servers. I'm going to find a minimal patch to nbd-client and offer that to Ubuntu / Debian. This message is here in part so I have something to point them at on the mailing list :-) -- Alex Bligh ------------------------------------------------------------------------------ Find and fix application performance issues faster with Applications Manager Applications Manager provides deep performance insights into multiple tiers of your business applications. It resolves application problems quickly and reduces your MTTR. Get your free trial! https://ad.doubleclick.net/ddm/clk/302982198;130105516;z _______________________________________________ Nbd-general mailing list Nbd-general@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/nbd-general
