[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] [PATCH] Prevent xl save from segfaulting when control/shutdown key is removed
On Wed, 2011-11-23 at 13:12 +0000, Paul Durrant wrote: > True. I was conflating the key rm issue with the fact that the > XenServer Windows PV guest agent gets unhappy because it can't > advertise its features (which I hadn't mentioned before). > > I suppose that libxl will just have to continue to speculatively write > control/shutdown and timeout if it's not NUL-ed or rm-ed as it does > now. I suppose one option might be a "feature-will-write-features" flag. If it is not written to true then assume everything is supported, if it does get set to true then look for the flags and follow them. However if a protocol is going to be invented then it should be discussed here and documented etc. Ian. > > Paul > > > -----Original Message----- > > From: Ian Campbell > > Sent: 23 November 2011 13:05 > > To: Paul Durrant > > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx > > Subject: RE: [Xen-devel] [PATCH] Prevent xl save from segfaulting > > when control/shutdown key is removed > > > > On Wed, 2011-11-23 at 12:59 +0000, Paul Durrant wrote: > > > > -----Original Message----- > > > > From: Ian Campbell > > > > Sent: 23 November 2011 11:24 > > > > To: Paul Durrant > > > > Cc: xen-devel@xxxxxxxxxxxxxxxxxxx > > > > Subject: RE: [Xen-devel] [PATCH] Prevent xl save from > > segfaulting > > > > when control/shutdown key is removed > > > > > > > > On Wed, 2011-11-23 at 11:19 +0000, Paul Durrant wrote: > > > > > what is the reason for creating control ro to the guest? > > > > > > > > In general libxl prefers to whitelist paths which the guest can > > > > write too, just to prevent a complete free for all, keep things > > > > somewhat under control and to help avoid situations where tools > > > > might inadvertently rely on a guest-writeable key in an unsafe > > way.. > > > > > > > > > In XenServer we allow the guest to write the control key to > > > > advertise > > > > > feature-shutdown, feature-suspend etc. so that the tools know > > what > > > > > values of control/shutdown the guest will respond to. > > > > > > > > The libxl way would be to create these at build time (perhaps > > empty) > > > > with the appropriate permissions. > > > > > > > > It's not clear how that functionality can be added in a way > > which is > > > > compatible with existing guests though, e.g. no Linux guest > > writes > > > > those but many can be suspended etc. > > > > > > > > > > So the simple solution, for compatibility's sake, is to make > > control rw isn't it? > > > > The problem I'm thinking of exists even if control is rw. > > > > Given an empty control directory how do you know if a guest supports > > suspend or not, given that most existing guests which do support > > suspend do not write any key there? > > > > Ian. > _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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