From mboxrd@z Thu Jan 1 00:00:00 1970 From: Keir Fraser Subject: Re: [PATCH 0 of 5] Make checkpointing backwards compatible with older kernels Date: Sat, 13 Jan 2007 09:28:55 +0000 Message-ID: References: Mime-Version: 1.0 Content-Type: text/plain; charset="US-ASCII" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xensource.com Errors-To: xen-devel-bounces@lists.xensource.com To: Brendan Cully , xen-devel@lists.xensource.com List-Id: xen-devel@lists.xenproject.org On 12/1/07 10:03 pm, "Brendan Cully" wrote: > This set of patches makes checkpointing backwards compatible with > older kernels. Checkpointable kernels now create a xenstore entry > called "control/feature-resumable" which xc save -c checks before > attempting to checkpoint a domain. > > It also writes a new SIF_RESUMABLE flag into the suspend record, > which xc_linux_restore uses to decide whether it is safe to set the > hypercall return value. A single unified new elfnote would probably be better. We would like a new libxc function to pull image metadata (inc. Elfnotes) out of a kernel image and provide a comma-separated key-value list, turned into a dictionary for Python consumption. This would then be persisted by xend (e.g., be added to save/restore stream format) and can be used to decide whether 'xm save -c' is okay, and would allow info to be passed to xc_save/xc_restore about whether suspend is resumable. We already have another intended use for this mechanism, which is to provide a pte mask to use to decide whether or not a not-present pte contains an MFN (needing conversion to PFN on xc_save). Unfortunately although this method is cleanest there is some tedious plumbing to be done and I'm not sure how to represent the Elf notes in a save image format (perhaps it can be merged into the image sxpr). Yes -- returning 1 on resume (rather than restore) will allow new guest kernels to run properly on old Xen and tools which do not understand resume, so that would be the better way round. -- Keir