From mboxrd@z Thu Jan 1 00:00:00 1970 From: Andrew Cooper Subject: Re: [PATCH] tools/migrate: Fix regression when migrating from older version of Xen Date: Thu, 11 Jul 2013 12:09:33 +0100 Message-ID: <51DE926D.2050004@citrix.com> References: <1373483987-32343-1-git-send-email-andrew.cooper3@citrix.com> 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.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: George Dunlap Cc: Ian Jackson , Ian Campbell , Xen-devel List-Id: xen-devel@lists.xenproject.org On 11/07/13 10:46, George Dunlap wrote: > On Wed, Jul 10, 2013 at 8:19 PM, Andrew Cooper > wrote: >> Commit 00a4b65f8534c9e6521eab2e6ce796ae36037774 Sep 7 2010 >> "libxc: provide notification of final checkpoint to restore end" >> broke migration from any version of Xen using tools from prior to that commit >> >> Older tools have no idea about an XC_SAVE_ID_LAST_CHECKPOINT, causing newer >> tools xc_domain_restore() to start reading the qemu save record, as >> ctx->last_checkpoint is 0. >> >> The failure looks like: >> xc: error: Max batch size exceeded (1970103633). Giving up. >> where 1970103633 = 0x756d6551 = *(uint32_t*)"Qemu" >> >> Sadly, the simple fix of just setting ctx->last_checkpoint = 1 will cause an >> opposite function regresson for anyone using the current behaviour of >> save_callbacks->checkpoint(). >> >> The only safe fix is to rely on the toolstack to provide this information. >> >> Passing 0 results in unchanged behaviour, while passing nonzero means "the >> other end of the migration stream does not know about >> XC_SAVE_ID_LAST_CHECKPOINT but is performing a normal migrate" >> >> Signed-off-by: Andrew Cooper > Shouldn't there also be a way to actually use the flag? > > -George How do you mean? Plumb it up through to xl? xl (in any non-experemental form) post-dates this regression. xend predates it, but I can't find any way of working out whether the far end predates the regression. ~Andrew