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d="scan'208";a="16683154" Subject: Re: [PATCH] tools/xenstore: don't store domU's mfn of ring page in xensotred To: =?UTF-8?B?SsO8cmdlbiBHcm/Dnw==?= , Julien Grall , Julien Grall References: <20200428155144.8253-1-jgross@suse.com> <76ed29d6-e2fc-cd48-6de7-e0032daaa2e9@xen.org> <3fd79cb1-e18f-1987-69ff-94f1bd15c66f@citrix.com> <3dcbe001-c66c-13a6-7a28-ef24b05eefa0@suse.com> From: Igor Druzhinin Message-ID: Date: Wed, 29 Apr 2020 12:04:44 +0100 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0 MIME-Version: 1.0 In-Reply-To: <3dcbe001-c66c-13a6-7a28-ef24b05eefa0@suse.com> Content-Type: text/plain; charset="utf-8" Content-Language: en-US Content-Transfer-Encoding: 8bit X-BeenThere: xen-devel@lists.xenproject.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Xen developer discussion List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Cc: xen-devel , Ian Jackson , Wei Liu , "andrew.cooper3@citrix.com" Errors-To: xen-devel-bounces@lists.xenproject.org Sender: "Xen-devel" On 29/04/2020 11:49, Jürgen Groß wrote: > On 29.04.20 12:39, Igor Druzhinin wrote: >> On 29/04/2020 10:22, Julien Grall wrote: >>> Hi Juergen, >>> >>> On 29/04/2020 06:51, Jürgen Groß wrote: >>>> >>>> Recreating the event channel would be fine, but I don't see why it >>>> would ever be needed. And XS_INTRODUCE is called only at domain creation >>>> time today, so there is obviously no need for repeating this call. >>>> >>>> Maybe the idea was to do this after sending a XS_RESUME command, which >>>> isn't used anywhere in Xen and is another part of Xenstore which doesn't >>>> make any sense today. >>> >>> Commit f6cc37ea8ac71385b60507c034519f304da75f4c "tools/oxenstored: port XS_INTRODUCE evtchn rebind function from cxenstored" added the exact same behavior in the OCaml XenStored last year. >>> >>> This was introduced 12 years after C XenStored, so surely someone think this is useful. We should check why this was introduced in OCaml XenStored (I have CCed the author of the patch). >>> >>> If we still think this is not useful, then you should add an explanation in the commit message why the two implementations diverge and possibly update the spec. >> >> Thanks for CC, Julien. >> >> We indeed already use this functionality in our toolstack for guest kdump >> functions. It's not possible in XAPI to adopt libxl model where almost everything >> is restarted for a domain entering kdump, so we have to use this message to >> rebind xenstore evtchn after soft reset without shutting down backends and >> recreating the whole subtree (frontends reconnect fine after that). >> >> We obviously only require it for now to be present in oxenstored only. >> Please don't remove this functionality if possible. > > If I read handling in libxl correctly, in the soft reset case XS_RELEASE > is issued before doing another XS_INTRODUCE. XS_RELEASE will result in > xenstored throwing away its related struct domain, so XS_INTRODUCE will > be possible again. >From what I remember it was not possible to keep xenstored data for a domain and at the same time perform release-introduce cycle (at least in oxenstored). It also involved firing @releaseDomain which caused havoc in other part of the toolstack. Igor