From mboxrd@z Thu Jan 1 00:00:00 1970 From: George Dunlap Subject: Re: [PATCH] libxl: stat the path for all non-qdisk backends (including unknown) Date: Fri, 10 May 2013 15:19:32 +0100 Message-ID: <518D01F4.1010103@eu.citrix.com> References: <1366985563-10926-1-git-send-email-ian.campbell@citrix.com> <1366986572.3142.116.camel@zakaz.uk.xensource.com> <518CFF7E.1080408@eu.citrix.com> Mime-Version: 1.0 Content-Type: text/plain; charset="us-ascii"; Format="flowed" Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <518CFF7E.1080408@eu.citrix.com> List-Unsubscribe: , List-Post: List-Help: List-Subscribe: , Sender: xen-devel-bounces@lists.xen.org Errors-To: xen-devel-bounces@lists.xen.org To: Dave Scott Cc: "xen-devel@lists.xen.org" , Sylvain Munaut , Ian Jackson , Ian Campbell , Roger Pau Monne List-Id: xen-devel@lists.xenproject.org On 10/05/13 15:09, Dave Scott wrote: > On 10/05/13 14:46, George Dunlap wrote: >> On Fri, Apr 26, 2013 at 3:29 PM, Ian Campbell wrote: >>> On Fri, 2013-04-26 at 15:17 +0100, Sylvain Munaut wrote: >>>>> Since the intention of that commit was to allow for qdisk backends with no >>>>> explicit file in dom0 (i.e. network remote backend such as ceph) the lowest >>>>> impact fix appears to be to make that explicit. This should probably be >>>>> revisited to rationalize the probing. >>>> What about the remote disk case of blktap ? blktap2.5 supports NBD >>>> already AFAIK >>>> and I'm pretty sure I'll hit that same stat issue soon for another >>>> remote blktap case. >>> Right, sounds like I should have gone with my first instinct which was: >>> >>> 8<------------------------------------------------------------ >>> >>> From 884beff4a897d785f61705dcfa2f048536982d7c Mon Sep 17 00:00:00 2001 >>> From: Ian Campbell >>> Date: Fri, 26 Apr 2013 12:41:43 +0100 >>> Subject: [PATCH] libxl: stat the path for all non-qdisk backends (including unknown) >>> >>> The commit a8a1f236a296 "libxl: Only call stat() when adding a disk if we >>> expect a device to exist." changed things to only stat the file when the phy >>> backend was explicitly requested. This broke the case where we are probing and >>> would normally be able to decide on the phy option. >> So at the moment qdisk backends aren't checked at all with this -- >> which means that if you give a path to a file that doesn't exist via, >> for example, xl cd-insert, things fail in weird ways: >> >> 1. In qemu-traditional, the command silently completes; the effect is >> that the disk currently in the drive is ejected >> >> 2. in qemu-upstream, qmp returns an error which is reported. The disk >> is ejected from the guest, but the xenstore entries are not updated >> (still contain the old values) >> >> It seems like we should probably also at least check if disk_format is RAW. >> >> OTOH, I don't seen an option for disk_format to be ceph; is it just >> listed as "raw" as well? That doesn't seem right... > AFAICT a ceph disk is in the "raw" format but it uses a custom network > protocol to actually read and write the blocks. I imagine on the ceph > servers the disk is stored in a cleverer format, but all qemu/tapdisk > see are plain blocks with no fancy encoding, no .vhd or .qcow. Oh, hang on -- does qdisk / tapdisk then just open a plain file? Then it *is* just a raw file for these purposes; and we should still be able to call stat() on it. I guess I'm not yet clear why qdisk files are excluded from the stat(). Under what circumstances would disk->pdev not be a valid file if disk->backend_domid == LIBXL_TOOLSTACK_ID? -George