From: Paul Durrant <Paul.Durrant@citrix.com> To: Bob Liu <firstname.lastname@example.org>, Ian Jackson <Ian.Jackson@citrix.com> Cc: "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, Roger Pau Monne <email@example.com>, "firstname.lastname@example.org" <email@example.com> Subject: Re: [RFC PATCH] blkif.h: document scsi/0x12/0x83 node Date: Wed, 16 Mar 2016 14:07:09 +0000 [thread overview] Message-ID: <60c0fa3b898c4ba5915dbf12d0413644@AMSPEX02CL03.citrite.net> (raw) In-Reply-To: <56E966A6.firstname.lastname@example.org> > -----Original Message----- > From: Bob Liu [mailto:email@example.com] > Sent: 16 March 2016 13:59 > To: Ian Jackson > Cc: firstname.lastname@example.org; Paul Durrant; email@example.com; > firstname.lastname@example.org; Roger Pau Monne; email@example.com > Subject: Re: [RFC PATCH] blkif.h: document scsi/0x12/0x83 node > > > On 03/16/2016 08:36 PM, Ian Jackson wrote: > > Bob Liu writes ("[RFC PATCH] blkif.h: document scsi/0x12/0x83 node"): > >> Sometimes, we need to query VPD page=0x83 data from underlying > >> storage so that vendor supplied software can run inside the VM and > >> believe it's talking to the vendor's own storage. But different > >> vendors may have different special features, so it's not suitable to > >> export through "feature-xxxx". > >> > >> One solution is query the whole VPD page through Xenstore node, which > has > >> already been used by windows pv driver. > >> > http://xenbits.xen.org/gitweb/?p=pvdrivers/win/xenvbd.git;a=blob;f=src/x > envbd/pdoinquiry.c > > > > Thanks for your contribution. > > > > Thanks also to Konrad for decoding the numbers, which really helps me > > understand what is going on here and helped me find the relevant > > references. > > > > (For background: I have just double-checked the SCSI spec and: INQUIRY > > lets you query either the standard page, or one of a number of `vital > > product data' pages, each identified by an 8-bit page number. The VPD > > pages are mostly full of vendor-specific data in vendor-specific > > format.) > > > > I have some qualms about the approach you have adopted. It is > > difficult to see how this feature could be used safely without > > knowledge specific to the storage vendor. > > > > But I think it is probably OK to define a specification along these > > lines provided that it is very clear that if you aren't the storage > > vendor and you use this and something breaks, you get to keep all the > > pieces. > > > >> + * scsi/0x12/0x83 > >> + * Values: string > >> + * A base64 formatted string providing VPD pages read out from > backend > >> + * device. > > > > I think this probably isn't the prettiest name for this node or > > necessarily the best format but given that this protocol is already > > deployed, and this syntax will do, I don't want to quibble. > > > > I would like the base64 encoding to specified much more explicitly. > > Just `base64 formatted' is too vague. > > > > > >> + * The backend driver or the toolstack should write this node with VPD > >> + * informations when attaching devices. > > > > I think this is the wrong semantics. I certainly don't want to > > encourage backends to use this feature. > > > > Rather, I would prefer something like this: > > > > * scsi/0x12/0x<NN> > > > > This optional node contains SCSI INQUIRY VPD information. > > <NN> is the hexadecimal representation of the VPD page code. > > > > A frontend which represents a Xen VBD to its containing operating > > system as a (virtual) SCSI target may return the specified data in > > response to INQUIRY commands from its containing OS. > > > > A frontend which supports this feature must return the backend- > > specified data for every INQUIRY command with the EVPD bit set. > > For EVPD=1 INQUIRY commands where the corresponding xenstore node > > does not exist, the frontend must report (to its containing OS) an > > appropriate failure condition. > > > > A frontend which does not support this feature (ie, which does not > > use these xenstore nodes), and which presents as a SCSI target to > > its containing OS, should support and provide whatever VPD > > information it considers appropriate, and should disregard these > > xenstore nodes. > > > > A frontend need not - and often will not - present to its > > containing OS as a device addressable with SCSI CDBs. Such a > > frontend has no use for SCSI INQUIRY VPD information. > > > > A backend should set this information with caution. Pages > > containing device-vendor-specific information should not be > > specified without the appropriate device-vendor-specific knowledge. > > > > That's much more clear, thank you very much! > > > > > Also I have two other observations: > > > > Firstly, AFAICT you have not provided any way to set the standard > > INQUIRY response. Is it not necessary in your application to provide > > If backends are not encouraged to use this node, then we must have the > toolstack write this node with the right VPD information. > Paul mentioned there should be corresponding code in the xapi project, but I > haven't found out where. > > > > synthetic vendorid and productid, at the very least ? > > > > Secondly, I think your hope that > > > >> blkfront in Linux ... can use the same mechanism. > > > > is I think misguided. blkfront does not present the disk (to the rest > > of the Linux storage system) as a SCSI device. Rather, Linux allows > > blkfront to present as a block device, directly, and this is what > > blkfront does. > > > > But we'd like to get the VPD information(of underlying storage device) also in > Linux blkfront, even blkfront is not a SCSI device. > > That's because our underlying storage device has some vendor-specific > features which can be recognized through informations in VPD pages. > And Our applications in guest want to aware of these vendor-specific > features. I think the missing piece of the puzzle is how the applications get this information. In Windows, since everything is a SCSI LUN (or has to emulate one) applications just send down 'scsi pass-through' IOCTLs and get the raw INQUIRY data back. In Linux there would need to be some alternative scheme that presumably blkfront would have to support. Paul > > Regards, > Bob > _______________________________________________ Xen-devel mailing list Xenfirstname.lastname@example.org http://lists.xen.org/xen-devel
next prev parent reply other threads:[~2016-03-16 14:07 UTC|newest] Thread overview: 27+ messages / expand[flat|nested] mbox.gz Atom feed top 2016-03-16 3:09 Bob Liu 2016-03-16 7:16 ` Konrad Rzeszutek Wilk 2016-03-16 12:36 ` Ian Jackson 2016-03-16 13:59 ` Bob Liu 2016-03-16 14:07 ` Paul Durrant [this message] 2016-03-17 5:04 ` Bob Liu 2016-03-16 14:32 ` David Vrabel 2016-03-17 5:07 ` Bob Liu 2016-03-17 11:12 ` Ian Jackson 2016-03-17 11:18 ` David Vrabel 2016-03-17 11:20 ` Ian Jackson 2016-03-22 12:55 ` Bob Liu 2016-03-22 13:41 ` David Vrabel 2016-03-22 14:10 ` Konrad Rzeszutek Wilk 2016-03-22 14:38 ` David Vrabel 2016-03-22 14:43 ` Paul Durrant 2016-03-22 15:09 ` Ian Jackson 2016-03-22 15:25 ` Paul Durrant 2016-03-22 16:14 ` Ian Jackson 2016-03-22 16:50 ` Konrad Rzeszutek Wilk 2016-03-22 17:39 ` Paul Durrant 2016-03-22 15:12 ` Ian Jackson 2016-03-22 15:27 ` Konrad Rzeszutek Wilk 2016-03-22 16:11 ` Ian Jackson 2016-03-22 16:38 ` Konrad Rzeszutek Wilk 2016-03-22 16:25 ` Jan Beulich 2016-03-16 14:33 ` Ian Jackson
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