Date: Fri, 4 Mar 2016 16:54:10 +0100 From: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= <roger.pau@citrix.com> To: =?UTF-8?Q?Gustau_P=C3=A9rez?= <gustau.perez@gmail.com> Cc: =?UTF-8?Q?Roger_Pau_Monn=C3=A9?= <roger.pau@citrix.com>, FreeBSD XEN <freebsd-xen@freebsd.org> Subject: Re: Porting the block-iscsi hotplug script Message-ID: <alpine.OSX.2.20.1603041647160.22025@mac> In-Reply-To: <56D97762.7000908@gmail.com> References: <553DEB97.5000300@entel.upc.edu> <555EF542.3090002@citrix.com> <555F9B3F.1000600@entel.upc.edu> <55602512.1090702@citrix.com> <56C6FA2F.8040900@gmail.com> <56CAC8CB.8030107@gmail.com> <56CADEDA.4050007@citrix.com> <56CB0057.1060509@gmail.com> <56CB041E.1020009@citrix.com> <56CB2D90.5080809@gmail.com> <56CB34BA.6060809@citrix.com> <56CC24BD.6050609@gmail.com> <56CC32E5.5010101@citrix.com> <56CC7637.3080408@gmail.com> <56CF5668.6090605@citrix.com> <56D0091F.80408@gmail.com> <56D02863.7040100@citrix.com> <56D03D95.9090509@gmail.com> <56D04E5F.8070901@citrix.com> <56D42A28.8050701@gmail.com> <56D434FC.8030905@citrix.com> <56D57110.2060406@gmail.com> <56D587D8.6030702@citrix.com> <56D590EA.609@gmail.com> <56D591BA.4020303@gmail.com> <56D5929F.7040001@citrix.com> <56D5C722.3080205@gmail.com> <56D6B68D.8080809@citrix.com> <56D7FEFE.9050000@gmail.com> <alpine.OSX.2.20.1603041055250.20397@mac> <56D97762.7000908@gmail.com>
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On Fri, 4 Mar 2016, Gustau Pérez wrote: > El 4/03/16 a les 11:00, Roger Pau Monné ha escrit: > > > > What other parameters do you want to pass to your script that cannot be > > fetched from xenstore? IMHO I was planning to only pass the xenstore > > backend node and the action. > > The action (if I understand it correctly) is already there. Yes, the xenstore backend path is $1 and the action $2. > > OTOH, I'd like to check if the disks are already in use, and so I'd > need to walk the /local/domain/0/backend/vbd/$domin/$devid/ looking if > the disks are already there. This arises two questions: > > * can I assume the domain0 store would always be /local/domain/0/? Hm, I wouldn't be on it. This is true in the most common scenario, where Dom0 (domain with id 0) runs all the backends. But if you are using a driver domain or a radically disagregated system (where control domain != hardware domain) this is no longer true. So in general you shouldn't make this assumption. > * would I need to walk for each $domid checking for each $devid and > getting the physical device? Linux already has some code to do this checking, but this also involves taking a lock in order to make sure there's only one hotplug script performing this check at the same time. The Linux function that performs this checking is in: http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/hotplug/Linux/block;h=2691b56951c9b82094471a141b9e0bed04abb929;hb=HEAD#l40 And the caller is: http://xenbits.xen.org/gitweb/?p=xen.git;a=blob;f=tools/hotplug/Linux/block;h=2691b56951c9b82094471a141b9e0bed04abb929;hb=HEAD#l275 If you take a look, the call to check_device_sharing is protected with the "block" lock. Roger.
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