[stgt] [PATCH 1/1] Readonly disk LUNs

[FUJITA Tomonori]

On Sun, 4 Apr 2010 18:06:39 +1000
ronnie sahlberg <ronniesahlberg at gmail.com> wrote:

> On Sun, Apr 4, 2010 at 5:39 PM, FUJITA Tomonori
> <fujita.tomonori at lab.ntt.co.jp> wrote:
> > On Sun, 4 Apr 2010 08:50:54 +1000
> > ronnie sahlberg <ronniesahlberg at gmail.com> wrote:
> >
> >> There was a few minor details that would require re-working in my patch.
> >> For example "leaking" devicespecific code out into the spc
> >> mode-sense6/10 commands
> >> that would have to be done slightly differently.
> >
> > Just make sure that we all are on the same page. His requirement is
> > more complicated than your patch; read-only attribute "on
> > per-initiator basis". Probably, we need to extend the current security
> > model, all-or-nothing on per-initiator basis if we really want this.
> >
> 
> True.
> 
> For many dedicated HW platforms, you have one single taget that
> represents the entire device  and then using per LUN ACL rules to do
> remapping of LUN numbers on a per initiator basis or similar.
> That is when you often have per initiator ro mappings and even per
> initiator lun number remappings.
> 
> 
> 
> Software based targets like TGTD often have the possibility to create
> unlimited number of targets and thus can solve the same issue by
> target-level ACLs instead of per lun/initiator ACLs.
> 
> 
> 
> Craig,
> While not exactly as you are used to in what I assume are HW based
> iscsi boxens, instead of having readwrite/readonly settings based on
> the initiator level, would this be acceptable to your problem space ?
> 
> 
> You create TWO targets,   iqn.2010-04:readwrite and iqn.2010-04:readonly.
> On both these two targerts you create a LUN that uses the same backing
> store. I.e. two targets bot both use the same physical LUN.
> On the readonly target you flag this LUN as reaonly.
> 
> 
> Now you then use targetlevel ACLs and allow only readwrite initiators
> to access the readwrite target   but not the readonly target.
> You also use ALCs to make sure readonly initiators can only access the
> readonly target but not the readwrite target.
> 
> 
> 
> I.e.   difference in mechanism   but policy still available. On target
> lever instead of per lun acl level.
> 
> 
> 
> Something like this:
> 
> # create readwrite target and lumn
> tgtadm --lld iscsi --mode target --op new --tid 1 -T iqn.2010-03:readwrite
> tgtadm --lld iscsi --mode logicalunit --op new --tid 1 --lun 1 -b
> /backend-disk.img
> 
> # create a second target that is readonly but exports the same backing store
> tgtadm --lld iscsi --mode target --op new --tid 2 -T iqn.2010-03:readonly
> tgtadm --lld iscsi --mode logicalunit --op new --tid 2 --lun 1 -b
> /backend-disk.img
> tgtadm --lld iscsi --mode logicalunit --op update --tid 2 --lun 1
> --params readonly=1

This doesn't work for tgt since two targets doesn't share information
about the lu. For example, the mode page changed via the first target
can be seen via the second target.
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