[RFC PATCH] smbd: resilient file handle support

[Michael Adam]

On 2016-02-12 at 15:10 +0200, Uri Simchoni wrote:
> 
> 
> On 02/12/2016 12:38 AM, Michael Adam wrote:
> >On 2016-02-11 at 23:42 +0200, Uri Simchoni wrote:
> >>Hi,
> >>
> >>Attached pls find a patch for supporting resilient file
> >>handles. Comments are welcome. It doesn't include tests yet,
> >>but I would appreciate technical feedback and any other
> >>feedback.
> >Cool!
> >
> >A few comments up front before digging deeper into the
> >actual patches.
> >
> >Note the hacked up implementation (by metze) in the
> >master-multi-channel-obnox branch:
> >
> >https://git.samba.org/?p=obnox/samba/samba-obnox.git;a=commitdiff;h=8e68d390dc640ceb3aa9594c9d18d5d3d01c24f2
> >
> >samba.org/?p=obnox/samba/samba-obnox.git;a=shortlog;h=refs/heads/master-multi-channel-obnox
> OK that looks like a "fake resilient" implementation.
> 
> ><snip>
> >
> >One main difference is that while durable handles are purely
> >best effort, i.e. when a second client tries to open a file
> >with a disconnected durable handle, that handle is closed
> >and the original opener can not reconnect it. For resilient
> >handles, there are iirc (need to look up the exact details),
> >certain weak guarantees where new openers are blocked for
> >a short disconnected time. The same is true for persistent
> >handles, but with stronger guarantees and you can also get
> >them without oplocks, on a scale-out share.
> >
> >I think implementing these guarantees is the major challenge
> >in implementing resilient and durable handles.
> >
> ><snip>
> 
> >Cheers - Michael
> >
> >
> Thanks so much for summarizing what resilient handles are in technical terms
> - I could not find such a concise description anywhere so I tried to dig it
> from [MS-SMB2].
> 
> It looks like I got the differences-from-durable right (in my a-b-c list),
> but may be way off-base claiming that Samba's durable handles are already
> "resilient in disguise" (in that the original opener of a Samba durable
> handle can reconnect to it if someone else has opened the file while being
> disconnected).

Right, if there is a second attempt to open a file, while a durable
handle on this file is disconnected, the durable is closed /
destroyed and the new opener is afterwards the only opener of the
file. This like this in the doc (MS-SMB2) and in samba code.
(Will point out the corresponding code sections later.)

As you described, it is different with resilient handles.

Michael
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