[Virtio-fs] Current file handle status and open questions

[Stefan Hajnoczi]

On Wed, Mar 24, 2021 at 01:28:48PM +0100, Max Reitz wrote:
> On 24.03.21 12:51, Stefan Hajnoczi wrote:
> > On Thu, Mar 18, 2021 at 06:09:58PM +0100, Max Reitz wrote:
> > > So, overall it seems like it may be workable to extend the in-kernel MAC
> > > verification to allow for persistent keys, but I still have some open
> > > questions, and I don’t know whether I should just defer them until we
> > > get to the point where we need persistency.
> > 
> > It seems worth refining these ideas a little bit further until they
> > reach solid ground. Then we can be sure that there is at least one
> > possible solution. At the moment it seems like most the components of a
> > solution are known but it's not clear how they all fit together - and
> > they have a nasty tendency of failing to meet the requirements if they
> > aren't put together in exactly the right way :).
> > 
> > > (Of note: If we implement something where a user space process (or
> > > multiple in conjunction) can arbitrarily choose a MAC key, then this
> > > will also be usable for live migration, because you can continue to use
> > > the key from the source on the destination.)
> > 
> > Definitely. Taking migration into account is worthwhile. One question
> > about that:
> > 
> > Are Linux file handles transferrable between systems? Basic
> > configurations that come to mind:
> > 1. XFS, brtfs, ext4 on SAN (e.g. FibreChannel SCSI LUN)
> > 2. NFS
> > 
> > I assumed they were in previous discussions but has anyone checked the
> > file handle implementations to see whether this is really the case?
> 
> I’m not exactly sure what you mean.  I think you’re asking whether for a
> single (shared) filesystem a file handle always works independently of which
> Linux instance is using it?

Yes. What you've found sounds promising.

Stefan
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