On 21/10/14 08:19, Martin Lucina wrote:
> [better control for block device limitations]
>
> There are three approaches to how this could be done in the rump_etfs API:
>
> 1) Change the ftype argument to a bitmask and include RUMP_O_XXXX as
> possible flags. This is the minimal API change, but not very pretty.
>
> 2) Add a oflags argument to rump_pub_etfs_register.
>
> 3) Add a new API where instead of hostpath the caller passes in an existing
> file descriptor. This seems like the most flexible approach.
>
> What do you think?

Humh, well, the problem is certainly valid.

Your "3" proposal seems like an adequate quick solution.  Though, it 
doesn't make a whole lot of sense for platforms without file descriptors 
(e.g. Xen blkfront).

therefore ...

I've been wanting to revamp the "virtual" block device interface and 
code a bit more.  For example, currently it's not possible to use more 
than one block device.  Example: assume you want to choose between an 
aio backend and read/write backend.  For network interfaces this already 
works: you can have for example a dpdk interface and a netmap interface 
in the same rump kernel and send some traffic out of one and other 
traffic out of a another.

So, if you want a hobby in addition to a solution, the above is 
something I'd like to fix (or see fixed).  Per minimum, it requires 
rethinking the rump_pub_etfs API.  I'm not sure the magical invisible 
devices created by rump_etfs are the best possible idea...

After all, I think the block device code in rump kernels got rewritten 
over the years only once, and I think etfs got no rewrites.  That's 
pretty exceptional in rump kernel context ;)

> This is something we could do on the hackathon in November, if I don't get
> to it before.

Yes, definitely, we're holding the hackathon exactly for things like this.

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