On 04/27/2010 11:48 AM, Dor Laor wrote:
Here's another option: an nbd-like protocol that remotes all BlockDriver
operations except read and write over a unix domain socket. The open
operation returns an fd (SCM_RIGHTS strikes again) that is used for read
and write. This can be used to implement snapshots over LVM, for example.



Why w/o read/writes?

To avoid the copying.

the watermark code needs them too (as info, not the actual buffer).

Yeah.  It works for lvm snapshots, not for watermarks.


IMHO the whole thing is way over engineered:
 a) Having another channel into qemu is complicating management
    software. Isn't the monitor should be the channel? Otherwise we'll
    need to create another QMP (or nbd like Avi suggest) for these
    actions. It's extra work for mgmt and they will have hard time to
    understand events interleaving of the various channels

block layer plugins allow intercepting all interesting block layer events, not just write-past-a-watermark, and allow actions based on those events. It's a more general solution.

 b) How the plugins are defined? Is it scripts? Binaries? Do they open
    their own sockets?

Shared objects.


--
error compiling committee.c: too many arguments to function

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