Re: [Qemu-devel] [PATCH 2/5] Add SCM_RIGHTS support to unix socket character devices

[Avi Kivity]

On 07/08/2009 09:11 PM, Anthony Liguori wrote:
> Mark McLoughlin wrote:
> > It only makes sense to have one per getfd command and ...
>
> It would be silly to pass many fds.  fds are scarce resources and you 
> don't want to get into a position where you're queuing fds. 

If you issue N getfd commands, you've queued N fds.

> If a management tool wants to send an fd, it should issue the monitor 
> command that needs the fd along with the fd via SCM_RIGHTS, and then 
> wait for that command to complete before issuing another command that 
> needs an fd.

Why impose unnecessary restrictions?  I agree that the guest shouldn't 
use qemu as an fd store.  But putting such limits in the code is laying 
a trap for the client, which will show up in rare cases, for example two 
client threads issuing unrelated getfd commands with the client author 
not knowing it should serialize them.

--
I have a truly marvellous patch that fixes the bug which this
signature is too narrow to contain.