Re: [Qemu-devel] [PATCH 2/3] scsi: replace 'tag' with 'hba_private' pointer

[Paolo Bonzini]

On 07/01/2011 03:11 PM, Hannes Reinecke wrote:
> On 07/01/2011 10:27 AM, Paolo Bonzini wrote:
> > On 07/01/2011 09:42 AM, Hannes Reinecke wrote:
> > > 'tag' is just an abstraction to identify the command
> > > from the driver. So we should make that explicit by
> > > replacing 'tag' with a driver-defined pointer 'hba_private'.
> > > This saves the lookup for driver handling several commands
> > > in parallel.
> >
> > This makes tracing a bit harder to follow. Perhaps you can keep the
> > transport tag (a uint64_t) in the SCSIRequest for debugging purposes?
> Hmm. The transport tag wouldn't have any meaning outside scsi-bus.c.

It depends, in vmw_pvscsi I take it from a field in the request block 
that is 0..255.  So either you have a small tag that is recycled but 
stays nice, or a large tag that is unwieldy but should not be recycled 
ever.  A pointer is unwieldy _and_ is recycled, so it gives the worse of 
both worlds.

But I'm not very attached to this, I may even do it myself if/when I 
find the need.  Won't ack yet because of the nit with ESP/USB, but even 
if you do not bother I will ack the next respin.

Paolo