Re: [Qemu-devel] [PATCH 4/4] block: avoid creating oversized writes in multiwrite_merge

[Paolo Bonzini]

Il 22/09/2014 11:43, Peter Lieven ha scritto:
> This series aims not at touching default behaviour. The default for 
> max_transfer_length
> is 0 (no limit). max_transfer_length is a limit that MUST be satisfied 
> otherwise the request
> will fail. And Patch 2 aims at catching this fail earlier in the stack.

Understood.  But the right fix is to avoid that backend limits transpire
into guest ABI, not to catch the limits earlier.  So the right fix would
be to implement request splitting.

Since we never had a bug report about this, I'm not pushing to implement
splitting.  However, patch 2 is still wrong.

Patch 4 instead is fixing a real bug, so it's very much welcome.

Paolo

> Currently, we only
> have a limit for iSCSI. Without Patch 2 it would fail after we have send
> the command to
> the target. And without Patch 4 it may happen that multiwrite_merge
> traps the into the limit.
> 
> Maybe I should adjust the description of max_transfer_length?