On 07/05/2015 16:34, Kevin Wolf wrote: > Am 07.05.2015 um 16:16 hat Paolo Bonzini geschrieben: >> >> >> On 07/05/2015 16:07, Kevin Wolf wrote: >>> This is not right for two reasons: The first is that this is >>> BlockBackend code >> >> I think it would take effect for the qemu-nbd case though. > > Oh, you want to change the server code rather than the client?
Yes. > Wait... Are you saying that NBD sends a (platform specific) errno value > over the network? :-/ Yes. :/ That said, at least the error codes that Linux places in /usr/include/asm/errno-base.h seem to be pretty much standard---at least Windows and most Unices share them---with the exception of EAGAIN. I'll send a patch to NBD to standardize the set of error codes that it sends. > In theory, what error code the NBD server needs to send should be > specified by the NBD protocol. Am I right to assume that it doesn't do > that? Nope. > In any case, I'm not sure whether qemu's internal error code > should change just for NBD. Producing the right error code for the > protocol is the job of nbd_co_receive_request(). Ok, so it shouldn't reach blk_check_request at all. But then, we should aim at making blk_check_request's checks assertions. >>> and it wouldn't even take effect for the qcow2 case >>> where we're writing past EOF only on the protocol layer. The second is >>> that -ENOSPC is only for writes and not for reads. >> >> This is right. >> >> Reads in the kernel return 0, but in QEMU we do not want that. The code >> currently returns -EIO, but perhaps -EINVAL is a better match. It also >> happens to be what Linux returns for discards. > > Perhaps it is, yes. It shouldn't make a difference for guests anyway. > (Unlike -ENOSPC for writes, which would trigger werror=enospc! That's > most likely not what we want.) Yes, we want the check duplicated in all BlockBackend users. Most of them already do it, see the work that Markus did last year I think. Paolo
