Am 02.02.2015 um 02:19 hat Wen Congyang geschrieben: > On 01/30/2015 09:39 PM, Kevin Wolf wrote: > > Am 30.01.2015 um 09:07 hat Wen Congyang geschrieben: > >> If the child touches qiov->iov, it will cause unexpected results. > >> > >> Signed-off-by: Wen Congyang <we...@cn.fujitsu.com> > > > > Any specific child you're thinking of? > > > > I think children are not supposed to modify their qiov (which would also > > fail for init_external qiovs). Perhaps we should have made it const. > > NBD client. The qiov will be modified in iov_send_recv(): > nbd_co_writev() > nbd_client_session_co_writev() > nbd_co_writev_1() > nbd_co_send_request() > qemu_co_sendv() > qemu_co_sendv_recvv() > iov_send_recv()
Paolo, I think it's rather surprising that iov_send_recv() modifies its iov. The modification is undone at the end, so you seem to have considered that a caller might be reusing it after and you can't "use it up", but we still get problems with concurrent accesses. Was it an intentional design decision that iov_send_recv() is the sole owner of the iov and the caller must duplicate it if it's used elsewhere concurrently? Otherwise I would suggest to fix iov_send_recv(), and possibly try and make all the qiov/iov arguments in the block layer const. Kevin
