If you use a virtual Linux machine that will become an SMB client, you need to specify an option when QEMU is started. Append the following to the script that starts the virtual machine:
This option creates a fake network interface (10.0.2.4) from the host OS to the guest (VM) OS. Furthermore, SMB is enabled through this interface. The host OS should have Windows file sharing enabled.
Sadly, this option is available only to Linux-hosted QEMU and not Windows-hosted QEMU.