I am not sure if this is a problem with all samba-4, I have only tested samba-4.2.0.
If you enable the cups USE flag, the backend gets built as /usr/bin/smbspool. But net-print/cups-2.0.2-r2 does not find it:
Printer status: Paused - "Backend /usr/libexec/cups/backend/smb does not exist!"
It can be fixed easily by symlinking it, and it will work again:
ln -s /usr/bin/smbspool /usr/libexec/cups/backend/smb
Steps to Reproduce:
1. USE="cups" emerge samba
Samba-4 cups backend not found by cups.
Samba-4 cups backend found by cups.
With the stabilization of samba-4.2.9, I got hit by this bug, so I can confirm it. Grumpily I wonder why samba-4.2.9 was stabilized with this 9-month old bug still unfixed, as the fix seems to be easy, given that the provided workaround works well. (One should resume the affected printers in the CUPS web interface after creating the symlink.)
Author: Lars Wendler <firstname.lastname@example.org>
Date: Wed Mar 30 16:00:41 2016
net-fs/samba: Fixed smb backend detection by cups (bug #552310)
Signed-off-by: Lars Wendler <email@example.com>
Sorry. I completely missed that bug. Most likely because I don't use any printers via samba. Should be fixed now. Please re-sync your portage tree and re-emerge samba-4.2.9
*** Bug 554106 has been marked as a duplicate of this bug. ***