sane-backends: rebind printers to usblp after scan

While scanning, sane unbinds usb device from usblp module. This
patch creates a saned wrapper that keep track of all usb devices
binded to usblp before saned is launched and rebind them back
if not still bound after saned exits.

This workaround is only effective if saned is launched by a super
daemon like xinetd as it needs to exit after scan job finish. If
not, printing will not be available while saned service is running.

Write access to /sys/bus/usb/drivers/usblp/bind is required. So,
normally it would require root access.

Signed-off-by: Luiz Angelo Daros de Luca <luizluca@gmail.com>

2 files changed, 24 insertions, 0 deletions

diff --git a/utils/sane-backends/files/xinet.d_sane-port b/utils/sane-backends/files/etc/xinetd.d/sane-port
index 9119973f6..9119973f6 100644
--- a/utils/sane-backends/files/xinet.d_sane-port
+++ b/utils/sane-backends/files/etc/xinetd.d/sane-port
diff --git a/utils/sane-backends/files/usr/sbin/saned b/utils/sane-backends/files/usr/sbin/saned
new file mode 100755
index 000000000..711492633
--- /dev/null
+++ b/utils/sane-backends/files/usr/sbin/saned
@@ -0,0 +1,24 @@
+#!/bin/sh
+
+usblp_driver="/sys/bus/usb/drivers/usblp"
+
+inuse=""
+if [ -e /sys/bus/usb/devices ]; then
+	for usbdev_driver in /sys/bus/usb/devices/*/driver; do
+		[ -e "$usbdev_driver" ] || continue
+		[ "$(readlink -f "$usbdev_driver")" = "$usblp_driver" ] || continue
+		usbdev="${usbdev_driver%/*}"
+		inuse="$inuse ${usbdev##*/}"
+	done
+fi
+
+/usr/lib/sane/saned "$@"
+err=$?
+
+for usbdev in $inuse; do
+	[ -e "/sys/bus/usb/devices/$usbdev/driver" ] && continue
+	logger -t saned "binding device $usbdev back to usblp..."
+	printf '%s' "$usbdev" > "$usblp_driver/bind"
+done
+
+exit $err