cleanup udev part of README.devices, reflect split rules

Remove vague statements from the README. On all current distributions,
the udev paths are identical, anyone deliberately deviating from the
defaults should be able to handle it by themselves.

Rules in /etc/udev/rules.d/ should only be used for customization, or
for locally built packages.

diff --git a/README.devices b/README.devices
index 3e0d5f2d089f6291de36d234a7813596b2b15889..ad0219a16a203e005b5777afc1ff658248bb5baa 100644 (file)
--- a/README.devices
+++ b/README.devices
@@ -213,33 +213,39 @@ For USB-to-serial based devices, we recommended using our udev rules file
 (see below for details).
 
 
-Permissions for USB devices (udev rules file)
----------------------------------------------
+Permissions for USB devices (udev rules files)
+----------------------------------------------
 
 When using USB-based devices supported by libsigrok, the user running the
 libsigrok frontend (e.g. sigrok-cli) has to have (read/write) permissions
 for the respective USB device.
 
-On Linux, this is accomplished using either 'chmod' (not recommended) or
-using the udev rules file shipped with libsigrok (recommended).
+On Linux, this is accomplished using udev rules. libsigrok ships a rules
+file containing all supported devices which can be detected reliably
+(generic USB-to-serial converters are omitted, as these are used for a wide
+range of devices, e.g. GPS receivers, which are not handled by libsigrok).
 
-The file is available in contrib/z60_libsigrok.rules. It contains entries
-for all libsigrok-supported (USB-based) devices and changes their group
-to 'plugdev' and the permissions to '664'.
+The file is available in contrib/60-libsigrok.rules. This file just contains
+the list of devices and flags these devices with ID_SIGROK="1". Access is
+granted by the 61-libsigrok-plugdev.rules or 61-libsigrok-uaccess.rules files,
+allowing access to members of the plugdev group or to currently logged in
+users, respectively.
 
 When using a libsigrok package from your favorite Linux distribution, the
-packager will have already taken care of properly installing the udev file
-in the correct (distro-specific) place, and you don't have to do anything.
-The packager might also have adapted 'plugdev' and '664' as needed.
+files should already be installed in /usr/lib/udev/rules.d/, i.e.
+60-libsigrok.rules and one of the access granting rules files. Use of
+61-libsigrok-uaccess.rules is encouraged on systemd distributions.
+
+The access policy can be locally overridden by placing appropriate rules in
+/etc/udev/rules.d/, disabling or ammending the default policy. See the
+udev documentation, e.g. man 7 udev, for details.
 
 If you're building from source, you need to copy the file to the place
-where your distro expects such files. This is beyond the scope of this README,
-but generally the location could be e.g. /etc/udev/rules.d, or maybe
-/lib/udev/rules.d, or something else. Afterwards you might have to restart
-udev, e.g. via '/etc/init.d/udev restart' or similar, and you'll have to
-re-attach your device via USB.
+where udev will read these rules. Local rules should go to /etc/udev/rules.d.
+Keep the file naming, otherwise interaction between the libsigrok rules and
+rules shipped by the system will be broken.
 
-Please consult the udev docs of your distro for details.
+Please consult the udev docs for details.
 
 
 Cypress FX2 based devices