udev: set clock group for PTP and RTC devices

Add a new group for clock devices to enable applications like linuxptp
to open clocks without root privileges.

README

@@ -368,7 +368,8 @@ USERS AND GROUPS:
         need to be resolvable by getgrnam() at any time, even in the very early
         boot stages, where no other databases and network are available:
 
-        audio, cdrom, dialout, disk, input, kmem, kvm, lp, render, tape, tty, video
+        audio, cdrom, clock, dialout, disk, input, kmem, kvm, lp, render, tape,
+        tty, video
 
         During runtime, the journal daemon requires the "systemd-journal" system
         group to exist. New journal files will be readable by this group (but

meson.build

@@ -937,6 +937,7 @@ static_ugids = []
 foreach option : ['adm-gid',
                   'audio-gid',
                   'cdrom-gid',
+                  'clock-gid',
                   'dialout-gid',
                   'disk-gid',
                   'input-gid',

meson_options.txt

@@ -291,6 +291,8 @@ option('audio-gid', type : 'integer', value : 0,
        description : 'soft-static allocation for the "audio" group')
 option('cdrom-gid', type : 'integer', value : 0,
        description : 'soft-static allocation for the "cdrom" group')
+option('clock-gid', type : 'integer', value : 0,
+       description : 'soft-static allocation for the "clock" group')
 option('dialout-gid', type : 'integer', value : 0,
        description : 'soft-static allocation for the "dialout" group')
 option('disk-gid', type : 'integer', value : 0,

rules.d/50-udev-default.rules.in

@@ -10,6 +10,7 @@ SUBSYSTEM=="block", KERNEL=="md*", ENV{ID_IGNORE_DISKSEQ}="1"
 
 SUBSYSTEM=="virtio-ports", KERNEL=="vport*", ATTR{name}=="?*", SYMLINK+="virtio-ports/$attr{name}"
 
+SUBSYSTEM=="rtc", GROUP="clock", MODE="0660"
 # select "system RTC" or just use the first one
 SUBSYSTEM=="rtc", ATTR{hctosys}=="1", SYMLINK+="rtc"
 SUBSYSTEM=="rtc", KERNEL=="rtc0", SYMLINK+="rtc", OPTIONS+="link_priority=-100"
@@ -30,6 +31,7 @@ SUBSYSTEM=="pci|usb|platform", IMPORT{builtin}="path_id"
 
 SUBSYSTEM=="net", IMPORT{builtin}="net_driver"
 
+SUBSYSTEM=="ptp", GROUP="clock", MODE="0660"
 SUBSYSTEM=="ptp", ATTR{clock_name}=="KVM virtual PTP", SYMLINK+="ptp_kvm"
 SUBSYSTEM=="ptp", ATTR{clock_name}=="hyperv", SYMLINK+="ptp_hyperv"
 

sysusers.d/basic.conf.in

@@ -25,6 +25,7 @@ g utmp    {{UTMP_GID   }}     -            -
 # Physical and virtual hardware access groups
 g audio   {{AUDIO_GID  }}     -            -
 g cdrom   {{CDROM_GID  }}     -            -
+g clock   {{CLOCK_GID  }}     -            -
 g dialout {{DIALOUT_GID}}     -            -
 g disk    {{DISK_GID   }}     -            -
 g input   {{INPUT_GID  }}     -            -