[Xen-devel] Linux device naming (suggested udev rules adjustment)

["Jan Beulich" <JBeulich@xxxxxxxxxx>]

While earlier this year some work was done to eliminate libxc's
creation of nodes under /dev (as in some cases it actually got
things wrong), I just found that tapdisk2 does exactly the same.
While I'm not currently aiming at removing this code, I want to
at least suggest some adjustments to the provided rules file.

First of all, the present rule

KERNEL=="blktap[0-9]*", NAME="xen/%k"

matches both blktap1's devices and blktap2's ring devices,
resulting in whoever comes last replacing what was there
before (e.g. a tap2:aio: attach will replace bltap1's
/dev/blktap0 [i.e. the main control device] with the ring device
of the new virtual disk). Therefore we should add a subsystem
qualifier there.

Second, at some udev versions default to using 0660 as the
permissions on nodes it creates. The kernel (with devtmpfs)
defaults to 0600, and hence I'd suggest to also make this
explicit in the rules.

If this is acceptable, a patch is found below/attached.

Finally, in an attempt to overcome the warnings newer udev
versions issue when NAME= specified and kernel provided names
do not match, "xen/" prefixes were added to some device names
in the pv-ops tree. This has lead to somewhat suspicious sysfs
nodes containing exclamation marks (like "xen!evtchn"). As I
realized only recently, this can be easily avoided by using the
.devnode method of struct class, struct device_type, and struct
gendisk, as well as the .nodename member of struct miscdevice
(which will keep device_get_devnode() from converting '/' to '!').

Jan

**************** patch follows ***************

Signed-off-by: Jan Beulich <jbeulich@xxxxxxxxxx>

--- a/tools/hotplug/Linux/xen-backend.rules
+++ b/tools/hotplug/Linux/xen-backend.rules
@@ -7,6 +7,10 @@ SUBSYSTEM=="xen-backend", KERNEL=="vif-*
 SUBSYSTEM=="xen-backend", KERNEL=="vscsi*", RUN+="/etc/xen/scripts/vscsi 
$env{ACTION}"
 SUBSYSTEM=="xen-backend", ACTION=="remove", 
RUN+="/etc/xen/scripts/xen-hotplug-cleanup"
 KERNEL=="evtchn", NAME="xen/%k"
-KERNEL=="blktap[0-9]*", NAME="xen/%k"
-KERNEL=="pci_iomul", NAME="xen/%k"
+SUBSYSTEM=="xen", KERNEL=="blktap[0-9]*", NAME="xen/%k", MODE="0600"
+SUBSYSTEM=="blktap2", KERNEL=="blktap[0-9]*", NAME="xen/blktap-2/%k", 
MODE="0600"
+KERNEL=="blktap-control", NAME="xen/blktap-2/control", MODE="0600"
+KERNEL=="gntdev", NAME="xen/%k", MODE="0600"
+KERNEL=="pci_iomul", NAME="xen/%k", MODE="0600"
+KERNEL=="tapdev[a-z]*", NAME="xen/blktap-2/tapdev%m", MODE="0600"
 SUBSYSTEM=="net", KERNEL=="tap*", ACTION=="add", 
RUN+="/etc/xen/scripts/vif-setup $env{ACTION} type_if=tap"

Attachment: udev-rules.patch
Description: Text document

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