[Buildroot] [PATCH 1/1] package/busybox: update S10mdev

[Buildroot] [PATCH 1/1] package/busybox: update S10mdev

[Titouan Christophe]

Avoid race conditions in mdev invocations
* use the uevent daemon if possible
* fallback to hotplug (as before) and initialize /dev/mdev.seq
* otherwise print an error message and do nothing else

Signed-off-by: Titouan Christophe <titouan.christophe@railnova.eu>
---
 package/busybox/S10mdev | 66 +++++++++++++++++++++++++++++++++++------
 1 file changed, 57 insertions(+), 9 deletions(-)

diff --git a/package/busybox/S10mdev b/package/busybox/S10mdev
index 7075b77016..f1a836da32 100644
--- a/package/busybox/S10mdev
+++ b/package/busybox/S10mdev
@@ -1,20 +1,68 @@
 #!/bin/sh
 #
-# Start mdev....
+# Start mdev, using the uevent daemon whereas possible
 #
 
-case "$1" in
-  start)
-	echo "Starting mdev..."
-	echo /sbin/mdev >/proc/sys/kernel/hotplug
+DAEMON="uevent"
+PIDFILE="/var/run/$DAEMON.pid"
+
+has_uevent_and_netlink() {
+	[ -f /proc/net/netlink ] && [ -x /sbin/uevent ]
+}
+
+has_hotplug() {
+	[ -w /proc/sys/kernel/hotplug ]
+}
+
+
+start() {
+	if has_uevent_and_netlink; then
+		echo -n "Starting mdev within uevent... "
+		start-stop-daemon -S -b -m -p $PIDFILE -x /sbin/uevent -- /sbin/mdev
+		[ $? -eq 0 ] && echo "OK" || echo "FAIL"
+	elif has_hotplug; then
+		echo "Installing mdev as hotplug helper"
+		# Initialize the seq counter to prevent plug/unplug races
+		touch /dev/mdev.seq
+		echo /sbin/mdev > /proc/sys/kernel/hotplug
+	else
+		echo "ERROR: neither netlink+uevent nor hotplug are available"
+		echo "       Unable to start mdev !"
+		exit 1
+	fi
+
+	# Run boot time /sys scan
 	/sbin/mdev -s
+
 	# coldplug modules
 	find /sys/ -name modalias -print0 | xargs -0 sort -u | tr '\n' '\0' | \
 	    xargs -0 modprobe -abq
-	;;
-  stop)
-	;;
-  restart|reload)
+}
+
+stop() {
+	if has_uevent_and_netlink; then
+		echo -n "Stopping mdev within uevent... "
+		start-stop-daemon -K -p $PIDFILE
+		[ $? -eq 0 ] && echo "OK" || echo "FAIL"
+	elif has_hotplug; then
+		echo "Uninstalling mdev from hotplug helper"
+		echo > /proc/sys/kernel/hotplug
+	else
+		echo "ERROR: neither netlink+uevent nor hotplug are available"
+		echo "       Unable to stop mdev !"
+		exit 1
+	fi
+}
+
+restart() {
+	stop
+	start
+}
+
+
+case "$1" in
+  start|stop|restart)
+	$1
 	;;
   *)
 	echo "Usage: $0 {start|stop|restart}"
-- 
2.21.0

[Buildroot] [PATCH 1/1] package/busybox: update S10mdev

[Andy Shevchenko]

> On Wed, May 29, 2019 at 04:25:28PM +0200, Titouan Christophe wrote:
> > Avoid race conditions in mdev invocations
> > * use the uevent daemon if possible
> > * fallback to hotplug (as before) and initialize /dev/mdev.seq
> > * otherwise print an error message and do nothing else

> Thanks!
> 
> Tested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> 
> What are we going to do with this?
> As of today Buildroot can not be used with mdev in current state.

-- 
With Best Regards,
Andy Shevchenko

[Buildroot] [PATCH 1/1] package/busybox: update S10mdev

[Titouan Christophe]

Hello Andy,

Thank you for following up !

On 6/14/19 7:26 PM, Andy Shevchenko wrote:
> On Wed, May 29, 2019 at 04:25:28PM +0200, Titouan Christophe wrote:
>> Avoid race conditions in mdev invocations
>> * use the uevent daemon if possible
>> * fallback to hotplug (as before) and initialize /dev/mdev.seq
>> * otherwise print an error message and do nothing else
>>
> 
> Thanks!
> 
> Tested-by: Andy Shevchenko <andriy.shevchenko@intel.com>
> 
> What are we going to do with this?
> As of today Buildroot can not be used with mdev in current state.

In the meantime Busybox did introduce the daemon mode for mdev, which 
renders this patch obsolete (see the thread "linux: enable UEVENT_HELPER 
when mdev is used" over there 
http://lists.busybox.net/pipermail/buildroot/2019-June/251744.html).

I discussed this with Arnout on IRC, and the outcome is that we will 
adapt the S10mdev script to use the new daemon mode as soon as the next 
Busybox release is available.

In the meantime, I guess the best option is to keep this patched script 
out of tree (this is what I'm doing right now).

Best regards,

Titouan

> 
>> Signed-off-by: Titouan Christophe <titouan.christophe@railnova.eu>
>> ---
>>   package/busybox/S10mdev | 66 +++++++++++++++++++++++++++++++++++------
>>   1 file changed, 57 insertions(+), 9 deletions(-)
>>
>> diff --git a/package/busybox/S10mdev b/package/busybox/S10mdev
>> index 7075b77016..f1a836da32 100644
>> --- a/package/busybox/S10mdev
>> +++ b/package/busybox/S10mdev
>> @@ -1,20 +1,68 @@
>>   #!/bin/sh
>>   #
>> -# Start mdev....
>> +# Start mdev, using the uevent daemon whereas possible
>>   #
>>   
>> -case "$1" in
>> -  start)
>> -	echo "Starting mdev..."
>> -	echo /sbin/mdev >/proc/sys/kernel/hotplug
>> +DAEMON="uevent"
>> +PIDFILE="/var/run/$DAEMON.pid"
>> +
>> +has_uevent_and_netlink() {
>> +	[ -f /proc/net/netlink ] && [ -x /sbin/uevent ]
>> +}
>> +
>> +has_hotplug() {
>> +	[ -w /proc/sys/kernel/hotplug ]
>> +}
>> +
>> +
>> +start() {
>> +	if has_uevent_and_netlink; then
>> +		echo -n "Starting mdev within uevent... "
>> +		start-stop-daemon -S -b -m -p $PIDFILE -x /sbin/uevent -- /sbin/mdev
>> +		[ $? -eq 0 ] && echo "OK" || echo "FAIL"
>> +	elif has_hotplug; then
>> +		echo "Installing mdev as hotplug helper"
>> +		# Initialize the seq counter to prevent plug/unplug races
>> +		touch /dev/mdev.seq
>> +		echo /sbin/mdev > /proc/sys/kernel/hotplug
>> +	else
>> +		echo "ERROR: neither netlink+uevent nor hotplug are available"
>> +		echo "       Unable to start mdev !"
>> +		exit 1
>> +	fi
>> +
>> +	# Run boot time /sys scan
>>   	/sbin/mdev -s
>> +
>>   	# coldplug modules
>>   	find /sys/ -name modalias -print0 | xargs -0 sort -u | tr '\n' '\0' | \
>>   	    xargs -0 modprobe -abq
>> -	;;
>> -  stop)
>> -	;;
>> -  restart|reload)
>> +}
>> +
>> +stop() {
>> +	if has_uevent_and_netlink; then
>> +		echo -n "Stopping mdev within uevent... "
>> +		start-stop-daemon -K -p $PIDFILE
>> +		[ $? -eq 0 ] && echo "OK" || echo "FAIL"
>> +	elif has_hotplug; then
>> +		echo "Uninstalling mdev from hotplug helper"
>> +		echo > /proc/sys/kernel/hotplug
>> +	else
>> +		echo "ERROR: neither netlink+uevent nor hotplug are available"
>> +		echo "       Unable to stop mdev !"
>> +		exit 1
>> +	fi
>> +}
>> +
>> +restart() {
>> +	stop
>> +	start
>> +}
>> +
>> +
>> +case "$1" in
>> +  start|stop|restart)
>> +	$1
>>   	;;
>>     *)
>>   	echo "Usage: $0 {start|stop|restart}"
> 

[Buildroot] [PATCH 1/1] package/busybox: update S10mdev

[Peter Korsgaard]

>>>>> "Titouan" == Titouan Christophe <titouan.christophe@railnova.eu> writes:

Hi,

 > In the meantime Busybox did introduce the daemon mode for mdev, which
 > renders this patch obsolete (see the thread "linux: enable
 > UEVENT_HELPER when mdev is used" over there
 > http://lists.busybox.net/pipermail/buildroot/2019-June/251744.html).

 > I discussed this with Arnout on IRC, and the outcome is that we will
 > adapt the S10mdev script to use the new daemon mode as soon as the
 > next Busybox release is available.

Busybox 1.31.0 was released last week with this new daemon option:

https://busybox.net/

-- 
Bye, Peter Korsgaard

[Buildroot] [PATCH 1/1] package/busybox: update S10mdev

[Titouan Christophe]

Hello Peter,

On 6/18/19 9:33 PM, Peter Korsgaard wrote:
>>>>>> "Titouan" == Titouan Christophe <titouan.christophe@railnova.eu> writes:
> 
> Hi,
> 
>   > In the meantime Busybox did introduce the daemon mode for mdev, which
>   > renders this patch obsolete (see the thread "linux: enable
>   > UEVENT_HELPER when mdev is used" over there
>   > http://lists.busybox.net/pipermail/buildroot/2019-June/251744.html).
> 
>   > I discussed this with Arnout on IRC, and the outcome is that we will
>   > adapt the S10mdev script to use the new daemon mode as soon as the
>   > next Busybox release is available.
> 
> Busybox 1.31.0 was released last week with this new daemon option:
> 
> https://busybox.net/


Thank you for the heads up.

I submitted a patch series for the aforementioned changes, see 
http://patchwork.ozlabs.org/project/buildroot/list/?series=114874

Best regards,

Titouan