Commit f36776fa authored by Peter Rajnoha's avatar Peter Rajnoha Committed by Greg Kroah-Hartman
Browse files

kobject: support passing in variables for synthetic uevents 



This patch makes it possible to pass additional arguments in addition
to uevent action name when writing /sys/.../uevent attribute. These
additional arguments are then inserted into generated synthetic uevent
as additional environment variables.

Before, we were not able to pass any additional uevent environment
variables for synthetic uevents. This made it hard to identify such uevents
properly in userspace to make proper distinction between genuine uevents
originating from kernel and synthetic uevents triggered from userspace.
Also, it was not possible to pass any additional information which would
make it possible to optimize and change the way the synthetic uevents are
processed back in userspace based on the originating environment of the
triggering action in userspace. With the extra additional variables, we are
able to pass through this extra information needed and also it makes it
possible to synchronize with such synthetic uevents as they can be clearly
identified back in userspace.

The format for writing the uevent attribute is following:

    ACTION [UUID [KEY=VALUE ...]

There's no change in how "ACTION" is recognized - it stays the same
("add", "change", "remove"). The "ACTION" is the only argument required
to generate synthetic uevent, the rest of arguments, that this patch
adds support for, are optional.

The "UUID" is considered as transaction identifier so it's possible to
use the same UUID value for one or more synthetic uevents in which case
we logically group these uevents together for any userspace listeners.
The "UUID" is expected to be in "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"
format where "x" is a hex digit. The value appears in uevent as
"SYNTH_UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" environment variable.

The "KEY=VALUE" pairs can contain alphanumeric characters only. It's
possible to define zero or more more pairs - each pair is then delimited
by a space character " ". Each pair appears in synthetic uevents as
"SYNTH_ARG_KEY=VALUE" environment variable. That means the KEY name gains
"SYNTH_ARG_" prefix to avoid possible collisions with existing variables.
To pass the "KEY=VALUE" pairs, it's also required to pass in the "UUID"
part for the synthetic uevent first.

If "UUID" is not passed in, the generated synthetic uevent gains
"SYNTH_UUID=0" environment variable automatically so it's possible to
identify this situation in userspace when reading generated uevent and so
we can still make a difference between genuine and synthetic uevents.

Signed-off-by: default avatarPeter Rajnoha <prajnoha@redhat.com>
Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
parent 62655397

Documentation/ABI/testing/sysfs-uevent

0 → 100644
+47 −0
Original line number Diff line number Diff line 
What:           /sys/.../uevent

Date:           May 2017

KernelVersion:  4.12

Contact:        Linux kernel mailing list <linux-kernel@vger.kernel.org>

Description:

                Enable passing additional variables for synthetic uevents that

                are generated by writing /sys/.../uevent file.



                Recognized extended format is ACTION [UUID [KEY=VALUE ...].



                The ACTION is compulsory - it is the name of the uevent action

                ("add", "change", "remove"). There is no change compared to

                previous functionality here. The rest of the extended format

                is optional.



                You need to pass UUID first before any KEY=VALUE pairs.

                The UUID must be in "xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx"

                format where 'x' is a hex digit. The UUID is considered to be

                a transaction identifier so it's possible to use the same UUID

                value for one or more synthetic uevents in which case we

                logically group these uevents together for any userspace

                listeners. The UUID value appears in uevent as

                "SYNTH_UUID=xxxxxxxx-xxxx-xxxx-xxxx-xxxxxxxxxxxx" environment

                variable.



                If UUID is not passed in, the generated synthetic uevent gains

                "SYNTH_UUID=0" environment variable automatically.



                The KEY=VALUE pairs can contain alphanumeric characters only.

                It's possible to define zero or more pairs - each pair is then

                delimited by a space character ' '. Each pair appears in

                synthetic uevent as "SYNTH_ARG_KEY=VALUE". That means the KEY

                name gains "SYNTH_ARG_" prefix to avoid possible collisions

                with existing variables.



                Example of valid sequence written to the uevent file:



                    add fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed A=1 B=abc



                This generates synthetic uevent including these variables:



                    ACTION=add

                    SYNTH_ARG_A=1

                    SYNTH_ARG_B=abc

                    SYNTH_UUID=fe4d7c9d-b8c6-4a70-9ef1-3d8a58d18eed

Users:

                udev, userspace tools generating synthetic uevents

drivers/base/bus.c

+2 −8
Original line number Diff line number Diff line
@@ -648,10 +648,7 @@ static void remove_probe_files(struct bus_type *bus) 
static ssize_t uevent_store(struct device_driver *drv, const char *buf,

			    size_t count)

{

	enum kobject_action action;



	if (kobject_action_type(buf, count, &action) == 0)

		kobject_uevent(&drv->p->kobj, action);

	kobject_synth_uevent(&drv->p->kobj, buf, count);

	return count;

}

static DRIVER_ATTR_WO(uevent);
@@ -868,10 +865,7 @@ static void klist_devices_put(struct klist_node *n) 
static ssize_t bus_uevent_store(struct bus_type *bus,

				const char *buf, size_t count)

{

	enum kobject_action action;



	if (kobject_action_type(buf, count, &action) == 0)

		kobject_uevent(&bus->p->subsys.kobj, action);

	kobject_synth_uevent(&bus->p->subsys.kobj, buf, count);

	return count;

}

static BUS_ATTR(uevent, S_IWUSR, NULL, bus_uevent_store);

drivers/base/core.c

+2 −5
Original line number Diff line number Diff line
@@ -981,12 +981,9 @@ out: 
static ssize_t uevent_store(struct device *dev, struct device_attribute *attr,

			    const char *buf, size_t count)

{

	enum kobject_action action;

	if (kobject_synth_uevent(&dev->kobj, buf, count))

		dev_err(dev, "uevent: failed to send synthetic uevent\n");



	if (kobject_action_type(buf, count, &action) == 0)

		kobject_uevent(&dev->kobj, action);

	else

		dev_err(dev, "uevent: unknown action-string\n");

	return count;

}

static DEVICE_ATTR_RW(uevent);

include/linux/kobject.h

+1 −3
Original line number Diff line number Diff line
@@ -217,11 +217,9 @@ extern struct kobject *firmware_kobj; 
int kobject_uevent(struct kobject *kobj, enum kobject_action action);

int kobject_uevent_env(struct kobject *kobj, enum kobject_action action,

			char *envp[]);

int kobject_synth_uevent(struct kobject *kobj, const char *buf, size_t count);



__printf(2, 3)

int add_uevent_var(struct kobj_uevent_env *env, const char *format, ...);



int kobject_action_type(const char *buf, size_t count,

			enum kobject_action *type);



#endif /* _KOBJECT_H_ */

kernel/module.c

+1 −4
Original line number Diff line number Diff line
@@ -1202,10 +1202,7 @@ static ssize_t store_uevent(struct module_attribute *mattr, 
			    struct module_kobject *mk,

			    const char *buffer, size_t count)

{

	enum kobject_action action;



	if (kobject_action_type(buffer, count, &action) == 0)

		kobject_uevent(&mk->kobj, action);

	kobject_synth_uevent(&mk->kobj, buffer, count);

	return count;

}

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