Commit 0210b66d authored May 23, 2009 by Stefan Richter

firewire: core: add sysfs attribute for easier udev rules



This adds the attribute /sys/bus/firewire/devices/fw[0-9]+/units.  It
can be used in udev rules like the following ones:

# IIDC devices: industrial cameras and some webcams
SUBSYSTEM=="firewire", ATTR{units}=="*0x00a02d:0x00010?*", GROUP="video"

# AV/C devices: camcorders, set-top boxes, TV sets, audio devices, ...
SUBSYSTEM=="firewire", ATTR{units}=="*0x00a02d:0x010001*", GROUP="video"

Background:

firewire-core manages two device types:
  - fw_device is a FireWire node.  A character device file is associated
    with it.
  - fw_unit is a unit directory on a node.  Each fw_device may have 0..n
    children of type fw_unit.  The units tell us what kinds of protocols
    a node implements.

We want to set ownership or ACLs or permissions of the character device
file of an fw_device, or/and create symlinks to it, based on available
protocols.  Until now udev rules had to look at the fw_unit devices and
then modify their parent's character device file accordingly.  This is
problematic for two reasons:  1) It happens sometime after the creation
of the fw_device, 2) an access policy may require that information from
all children is evaluated before a decision about the parent is made.

Problem 1) can ultimately not be avoided since this is the nature of
FireWire nodes:  They may add or remove unit directories at any point in
time.

However, we can still help userland a lot by providing the protocol type
information of all units in a summary sysfs attribute directly at the
fw_device.  This way,
   - the information is immediately available at the affected device
     when userspace goes about to handle an ADD or CHANGE event of the
     fw_device,
   - with most policies, it won't be necessary anymore to dig through
     child attributes.

The new attribute is called "units".  It contains space-separated tuples
of specifier_id and version of each present unit.  The delimiter within
tuples is a colon.  Specifier_id and version are printed as 0x%06x.

Here is an example of a node which implements an IPv4 unit and an IPv6
unit:  $ cat /sys/bus/firewire/devices/fw2/units
0x00005e:0x000001 0x00005e:0x000002

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>

parent e5333db9

drivers/firewire/fw-device.c

+50 −0

Original line number	Diff line number	Diff line
		@@ -355,9 +355,56 @@ static ssize_t guid_show(struct device *dev,
		return ret;
		}

		static int units_sprintf(char buf, u32 directory)
		{
		struct fw_csr_iterator ci;
		int key, value;
		int specifier_id = 0;
		int version = 0;

		fw_csr_iterator_init(&ci, directory);
		while (fw_csr_iterator_next(&ci, &key, &value)) {
		switch (key) {
		case CSR_SPECIFIER_ID:
		specifier_id = value;
		break;
		case CSR_VERSION:
		version = value;
		break;
		}
		}

		return sprintf(buf, "0x%06x:0x%06x ", specifier_id, version);
		}

		static ssize_t units_show(struct device *dev,
		struct device_attribute attr, char buf)
		{
		struct fw_device *device = fw_device(dev);
		struct fw_csr_iterator ci;
		int key, value, i = 0;

		down_read(&fw_device_rwsem);
		fw_csr_iterator_init(&ci, &device->config_rom[5]);
		while (fw_csr_iterator_next(&ci, &key, &value)) {
		if (key != (CSR_UNIT \| CSR_DIRECTORY))
		continue;
		i += units_sprintf(&buf[i], ci.p + value - 1);
		if (i >= PAGE_SIZE - (8 + 1 + 8 + 1))
		break;
		}
		up_read(&fw_device_rwsem);

		if (i)
		buf[i - 1] = '\n';

		return i;
		}

		static struct device_attribute fw_device_attributes[] = {
		__ATTR_RO(config_rom),
		__ATTR_RO(guid),
		__ATTR_RO(units),
		__ATTR_NULL,
		};

		@@ -1000,6 +1047,9 @@ static void fw_device_refresh(struct work_struct *work)

		create_units(device);

		/* Userspace may want to re-read attributes. */
		kobject_uevent(&device->device.kobj, KOBJ_CHANGE);

		if (atomic_cmpxchg(&device->state,
		FW_DEVICE_INITIALIZING,
		FW_DEVICE_RUNNING) == FW_DEVICE_GONE)

drivers/firewire/fw-device.h

+1 −1

Original line number	Diff line number	Diff line
		@@ -42,7 +42,7 @@ enum fw_device_state {
		struct fw_attribute_group {
		struct attribute_group *groups[2];
		struct attribute_group group;
		struct attribute *attrs[11];
		struct attribute *attrs[12];
		};

		struct fw_node;

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