[PATCH] sysfs and driver core: add callback helper, used by SCSI and S390

This patch (as868) adds a helper routine for device drivers that need
to set up a callback to perform some action in a different process's
context.  This is intended for use by attribute methods that want to
unregister themselves or their parent device.  Attribute method calls
are mutually exclusive with unregistration, so such actions cannot be
taken directly.

Two attribute methods are converted to use the new helper routine: one
for SCSI device deletion and one for System/390 ccwgroup devices.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Cc: Hugh Dickins <hugh@veritas.com>
Cc: Cornelia Huck <cornelia.huck@de.ibm.com>
Cc: Oliver Neukum <oneukum@suse.de>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 15 insertions, 3 deletions

diff --git a/drivers/s390/cio/ccwgroup.c b/drivers/s390/cio/ccwgroup.c
index d48e3ca4752c..5aeb68e732b0 100644
--- a/drivers/s390/cio/ccwgroup.c
+++ b/drivers/s390/cio/ccwgroup.c
@@ -71,19 +71,31 @@ __ccwgroup_remove_symlinks(struct ccwgroup_device *gdev)
  * Provide an 'ungroup' attribute so the user can remove group devices no
  * longer needed or accidentially created. Saves memory :)
  */
+static void ccwgroup_ungroup_callback(struct device *dev)
+{
+	struct ccwgroup_device *gdev = to_ccwgroupdev(dev);
+
+	__ccwgroup_remove_symlinks(gdev);
+	device_unregister(dev);
+}
+
 static ssize_t
 ccwgroup_ungroup_store(struct device *dev, struct device_attribute *attr, const char *buf, size_t count)
 {
 	struct ccwgroup_device *gdev;
+	int rc;
 
 	gdev = to_ccwgroupdev(dev);
 
 	if (gdev->state != CCWGROUP_OFFLINE)
 		return -EINVAL;
 
-	__ccwgroup_remove_symlinks(gdev);
-	device_unregister(dev);
-
+	/* Note that we cannot unregister the device from one of its
+	 * attribute methods, so we have to use this roundabout approach.
+	 */
+	rc = device_schedule_callback(dev, ccwgroup_ungroup_callback);
+	if (rc)
+		count = rc;
 	return count;
 }