[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, 29 insertions, 0 deletions

diff --git a/drivers/base/core.c b/drivers/base/core.c
index f191afe62b4d..ad0f4a2f25c4 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -407,6 +407,35 @@ void device_remove_bin_file(struct device *dev, struct bin_attribute *attr)
 }
 EXPORT_SYMBOL_GPL(device_remove_bin_file);
 
+/**
+ * device_schedule_callback - helper to schedule a callback for a device
+ * @dev: device.
+ * @func: callback function to invoke later.
+ *
+ * Attribute methods must not unregister themselves or their parent device
+ * (which would amount to the same thing).  Attempts to do so will deadlock,
+ * since unregistration is mutually exclusive with driver callbacks.
+ *
+ * Instead methods can call this routine, which will attempt to allocate
+ * and schedule a workqueue request to call back @func with @dev as its
+ * argument in the workqueue's process context.  @dev will be pinned until
+ * @func returns.
+ *
+ * Returns 0 if the request was submitted, -ENOMEM if storage could not
+ * be allocated.
+ *
+ * NOTE: This routine won't work if CONFIG_SYSFS isn't set!  It uses an
+ * underlying sysfs routine (since it is intended for use by attribute
+ * methods), and if sysfs isn't available you'll get nothing but -ENOSYS.
+ */
+int device_schedule_callback(struct device *dev,
+                void (*func)(struct device *))
+{
+        return sysfs_schedule_callback(&dev->kobj,
+                        (void (*)(void *)) func, dev);
+}
+EXPORT_SYMBOL_GPL(device_schedule_callback);
+
 static void klist_children_get(struct klist_node *n)
 {
         struct device *dev = container_of(n, struct device, knode_parent);