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Sometimes other drivers depend on particular configfs items. For example, ocfs2 mounts depend on a heartbeat region item. If that region item is removed with rmdir(2), the ocfs2 mount must BUG or go readonly. Not happy. This provides two additional API calls: configfs_depend_item() and configfs_undepend_item(). A client driver can call configfs_depend_item() on an existing item to tell configfs that it is depended on. configfs will then return -EBUSY from rmdir(2) for that item. When the item is no longer depended on, the client driver calls configfs_undepend_item() on it. These API cannot be called underneath any configfs callbacks, as they will conflict. They can block and allocate. A client driver probably shouldn't calling them of its own gumption. Rather it should be providing an API that external subsystems call. How does this work? Imagine the ocfs2 mount process. When it mounts, it asks for a heart region item. This is done via a call into the heartbeat code. Inside the heartbeat code, the region item is looked up. Here, the heartbeat code calls configfs_depend_item(). If it succeeds, then heartbeat knows the region is safe to give to ocfs2. If it fails, it was being torn down anyway, and heartbeat can gracefully pass up an error. [ Fixed some bad whitespace in configfs.txt. --Mark ] Signed-off-by: Joel Becker <joel.becker@oracle.com> Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com> |
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