xfs: add xlog sysfs kobject and attribute handlers

Embed a kobject into the xfs log data structure (xlog). This creates a
'log' subdirectory for every XFS mount instance in sysfs. The lifecycle
of the log kobject is tied to the lifecycle of the log.

Also define a set of generic attribute handlers associated with the log
kobject in preparation for the addition of attributes.

Signed-off-by: Brian Foster <bfoster@redhat.com>
Reviewed-by: Dave Chinner <dchinner@redhat.com>
Signed-off-by: Dave Chinner <david@fromorbit.com>

diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
index 7647818..149a4a5 100644
--- a/fs/xfs/xfs_log.c
+++ b/fs/xfs/xfs_log.c
@@ -34,6 +34,7 @@
 #include "xfs_trace.h"
 #include "xfs_fsops.h"
 #include "xfs_cksum.h"
+#include "xfs_sysfs.h"
 
 kmem_zone_t	*xfs_log_ticket_zone;
 
@@ -707,6 +708,11 @@
 		}
 	}
 
+	error = xfs_sysfs_init(&mp->m_log->l_kobj, &xfs_log_ktype, &mp->m_kobj,
+			       "log");
+	if (error)
+		goto out_destroy_ail;
+
 	/* Normal transactions can now occur */
 	mp->m_log->l_flags &= ~XLOG_ACTIVE_RECOVERY;
 
@@ -947,6 +953,9 @@
 	xfs_log_quiesce(mp);
 
 	xfs_trans_ail_destroy(mp);
+
+	xfs_sysfs_del(&mp->m_log->l_kobj);
+
 	xlog_dealloc_log(mp->m_log);
 }