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 <[e-mail]>
Reviewed-by: Dave Chinner <[e-mail]>
Signed-off-by: Dave Chinner <[e-mail]>

fs/xfs/xfs_log.c

···
 #include "xfs_trace.h"
 #include "xfs_fsops.h"
 #include "xfs_cksum.h"
+#include "xfs_sysfs.h"
 
 kmem_zone_t	*xfs_log_ticket_zone;
 
···
 		}
 	}
 
+	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;
 
···
 	xfs_log_quiesce(mp);
 
 	xfs_trans_ail_destroy(mp);
+
+	xfs_sysfs_del(&mp->m_log->l_kobj);
+
 	xlog_dealloc_log(mp->m_log);
 }
 

fs/xfs/xfs_log_priv.h

···
 	struct xlog_grant_head	l_reserve_head;
 	struct xlog_grant_head	l_write_head;
 
+	struct xfs_kobj		l_kobj;
+
 	/* The following field are used for debugging; need to hold icloglock */
 #ifdef DEBUG
 	char			*l_iclog_bak[XLOG_MAX_ICLOGS];

fs/xfs/xfs_sysfs.c

···
 
 #include "xfs.h"
 #include "xfs_sysfs.h"
+#include "xfs_log_format.h"
+#include "xfs_log.h"
+#include "xfs_log_priv.h"
 
 struct xfs_sysfs_attr {
 	struct attribute attr;
···
 
 struct kobj_type xfs_mp_ktype = {
 	.release = xfs_sysfs_release,
+};
+
+/* xlog */
+
+static struct attribute *xfs_log_attrs[] = {
+	NULL,
+};
+
+static inline struct xlog *
+to_xlog(struct kobject *kobject)
+{
+	struct xfs_kobj *kobj = to_kobj(kobject);
+	return container_of(kobj, struct xlog, l_kobj);
+}
+
+STATIC ssize_t
+xfs_log_show(
+	struct kobject		*kobject,
+	struct attribute	*attr,
+	char			*buf)
+{
+	struct xlog *log = to_xlog(kobject);
+	struct xfs_sysfs_attr *xfs_attr = to_attr(attr);
+
+	return xfs_attr->show ? xfs_attr->show(buf, log) : 0;
+}
+
+STATIC ssize_t
+xfs_log_store(
+	struct kobject		*kobject,
+	struct attribute	*attr,
+	const char		*buf,
+	size_t			count)
+{
+	struct xlog *log = to_xlog(kobject);
+	struct xfs_sysfs_attr *xfs_attr = to_attr(attr);
+
+	return xfs_attr->store ? xfs_attr->store(buf, count, log) : 0;
+}
+
+static struct sysfs_ops xfs_log_ops = {
+	.show = xfs_log_show,
+	.store = xfs_log_store,
+};
+
+struct kobj_type xfs_log_ktype = {
+	.release = xfs_sysfs_release,
+	.sysfs_ops = &xfs_log_ops,
+	.default_attrs = xfs_log_attrs,
 };

fs/xfs/xfs_sysfs.h

···
 #define __XFS_SYSFS_H__
 
 extern struct kobj_type xfs_mp_ktype;	/* xfs_mount */
+extern struct kobj_type xfs_log_ktype;	/* xlog */
 
 static inline struct xfs_kobj *
 to_kobj(struct kobject *kobject)