xfs: add log attributes for log lsn and grant head data

Create log attributes to export the current runtime state of the log to
sysfs. Note that the filesystem should be frozen for consistency across
attributes.

The following per-mount attributes are created: log_head_lsn,
log_tail_lsn, reserve_grant_head and write_grant_head. These represent
the physical log head, tail and reserve and write grant heads
respectively. Attribute values are exported in the following format:

	"cycle:[block,byte]"

... where cycle represents the log cycle and [block,bytes] represents
either the basic block or byte offset of the log, depending on the
attribute.  Log sequence number (LSN) values are encoded in basic blocks
and grant heads are encoded in bytes. All values are in decimal format.

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

fs/xfs/xfs_sysfs.c

@@ -53,7 +53,71 @@ struct kobj_type xfs_mp_ktype = {
 
 /* xlog */
 
+STATIC ssize_t
+log_head_lsn_show(
+	char	*buf,
+	void	*data)
+{
+	struct xlog *log = data;
+	int cycle;
+	int block;
+
+	spin_lock(&log->l_icloglock);
+	cycle = log->l_curr_cycle;
+	block = log->l_curr_block;
+	spin_unlock(&log->l_icloglock);
+
+	return snprintf(buf, PAGE_SIZE, "%d:%d\n", cycle, block);
+}
+XFS_SYSFS_ATTR_RO(log_head_lsn);
+
+STATIC ssize_t
+log_tail_lsn_show(
+	char	*buf,
+	void	*data)
+{
+	struct xlog *log = data;
+	int cycle;
+	int block;
+
+	xlog_crack_atomic_lsn(&log->l_tail_lsn, &cycle, &block);
+	return snprintf(buf, PAGE_SIZE, "%d:%d\n", cycle, block);
+}
+XFS_SYSFS_ATTR_RO(log_tail_lsn);
+
+STATIC ssize_t
+reserve_grant_head_show(
+	char	*buf,
+	void	*data)
+{
+	struct xlog *log = data;
+	int cycle;
+	int bytes;
+
+	xlog_crack_grant_head(&log->l_reserve_head.grant, &cycle, &bytes);
+	return snprintf(buf, PAGE_SIZE, "%d:%d\n", cycle, bytes);
+}
+XFS_SYSFS_ATTR_RO(reserve_grant_head);
+
+STATIC ssize_t
+write_grant_head_show(
+	char	*buf,
+	void	*data)
+{
+	struct xlog *log = data;
+	int cycle;
+	int bytes;
+
+	xlog_crack_grant_head(&log->l_write_head.grant, &cycle, &bytes);
+	return snprintf(buf, PAGE_SIZE, "%d:%d\n", cycle, bytes);
+}
+XFS_SYSFS_ATTR_RO(write_grant_head);
+
 static struct attribute *xfs_log_attrs[] = {
+	ATTR_LIST(log_head_lsn),
+	ATTR_LIST(log_tail_lsn),
+	ATTR_LIST(reserve_grant_head),
+	ATTR_LIST(write_grant_head),
 	NULL,
 };