xfs: introduce metadata IO error class

Now we have the basic infrastructure, add the first error class so
we can build up the infrastructure in a meaningful way. Add the
metadata async write IO error class and sysfs entry, and introduce a
default configuration that matches the existing "retry forever"
behavior for async write metadata buffers.

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

diff --git a/fs/xfs/xfs_mount.h b/fs/xfs/xfs_mount.h
index d639795..352a5c8 100644
--- a/fs/xfs/xfs_mount.h
+++ b/fs/xfs/xfs_mount.h
@@ -44,9 +44,11 @@
  * Error numbers define the errors that are configurable.
  */
 enum {
+	XFS_ERR_METADATA,
 	XFS_ERR_CLASS_MAX,
 };
 enum {
+	XFS_ERR_DEFAULT,
 	XFS_ERR_ERRNO_MAX,
 };
 
@@ -146,6 +148,7 @@
 						/* low free space thresholds */
 	struct xfs_kobj		m_kobj;
 	struct xfs_kobj		m_error_kobj;
+	struct xfs_kobj		m_error_meta_kobj;
 	struct xfs_error_cfg	m_error_cfg[XFS_ERR_CLASS_MAX][XFS_ERR_ERRNO_MAX];
 	struct xstats		m_stats;	/* per-fs stats */