[Cluster-devel] [RFC] gfs2: Add sb and rgrp fields to aid fsck and grow

[Andrew Price]

This adds some fields to the superblock and resource group header
structures that we can use in rg size and address discovery in gfs2_grow
and fsck.gfs2. They are not intended to be changed after mkfs time.

sb_rgsize is the base resource group size used by mkfs.gfs2, before any
adjustment or alignment. It is required in order to extend the fs with
the correct resource group size in gfs2_grow and can also be used by
fsck.gfs2 when rebuilding broken resource groups.

rg_next is the address of the next resource group and is set by
mkfs.gfs2. It is intended to be used as a hint to fsck.gfs2 and can be
used by other tools which need to read the resource groups sequentially.

rg_uuid is intended to be the same as sb_uuid for the file system. It
can be used by fsck.gfs2, when searching for resource group headers, in
order to distinguish resource groups created as part of a previous file
system on the device from resource groups in the current file system.

Signed-off-by: Andrew Price <anprice at redhat.com>
---
 include/uapi/linux/gfs2_ondisk.h | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/include/uapi/linux/gfs2_ondisk.h b/include/uapi/linux/gfs2_ondisk.h
index 0f24c07..f1489cb 100644
--- a/include/uapi/linux/gfs2_ondisk.h
+++ b/include/uapi/linux/gfs2_ondisk.h
@@ -118,7 +118,8 @@ struct gfs2_sb {
 
 	__be32 sb_bsize;
 	__be32 sb_bsize_shift;
-	__u32 __pad1;	/* Was journal segment size in gfs1 */
+	__be32 sb_rgsize; /* Resource group size used on fs creation.
+	                     Was journal segment size in gfs1 */
 
 	struct gfs2_inum sb_master_dir; /* Was jindex dinode in gfs1 */
 	struct gfs2_inum __pad2; /* Was rindex dinode in gfs1 */
@@ -131,6 +132,7 @@ struct gfs2_sb {
 	struct gfs2_inum __pad4; /* Was licence inode in gfs1 */
 #define GFS2_HAS_UUID 1
 	__u8 sb_uuid[16]; /* The UUID, maybe 0 for backwards compat */
+
 };
 
 /*
@@ -188,8 +190,10 @@ struct gfs2_rgrp {
 	__be32 rg_dinodes;
 	__be32 __pad;
 	__be64 rg_igeneration;
+	__be64 rg_next; /* Address of the next resource group */
+	__u8 rg_uuid[16]; /* The UUID, maybe 0 for backwards compat */
 
-	__u8 rg_reserved[80]; /* Several fields from gfs1 now reserved */
+	__u8 rg_reserved[64]; /* Several fields from gfs1 now reserved */
 };
 
 /*
-- 
1.8.3.1