[rfc, patch 1/3] larger block group descriptors

make linux-2.6.16.19 use variable length block group descriptors.


Index: linux-2.6.16.19/include/linux/ext3_fs.h
===================================================================
--- linux-2.6.16.19.orig/include/linux/ext3_fs.h	2006-06-07 13:05:52.000000000 +0200
+++ linux-2.6.16.19/include/linux/ext3_fs.h	2006-06-07 13:20:26.000000000 +0200
@@ -20,7 +20,6 @@
 #include <linux/ext3_fs_i.h>
 #include <linux/ext3_fs_sb.h>
 
-
 struct statfs;
 
 /*
@@ -142,6 +141,9 @@ struct ext3_group_desc
 /*
  * Macro-instructions used to manage group descriptors
  */
+#define EXT3_MIN_DESC_SIZE		32
+#define	EXT3_MAX_DESC_SIZE		EXT3_MIN_BLOCK_SIZE
+#define EXT3_DESC_SIZE(s)		(EXT3_SB(s)->s_desc_size)
 #ifdef __KERNEL__
 # define EXT3_BLOCKS_PER_GROUP(s)	(EXT3_SB(s)->s_blocks_per_group)
 # define EXT3_DESC_PER_BLOCK(s)		(EXT3_SB(s)->s_desc_per_block)
@@ -149,7 +151,7 @@ struct ext3_group_desc
 # define EXT3_DESC_PER_BLOCK_BITS(s)	(EXT3_SB(s)->s_desc_per_block_bits)
 #else
 # define EXT3_BLOCKS_PER_GROUP(s)	((s)->s_blocks_per_group)
-# define EXT3_DESC_PER_BLOCK(s)		(EXT3_BLOCK_SIZE(s) / sizeof (struct ext3_group_desc))
+# define EXT3_DESC_PER_BLOCK(s)		(EXT3_BLOCK_SIZE(s) / EXT3_DESC_SIZE(s))
 # define EXT3_INODES_PER_GROUP(s)	((s)->s_inodes_per_group)
 #endif
 
@@ -453,7 +455,7 @@ struct ext3_super_block {
 	 * things it doesn't understand...
 	 */
 	__le32	s_first_ino;		/* First non-reserved inode */
-	__le16   s_inode_size;		/* size of inode structure */
+	__le16  s_inode_size;		/* size of inode structure */
 	__le16	s_block_group_nr;	/* block group # of this superblock */
 	__le32	s_feature_compat;	/* compatible feature set */
 /*60*/	__le32	s_feature_incompat;	/* incompatible feature set */
@@ -479,7 +481,7 @@ struct ext3_super_block {
 	__le32	s_hash_seed[4];		/* HTREE hash seed */
 	__u8	s_def_hash_version;	/* Default hash version to use */
 	__u8	s_reserved_char_pad;
-	__u16	s_reserved_word_pad;
+	__le16  s_desc_size;		/* size of group descriptor */
 	__le32	s_default_mount_opts;
 	__le32	s_first_meta_bg; 	/* First metablock block group */
 	__u32	s_reserved[190];	/* Padding to the end of the block */
@@ -562,11 +564,13 @@ static inline struct ext3_inode_info *EX
 #define EXT3_FEATURE_INCOMPAT_RECOVER		0x0004 /* Needs recovery */
 #define EXT3_FEATURE_INCOMPAT_JOURNAL_DEV	0x0008 /* Journal device */
 #define EXT3_FEATURE_INCOMPAT_META_BG		0x0010
+#define EXT3_FEATURE_INCOMPAT_DESC_SIZE		0x0020
 
 #define EXT3_FEATURE_COMPAT_SUPP	EXT2_FEATURE_COMPAT_EXT_ATTR
 #define EXT3_FEATURE_INCOMPAT_SUPP	(EXT3_FEATURE_INCOMPAT_FILETYPE| \
 					 EXT3_FEATURE_INCOMPAT_RECOVER| \
-					 EXT3_FEATURE_INCOMPAT_META_BG)
+					 EXT3_FEATURE_INCOMPAT_META_BG| \
+					 EXT3_FEATURE_INCOMPAT_DESC_SIZE)
 #define EXT3_FEATURE_RO_COMPAT_SUPP	(EXT3_FEATURE_RO_COMPAT_SPARSE_SUPER| \
 					 EXT3_FEATURE_RO_COMPAT_LARGE_FILE| \
 					 EXT3_FEATURE_RO_COMPAT_BTREE_DIR)
Index: linux-2.6.16.19/fs/ext3/balloc.c
===================================================================
--- linux-2.6.16.19.orig/fs/ext3/balloc.c	2006-06-07 13:05:52.000000000 +0200
+++ linux-2.6.16.19/fs/ext3/balloc.c	2006-06-07 13:19:31.000000000 +0200
@@ -68,10 +68,12 @@ struct ext3_group_desc * ext3_get_group_
 		return NULL;
 	}
 
-	desc = (struct ext3_group_desc *) sbi->s_group_desc[group_desc]->b_data;
+	desc = (struct ext3_group_desc *)(
+		(__u8 *)sbi->s_group_desc[group_desc]->b_data +
+		offset * EXT3_DESC_SIZE(sb));
 	if (bh)
 		*bh = sbi->s_group_desc[group_desc];
-	return desc + offset;
+	return desc;
 }
 
 /*
Index: linux-2.6.16.19/fs/ext3/inode.c
===================================================================
--- linux-2.6.16.19.orig/fs/ext3/inode.c	2006-06-07 13:05:52.000000000 +0200
+++ linux-2.6.16.19/fs/ext3/inode.c	2006-06-07 13:19:31.000000000 +0200
@@ -2285,13 +2285,14 @@ static unsigned long ext3_get_inode_bloc
 		return 0;
 	}
 
-	gdp = (struct ext3_group_desc *) bh->b_data;
+	gdp = (struct ext3_group_desc *)((__u8 *)bh->b_data + 
+	    desc * EXT3_DESC_SIZE(sb));
 	/*
 	 * Figure out the offset within the block group inode table
 	 */
 	offset = ((ino - 1) % EXT3_INODES_PER_GROUP(sb)) *
 		EXT3_INODE_SIZE(sb);
-	block = le32_to_cpu(gdp[desc].bg_inode_table) +
+	block = le32_to_cpu(gdp->bg_inode_table) +
 		(offset >> EXT3_BLOCK_SIZE_BITS(sb));
 
 	iloc->block_group = block_group;
Index: linux-2.6.16.19/fs/ext3/super.c
===================================================================
--- linux-2.6.16.19.orig/fs/ext3/super.c	2006-06-07 13:05:52.000000000 +0200
+++ linux-2.6.16.19/fs/ext3/super.c	2006-06-07 13:19:31.000000000 +0200
@@ -1172,7 +1172,8 @@ static int ext3_check_descriptors (struc
 			return 0;
 		}
 		block += EXT3_BLOCKS_PER_GROUP(sb);
-		gdp++;
+		gdp = (struct ext3_group_desc *)
+		    ((__u8 *)gdp + EXT3_DESC_SIZE(sb));
 	}
 
 	sbi->s_es->s_free_blocks_count=cpu_to_le32(ext3_count_free_blocks(sb));
@@ -1524,7 +1525,18 @@ static int ext3_fill_super (struct super
 		       sbi->s_frag_size, blocksize);
 		goto failed_mount;
 	}
-	sbi->s_frags_per_block = 1;
+	sbi->s_desc_size = le16_to_cpu(es->s_desc_size);
+	if (EXT3_HAS_INCOMPAT_FEATURE(sb, EXT3_FEATURE_INCOMPAT_DESC_SIZE)) {
+		if (sbi->s_desc_size < EXT3_MIN_DESC_SIZE ||
+		    sbi->s_desc_size > EXT3_MAX_DESC_SIZE ||
+		    sbi->s_desc_size & (sbi->s_desc_size - 1)) {
+			printk(KERN_ERR
+			       "EXT3-fs: unsupported descriptor size %d\n",
+			       sbi->s_desc_size);
+			goto failed_mount;
+		}
+	} else
+		sbi->s_desc_size = EXT3_MIN_DESC_SIZE;
 	sbi->s_blocks_per_group = le32_to_cpu(es->s_blocks_per_group);
 	sbi->s_frags_per_group = le32_to_cpu(es->s_frags_per_group);
 	sbi->s_inodes_per_group = le32_to_cpu(es->s_inodes_per_group);
@@ -1535,7 +1547,7 @@ static int ext3_fill_super (struct super
 		goto cantfind_ext3;
 	sbi->s_itb_per_group = sbi->s_inodes_per_group /
 					sbi->s_inodes_per_block;
-	sbi->s_desc_per_block = blocksize / sizeof(struct ext3_group_desc);
+	sbi->s_desc_per_block = blocksize / EXT3_DESC_SIZE(sb);
 	sbi->s_sbh = bh;
 	sbi->s_mount_state = le16_to_cpu(es->s_state);
 	sbi->s_addr_per_block_bits = log2(EXT3_ADDR_PER_BLOCK(sb));