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Subject[Ext2-devel] [PATCH] Ext2/3 forward compatibility: on-line resizing
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This patch allows forward compatibility with future filesystems which
are dynamically grown by using an alternate algorithm for storing the
block group descriptors. It's also a bit more efficient, in that it
uses just a little bit less disk space. Currently, the ext2 filesystem
format requires either relocating the inode table, or reserving space in
before doing the on-line resize. The new scheme, which is documented in
"Planned Extensions to the Ext2/3 Filesystem", by Stephen Tweedie and I (see:
http://www.usenix.org/publications/library/proceedings/usenix02/tech/freenix/tso.html)

- Ted

# This is a BitKeeper generated patch for the following project:
# Project Name: Linux kernel tree
# This patch format is intended for GNU patch command version 2.5 or higher.
# This patch includes the following deltas:
# ChangeSet 1.817 -> 1.818
# include/linux/ext2_fs.h 1.14 -> 1.15
# include/linux/ext3_fs.h 1.14 -> 1.15
# fs/ext2/super.c 1.34 -> 1.35
# fs/ext3/super.c 1.36 -> 1.37
#
# The following is the BitKeeper ChangeSet Log
# --------------------------------------------
# 02/10/18 tytso@snap.thunk.org 1.818
# Ext2/3 forward compatibility: on-line resizing
#
# This patch allows forward compatibility with future filesystems which
# are dynamically grown by using an alternate algorithm for storing
# the block group descriptors. This is also a more efficient way of
# storing the descriptors.
# --------------------------------------------
#
diff -Nru a/fs/ext2/super.c b/fs/ext2/super.c
--- a/fs/ext2/super.c Fri Oct 18 20:52:07 2002
+++ b/fs/ext2/super.c Fri Oct 18 20:52:07 2002
@@ -514,12 +514,29 @@
return res;
}

+static unsigned long descriptor_loc(struct super_block *sb,
+ unsigned long logic_sb_block,
+ int nr)
+{
+ struct ext2_sb_info *sbi = EXT2_SB(sb);
+ unsigned long bg, first_data_block, first_meta_bg;
+
+ first_data_block = le32_to_cpu(sbi->s_es->s_first_data_block);
+ first_meta_bg = le32_to_cpu(sbi->s_es->s_first_meta_bg);
+
+ if (!EXT2_HAS_INCOMPAT_FEATURE(sb, EXT2_FEATURE_INCOMPAT_META_BG) ||
+ nr < first_meta_bg)
+ return (logic_sb_block + nr + 1);
+ bg = sbi->s_desc_per_block * nr;
+ return (first_data_block + 1 + (bg * sbi->s_blocks_per_group));
+}
+
static int ext2_fill_super(struct super_block *sb, void *data, int silent)
{
struct buffer_head * bh;
struct ext2_sb_info * sbi;
struct ext2_super_block * es;
- unsigned long sb_block = 1;
+ unsigned long block, sb_block = 1;
unsigned long logic_sb_block = get_sb_block(&data);
unsigned long offset = 0;
unsigned long def_mount_opts;
@@ -735,7 +752,8 @@
goto failed_mount;
}
for (i = 0; i < db_count; i++) {
- sbi->s_group_desc[i] = sb_bread(sb, logic_sb_block + i + 1);
+ block = descriptor_loc(sb, logic_sb_block, i);
+ sbi->s_group_desc[i] = sb_bread(sb, block);
if (!sbi->s_group_desc[i]) {
for (j = 0; j < i; j++)
brelse (sbi->s_group_desc[j]);
diff -Nru a/fs/ext3/super.c b/fs/ext3/super.c
--- a/fs/ext3/super.c Fri Oct 18 20:52:07 2002
+++ b/fs/ext3/super.c Fri Oct 18 20:52:07 2002
@@ -971,6 +971,23 @@
return res;
}

+static unsigned long descriptor_loc(struct super_block *sb,
+ unsigned long logic_sb_block,
+ int nr)
+{
+ struct ext3_sb_info *sbi = EXT3_SB(sb);
+ unsigned long bg, first_data_block, first_meta_bg;
+
+ first_data_block = le32_to_cpu(sbi->s_es->s_first_data_block);
+ first_meta_bg = le32_to_cpu(sbi->s_es->s_first_meta_bg);
+
+ if (!EXT3_HAS_INCOMPAT_FEATURE(sb, EXT3_FEATURE_INCOMPAT_META_BG) ||
+ nr < first_meta_bg)
+ return (logic_sb_block + nr + 1);
+ bg = sbi->s_desc_per_block * nr;
+ return (first_data_block + 1 + (bg * sbi->s_blocks_per_group));
+}
+

static int ext3_fill_super (struct super_block *sb, void *data, int silent)
{
@@ -978,7 +995,7 @@
struct ext3_super_block *es = 0;
struct ext3_sb_info *sbi;
unsigned long sb_block = get_sb_block(&data);
- unsigned long logic_sb_block = 1;
+ unsigned long block, logic_sb_block = 1;
unsigned long offset = 0;
unsigned long journal_inum = 0;
unsigned long def_mount_opts;
@@ -1204,7 +1221,8 @@
goto failed_mount;
}
for (i = 0; i < db_count; i++) {
- sbi->s_group_desc[i] = sb_bread(sb, logic_sb_block + i + 1);
+ block = descriptor_loc(sb, logic_sb_block, i);
+ sbi->s_group_desc[i] = sb_bread(sb, block);
if (!sbi->s_group_desc[i]) {
printk (KERN_ERR "EXT3-fs: "
"can't read group descriptor %d\n", i);
diff -Nru a/include/linux/ext2_fs.h b/include/linux/ext2_fs.h
--- a/include/linux/ext2_fs.h Fri Oct 18 20:52:07 2002
+++ b/include/linux/ext2_fs.h Fri Oct 18 20:52:07 2002
@@ -399,7 +399,8 @@
__u8 s_reserved_char_pad;
__u16 s_reserved_word_pad;
__u32 s_default_mount_opts;
- __u32 s_reserved[191]; /* Padding to the end of the block */
+ __u32 s_first_meta_bg; /* First metablock block group */
+ __u32 s_reserved[190]; /* Padding to the end of the block */
};

/*
@@ -462,10 +463,12 @@
#define EXT2_FEATURE_INCOMPAT_FILETYPE 0x0002
#define EXT3_FEATURE_INCOMPAT_RECOVER 0x0004
#define EXT3_FEATURE_INCOMPAT_JOURNAL_DEV 0x0008
+#define EXT2_FEATURE_INCOMPAT_META_BG 0x0010
#define EXT2_FEATURE_INCOMPAT_ANY 0xffffffff

#define EXT2_FEATURE_COMPAT_SUPP EXT2_FEATURE_COMPAT_EXT_ATTR
-#define EXT2_FEATURE_INCOMPAT_SUPP EXT2_FEATURE_INCOMPAT_FILETYPE
+#define EXT2_FEATURE_INCOMPAT_SUPP (EXT2_FEATURE_INCOMPAT_FILETYPE| \
+ EXT2_FEATURE_INCOMPAT_META_BG)
#define EXT2_FEATURE_RO_COMPAT_SUPP (EXT2_FEATURE_RO_COMPAT_SPARSE_SUPER| \
EXT2_FEATURE_RO_COMPAT_LARGE_FILE| \
EXT2_FEATURE_RO_COMPAT_BTREE_DIR)
diff -Nru a/include/linux/ext3_fs.h b/include/linux/ext3_fs.h
--- a/include/linux/ext3_fs.h Fri Oct 18 20:52:07 2002
+++ b/include/linux/ext3_fs.h Fri Oct 18 20:52:07 2002
@@ -427,7 +427,8 @@
__u8 s_reserved_char_pad;
__u16 s_reserved_word_pad;
__u32 s_default_mount_opts;
- __u32 s_reserved[191]; /* Padding to the end of the block */
+ __u32 s_first_meta_bg; /* First metablock block group */
+ __u32 s_reserved[190]; /* Padding to the end of the block */
};

#ifdef __KERNEL__
@@ -506,10 +507,12 @@
#define EXT3_FEATURE_INCOMPAT_FILETYPE 0x0002
#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_COMPAT_SUPP EXT2_FEATURE_COMPAT_EXT_ATTR
#define EXT3_FEATURE_INCOMPAT_SUPP (EXT3_FEATURE_INCOMPAT_FILETYPE| \
- EXT3_FEATURE_INCOMPAT_RECOVER)
+ EXT3_FEATURE_INCOMPAT_RECOVER| \
+ EXT3_FEATURE_INCOMPAT_META_BG)
#define EXT3_FEATURE_RO_COMPAT_SUPP (EXT3_FEATURE_RO_COMPAT_SPARSE_SUPER| \
EXT3_FEATURE_RO_COMPAT_LARGE_FILE| \
EXT3_FEATURE_RO_COMPAT_BTREE_DIR)

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