Ext4: Uninitialized Block Groups
authorAndreas Dilger <adilger@clusterfs.com>
Tue, 16 Oct 2007 22:38:25 +0000 (18:38 -0400)
committerTheodore Ts'o <tytso@mit.edu>
Wed, 17 Oct 2007 22:50:00 +0000 (18:50 -0400)
In pass1 of e2fsck, every inode table in the fileystem is scanned and checked,
regardless of whether it is in use.  This is this the most time consuming part
of the filesystem check.  The unintialized block group feature can greatly
reduce e2fsck time by eliminating checking of uninitialized inodes.

With this feature, there is a a high water mark of used inodes for each block
group.  Block and inode bitmaps can be uninitialized on disk via a flag in the
group descriptor to avoid reading or scanning them at e2fsck time.  A checksum
of each group descriptor is used to ensure that corruption in the group
descriptor's bit flags does not cause incorrect operation.

The feature is enabled through a mkfs option

mke2fs /dev/ -O uninit_groups

A patch adding support for uninitialized block groups to e2fsprogs tools has
been posted to the linux-ext4 mailing list.

The patches have been stress tested with fsstress and fsx.  In performance
tests testing e2fsck time, we have seen that e2fsck time on ext3 grows
linearly with the total number of inodes in the filesytem.  In ext4 with the
uninitialized block groups feature, the e2fsck time is constant, based
solely on the number of used inodes rather than the total inode count.
Since typical ext4 filesystems only use 1-10% of their inodes, this feature can
greatly reduce e2fsck time for users.  With performance improvement of 2-20
times, depending on how full the filesystem is.

The attached graph shows the major improvements in e2fsck times in filesystems
with a large total inode count, but few inodes in use.

In each group descriptor if we have

EXT4_BG_INODE_UNINIT set in bg_flags:
        Inode table is not initialized/used in this group. So we can skip
        the consistency check during fsck.
EXT4_BG_BLOCK_UNINIT set in bg_flags:
        No block in the group is used. So we can skip the block bitmap
        verification for this group.

We also add two new fields to group descriptor as a part of
uninitialized group patch.

        __le16  bg_itable_unused;       /* Unused inodes count */
        __le16  bg_checksum;            /* crc16(sb_uuid+group+desc) */

bg_itable_unused:

If we have EXT4_BG_INODE_UNINIT not set in bg_flags
then bg_itable_unused will give the offset within
the inode table till the inodes are used. This can be
used by fsck to skip list of inodes that are marked unused.

bg_checksum:
Now that we depend on bg_flags and bg_itable_unused to determine
the block and inode usage, we need to make sure group descriptor
is not corrupt. We add checksum to group descriptor to
detect corruption. If the descriptor is found to be corrupt, we
mark all the blocks and inodes in the group used.

Signed-off-by: Avantika Mathur <mathur@us.ibm.com>
Signed-off-by: Andreas Dilger <adilger@clusterfs.com>
Signed-off-by: Mingming Cao <cmm@us.ibm.com>
Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
fs/Kconfig
fs/ext4/balloc.c
fs/ext4/group.h [new file with mode: 0644]
fs/ext4/ialloc.c
fs/ext4/resize.c
fs/ext4/super.c
include/linux/ext4_fs.h

index d8062745716ae407fee7948a12a88a6370e5e9aa..e31f3691b151248ee8d3e58d3c24948a61dbe637 100644 (file)
@@ -140,6 +140,7 @@ config EXT4DEV_FS
        tristate "Ext4dev/ext4 extended fs support development (EXPERIMENTAL)"
        depends on EXPERIMENTAL
        select JBD2
+       select CRC16
        help
          Ext4dev is a predecessor filesystem of the next generation
          extended fs ext4, based on ext3 filesystem code. It will be
index b74bf436844187c32cce9cc31ecdce1031a1cc1e..5927687b3e7951e6c73e804eeea828ce5c5200bd 100644 (file)
@@ -20,6 +20,7 @@
 #include <linux/quotaops.h>
 #include <linux/buffer_head.h>
 
+#include "group.h"
 /*
  * balloc.c contains the blocks allocation and deallocation routines
  */
@@ -42,6 +43,94 @@ void ext4_get_group_no_and_offset(struct super_block *sb, ext4_fsblk_t blocknr,
 
 }
 
+/* Initializes an uninitialized block bitmap if given, and returns the
+ * number of blocks free in the group. */
+unsigned ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
+                               int block_group, struct ext4_group_desc *gdp)
+{
+       unsigned long start;
+       int bit, bit_max;
+       unsigned free_blocks, group_blocks;
+       struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+       if (bh) {
+               J_ASSERT_BH(bh, buffer_locked(bh));
+
+               /* If checksum is bad mark all blocks used to prevent allocation
+                * essentially implementing a per-group read-only flag. */
+               if (!ext4_group_desc_csum_verify(sbi, block_group, gdp)) {
+                       ext4_error(sb, __FUNCTION__,
+                                  "Checksum bad for group %u\n", block_group);
+                       gdp->bg_free_blocks_count = 0;
+                       gdp->bg_free_inodes_count = 0;
+                       gdp->bg_itable_unused = 0;
+                       memset(bh->b_data, 0xff, sb->s_blocksize);
+                       return 0;
+               }
+               memset(bh->b_data, 0, sb->s_blocksize);
+       }
+
+       /* Check for superblock and gdt backups in this group */
+       bit_max = ext4_bg_has_super(sb, block_group);
+
+       if (!EXT4_HAS_INCOMPAT_FEATURE(sb, EXT4_FEATURE_INCOMPAT_META_BG) ||
+           block_group < le32_to_cpu(sbi->s_es->s_first_meta_bg) *
+                         sbi->s_desc_per_block) {
+               if (bit_max) {
+                       bit_max += ext4_bg_num_gdb(sb, block_group);
+                       bit_max +=
+                               le16_to_cpu(sbi->s_es->s_reserved_gdt_blocks);
+               }
+       } else { /* For META_BG_BLOCK_GROUPS */
+               int group_rel = (block_group -
+                                le32_to_cpu(sbi->s_es->s_first_meta_bg)) %
+                               EXT4_DESC_PER_BLOCK(sb);
+               if (group_rel == 0 || group_rel == 1 ||
+                   (group_rel == EXT4_DESC_PER_BLOCK(sb) - 1))
+                       bit_max += 1;
+       }
+
+       if (block_group == sbi->s_groups_count - 1) {
+               /*
+                * Even though mke2fs always initialize first and last group
+                * if some other tool enabled the EXT4_BG_BLOCK_UNINIT we need
+                * to make sure we calculate the right free blocks
+                */
+               group_blocks = ext4_blocks_count(sbi->s_es) -
+                       le32_to_cpu(sbi->s_es->s_first_data_block) -
+                       (EXT4_BLOCKS_PER_GROUP(sb) * (sbi->s_groups_count -1));
+       } else {
+               group_blocks = EXT4_BLOCKS_PER_GROUP(sb);
+       }
+
+       free_blocks = group_blocks - bit_max;
+
+       if (bh) {
+               for (bit = 0; bit < bit_max; bit++)
+                       ext4_set_bit(bit, bh->b_data);
+
+               start = block_group * EXT4_BLOCKS_PER_GROUP(sb) +
+                       le32_to_cpu(sbi->s_es->s_first_data_block);
+
+               /* Set bits for block and inode bitmaps, and inode table */
+               ext4_set_bit(ext4_block_bitmap(sb, gdp) - start, bh->b_data);
+               ext4_set_bit(ext4_inode_bitmap(sb, gdp) - start, bh->b_data);
+               for (bit = le32_to_cpu(gdp->bg_inode_table) - start,
+                    bit_max = bit + sbi->s_itb_per_group; bit < bit_max; bit++)
+                       ext4_set_bit(bit, bh->b_data);
+
+               /*
+                * Also if the number of blocks within the group is
+                * less than the blocksize * 8 ( which is the size
+                * of bitmap ), set rest of the block bitmap to 1
+                */
+               mark_bitmap_end(group_blocks, sb->s_blocksize * 8, bh->b_data);
+       }
+
+       return free_blocks - sbi->s_itb_per_group - 2;
+}
+
+
 /*
  * The free blocks are managed by bitmaps.  A file system contains several
  * blocks groups.  Each group contains 1 bitmap block for blocks, 1 bitmap
@@ -119,7 +208,7 @@ block_in_use(ext4_fsblk_t block, struct super_block *sb, unsigned char *map)
  *
  * Return buffer_head on success or NULL in case of failure.
  */
-static struct buffer_head *
+struct buffer_head *
 read_block_bitmap(struct super_block *sb, unsigned int block_group)
 {
        int i;
@@ -127,11 +216,24 @@ read_block_bitmap(struct super_block *sb, unsigned int block_group)
        struct buffer_head * bh = NULL;
        ext4_fsblk_t bitmap_blk;
 
-       desc = ext4_get_group_desc (sb, block_group, NULL);
+       desc = ext4_get_group_desc(sb, block_group, NULL);
        if (!desc)
                return NULL;
        bitmap_blk = ext4_block_bitmap(sb, desc);
-       bh = sb_bread(sb, bitmap_blk);
+       if (desc->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
+               bh = sb_getblk(sb, bitmap_blk);
+               if (!buffer_uptodate(bh)) {
+                       lock_buffer(bh);
+                       if (!buffer_uptodate(bh)) {
+                               ext4_init_block_bitmap(sb, bh, block_group,
+                                                      desc);
+                               set_buffer_uptodate(bh);
+                       }
+                       unlock_buffer(bh);
+               }
+       } else {
+               bh = sb_bread(sb, bitmap_blk);
+       }
        if (!bh)
                ext4_error (sb, __FUNCTION__,
                            "Cannot read block bitmap - "
@@ -627,6 +729,7 @@ do_more:
        desc->bg_free_blocks_count =
                cpu_to_le16(le16_to_cpu(desc->bg_free_blocks_count) +
                        group_freed);
+       desc->bg_checksum = ext4_group_desc_csum(sbi, block_group, desc);
        spin_unlock(sb_bgl_lock(sbi, block_group));
        percpu_counter_add(&sbi->s_freeblocks_counter, count);
 
@@ -1685,8 +1788,11 @@ allocated:
                        ret_block, goal_hits, goal_attempts);
 
        spin_lock(sb_bgl_lock(sbi, group_no));
+       if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT))
+               gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
        gdp->bg_free_blocks_count =
                        cpu_to_le16(le16_to_cpu(gdp->bg_free_blocks_count)-num);
+       gdp->bg_checksum = ext4_group_desc_csum(sbi, group_no, gdp);
        spin_unlock(sb_bgl_lock(sbi, group_no));
        percpu_counter_sub(&sbi->s_freeblocks_counter, num);
 
diff --git a/fs/ext4/group.h b/fs/ext4/group.h
new file mode 100644 (file)
index 0000000..1577910
--- /dev/null
@@ -0,0 +1,27 @@
+/*
+ *  linux/fs/ext4/group.h
+ *
+ * Copyright (C) 2007 Cluster File Systems, Inc
+ *
+ * Author: Andreas Dilger <adilger@clusterfs.com>
+ */
+
+#ifndef _LINUX_EXT4_GROUP_H
+#define _LINUX_EXT4_GROUP_H
+
+extern __le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 group,
+                                  struct ext4_group_desc *gdp);
+extern int ext4_group_desc_csum_verify(struct ext4_sb_info *sbi, __u32 group,
+                                      struct ext4_group_desc *gdp);
+struct buffer_head *read_block_bitmap(struct super_block *sb,
+                                     unsigned int block_group);
+extern unsigned ext4_init_block_bitmap(struct super_block *sb,
+                                      struct buffer_head *bh, int group,
+                                      struct ext4_group_desc *desc);
+#define ext4_free_blocks_after_init(sb, group, desc)                   \
+               ext4_init_block_bitmap(sb, NULL, group, desc)
+extern unsigned ext4_init_inode_bitmap(struct super_block *sb,
+                                      struct buffer_head *bh, int group,
+                                      struct ext4_group_desc *desc);
+extern void mark_bitmap_end(int start_bit, int end_bit, char *bitmap);
+#endif /* _LINUX_EXT4_GROUP_H */
index 38e9a0a705dffacb0ba42548e327c7dd706c8d09..c61f37fd3f05e4d72061791d79600024c858df97 100644 (file)
@@ -28,6 +28,7 @@
 
 #include "xattr.h"
 #include "acl.h"
+#include "group.h"
 
 /*
  * ialloc.c contains the inodes allocation and deallocation routines
  * the free blocks count in the block.
  */
 
+/*
+ * To avoid calling the atomic setbit hundreds or thousands of times, we only
+ * need to use it within a single byte (to ensure we get endianness right).
+ * We can use memset for the rest of the bitmap as there are no other users.
+ */
+void mark_bitmap_end(int start_bit, int end_bit, char *bitmap)
+{
+       int i;
+
+       if (start_bit >= end_bit)
+               return;
+
+       ext4_debug("mark end bits +%d through +%d used\n", start_bit, end_bit);
+       for (i = start_bit; i < ((start_bit + 7) & ~7UL); i++)
+               ext4_set_bit(i, bitmap);
+       if (i < end_bit)
+               memset(bitmap + (i >> 3), 0xff, (end_bit - i) >> 3);
+}
+
+/* Initializes an uninitialized inode bitmap */
+unsigned ext4_init_inode_bitmap(struct super_block *sb,
+                               struct buffer_head *bh, int block_group,
+                               struct ext4_group_desc *gdp)
+{
+       struct ext4_sb_info *sbi = EXT4_SB(sb);
+
+       J_ASSERT_BH(bh, buffer_locked(bh));
+
+       /* If checksum is bad mark all blocks and inodes use to prevent
+        * allocation, essentially implementing a per-group read-only flag. */
+       if (!ext4_group_desc_csum_verify(sbi, block_group, gdp)) {
+               ext4_error(sb, __FUNCTION__, "Checksum bad for group %u\n",
+                          block_group);
+               gdp->bg_free_blocks_count = 0;
+               gdp->bg_free_inodes_count = 0;
+               gdp->bg_itable_unused = 0;
+               memset(bh->b_data, 0xff, sb->s_blocksize);
+               return 0;
+       }
+
+       memset(bh->b_data, 0, (EXT4_INODES_PER_GROUP(sb) + 7) / 8);
+       mark_bitmap_end(EXT4_INODES_PER_GROUP(sb), EXT4_BLOCKS_PER_GROUP(sb),
+                       bh->b_data);
+
+       return EXT4_INODES_PER_GROUP(sb);
+}
 
 /*
  * Read the inode allocation bitmap for a given block_group, reading
@@ -59,8 +106,20 @@ read_inode_bitmap(struct super_block * sb, unsigned long block_group)
        desc = ext4_get_group_desc(sb, block_group, NULL);
        if (!desc)
                goto error_out;
-
-       bh = sb_bread(sb, ext4_inode_bitmap(sb, desc));
+       if (desc->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
+               bh = sb_getblk(sb, ext4_inode_bitmap(sb, desc));
+               if (!buffer_uptodate(bh)) {
+                       lock_buffer(bh);
+                       if (!buffer_uptodate(bh)) {
+                               ext4_init_inode_bitmap(sb, bh, block_group,
+                                                      desc);
+                               set_buffer_uptodate(bh);
+                       }
+                       unlock_buffer(bh);
+               }
+       } else {
+               bh = sb_bread(sb, ext4_inode_bitmap(sb, desc));
+       }
        if (!bh)
                ext4_error(sb, "read_inode_bitmap",
                            "Cannot read inode bitmap - "
@@ -169,6 +228,8 @@ void ext4_free_inode (handle_t *handle, struct inode * inode)
                        if (is_directory)
                                gdp->bg_used_dirs_count = cpu_to_le16(
                                  le16_to_cpu(gdp->bg_used_dirs_count) - 1);
+                       gdp->bg_checksum = ext4_group_desc_csum(sbi,
+                                                       block_group, gdp);
                        spin_unlock(sb_bgl_lock(sbi, block_group));
                        percpu_counter_inc(&sbi->s_freeinodes_counter);
                        if (is_directory)
@@ -435,7 +496,7 @@ struct inode *ext4_new_inode(handle_t *handle, struct inode * dir, int mode)
        struct ext4_sb_info *sbi;
        int err = 0;
        struct inode *ret;
-       int i;
+       int i, free = 0;
 
        /* Cannot create files in a deleted directory */
        if (!dir || !dir->i_nlink)
@@ -517,11 +578,13 @@ repeat_in_this_group:
        goto out;
 
 got:
-       ino += group * EXT4_INODES_PER_GROUP(sb) + 1;
-       if (ino < EXT4_FIRST_INO(sb) || ino > le32_to_cpu(es->s_inodes_count)) {
-               ext4_error (sb, "ext4_new_inode",
-                           "reserved inode or inode > inodes count - "
-                           "block_group = %d, inode=%lu", group, ino);
+       ino++;
+       if ((group == 0 && ino < EXT4_FIRST_INO(sb)) ||
+           ino > EXT4_INODES_PER_GROUP(sb)) {
+               ext4_error(sb, __FUNCTION__,
+                          "reserved inode or inode > inodes count - "
+                          "block_group = %d, inode=%lu", group,
+                          ino + group * EXT4_INODES_PER_GROUP(sb));
                err = -EIO;
                goto fail;
        }
@@ -529,13 +592,78 @@ got:
        BUFFER_TRACE(bh2, "get_write_access");
        err = ext4_journal_get_write_access(handle, bh2);
        if (err) goto fail;
+
+       /* We may have to initialize the block bitmap if it isn't already */
+       if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM) &&
+           gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
+               struct buffer_head *block_bh = read_block_bitmap(sb, group);
+
+               BUFFER_TRACE(block_bh, "get block bitmap access");
+               err = ext4_journal_get_write_access(handle, block_bh);
+               if (err) {
+                       brelse(block_bh);
+                       goto fail;
+               }
+
+               free = 0;
+               spin_lock(sb_bgl_lock(sbi, group));
+               /* recheck and clear flag under lock if we still need to */
+               if (gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
+                       gdp->bg_flags &= cpu_to_le16(~EXT4_BG_BLOCK_UNINIT);
+                       free = ext4_free_blocks_after_init(sb, group, gdp);
+                       gdp->bg_free_blocks_count = cpu_to_le16(free);
+               }
+               spin_unlock(sb_bgl_lock(sbi, group));
+
+               /* Don't need to dirty bitmap block if we didn't change it */
+               if (free) {
+                       BUFFER_TRACE(block_bh, "dirty block bitmap");
+                       err = ext4_journal_dirty_metadata(handle, block_bh);
+               }
+
+               brelse(block_bh);
+               if (err)
+                       goto fail;
+       }
+
        spin_lock(sb_bgl_lock(sbi, group));
+       /* If we didn't allocate from within the initialized part of the inode
+        * table then we need to initialize up to this inode. */
+       if (EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
+               if (gdp->bg_flags & cpu_to_le16(EXT4_BG_INODE_UNINIT)) {
+                       gdp->bg_flags &= cpu_to_le16(~EXT4_BG_INODE_UNINIT);
+
+                       /* When marking the block group with
+                        * ~EXT4_BG_INODE_UNINIT we don't want to depend
+                        * on the value of bg_itable_unsed even though
+                        * mke2fs could have initialized the same for us.
+                        * Instead we calculated the value below
+                        */
+
+                       free = 0;
+               } else {
+                       free = EXT4_INODES_PER_GROUP(sb) -
+                               le16_to_cpu(gdp->bg_itable_unused);
+               }
+
+               /*
+                * Check the relative inode number against the last used
+                * relative inode number in this group. if it is greater
+                * we need to  update the bg_itable_unused count
+                *
+                */
+               if (ino > free)
+                       gdp->bg_itable_unused =
+                               cpu_to_le16(EXT4_INODES_PER_GROUP(sb) - ino);
+       }
+
        gdp->bg_free_inodes_count =
                cpu_to_le16(le16_to_cpu(gdp->bg_free_inodes_count) - 1);
        if (S_ISDIR(mode)) {
                gdp->bg_used_dirs_count =
                        cpu_to_le16(le16_to_cpu(gdp->bg_used_dirs_count) + 1);
        }
+       gdp->bg_checksum = ext4_group_desc_csum(sbi, group, gdp);
        spin_unlock(sb_bgl_lock(sbi, group));
        BUFFER_TRACE(bh2, "call ext4_journal_dirty_metadata");
        err = ext4_journal_dirty_metadata(handle, bh2);
@@ -557,7 +685,7 @@ got:
                inode->i_gid = current->fsgid;
        inode->i_mode = mode;
 
-       inode->i_ino = ino;
+       inode->i_ino = ino + group * EXT4_INODES_PER_GROUP(sb);
        /* This is the optimal IO size (for stat), not the fs block size */
        inode->i_blocks = 0;
        inode->i_mtime = inode->i_atime = inode->i_ctime = ei->i_crtime =
index 472fc0d3e1c0776de5e4594321e66b69795bd1ed..0a7e914c495a861625cd01834544531b15e2748b 100644 (file)
@@ -16,6 +16,7 @@
 #include <linux/errno.h>
 #include <linux/slab.h>
 
+#include "group.h"
 
 #define outside(b, first, last)        ((b) < (first) || (b) >= (last))
 #define inside(b, first, last) ((b) >= (first) && (b) < (last))
@@ -139,25 +140,6 @@ static struct buffer_head *bclean(handle_t *handle, struct super_block *sb,
        return bh;
 }
 
-/*
- * To avoid calling the atomic setbit hundreds or thousands of times, we only
- * need to use it within a single byte (to ensure we get endianness right).
- * We can use memset for the rest of the bitmap as there are no other users.
- */
-static void mark_bitmap_end(int start_bit, int end_bit, char *bitmap)
-{
-       int i;
-
-       if (start_bit >= end_bit)
-               return;
-
-       ext4_debug("mark end bits +%d through +%d used\n", start_bit, end_bit);
-       for (i = start_bit; i < ((start_bit + 7) & ~7UL); i++)
-               ext4_set_bit(i, bitmap);
-       if (i < end_bit)
-               memset(bitmap + (i >> 3), 0xff, (end_bit - i) >> 3);
-}
-
 /*
  * Set up the block and inode bitmaps, and the inode table for the new group.
  * This doesn't need to be part of the main transaction, since we are only
@@ -842,6 +824,7 @@ int ext4_group_add(struct super_block *sb, struct ext4_new_group_data *input)
        ext4_inode_table_set(sb, gdp, input->inode_table); /* LV FIXME */
        gdp->bg_free_blocks_count = cpu_to_le16(input->free_blocks_count);
        gdp->bg_free_inodes_count = cpu_to_le16(EXT4_INODES_PER_GROUP(sb));
+       gdp->bg_checksum = ext4_group_desc_csum(sbi, input->group, gdp);
 
        /*
         * Make the new blocks and inodes valid next.  We do this before
index e2bdf93693a6e5f370dcd4dfaf977e7278cda5d7..dd4ff9c87358227b0b219ad29977896345b9c323 100644 (file)
 #include <linux/quotaops.h>
 #include <linux/seq_file.h>
 #include <linux/log2.h>
+#include <linux/crc16.h>
 
 #include <asm/uaccess.h>
 
 #include "xattr.h"
 #include "acl.h"
 #include "namei.h"
+#include "group.h"
 
 static int ext4_load_journal(struct super_block *, struct ext4_super_block *,
                             unsigned long journal_devnum);
@@ -1308,6 +1310,43 @@ static int ext4_setup_super(struct super_block *sb, struct ext4_super_block *es,
        return res;
 }
 
+__le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 block_group,
+                           struct ext4_group_desc *gdp)
+{
+       __u16 crc = 0;
+
+       if (sbi->s_es->s_feature_ro_compat &
+           cpu_to_le32(EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) {
+               int offset = offsetof(struct ext4_group_desc, bg_checksum);
+               __le32 le_group = cpu_to_le32(block_group);
+
+               crc = crc16(~0, sbi->s_es->s_uuid, sizeof(sbi->s_es->s_uuid));
+               crc = crc16(crc, (__u8 *)&le_group, sizeof(le_group));
+               crc = crc16(crc, (__u8 *)gdp, offset);
+               offset += sizeof(gdp->bg_checksum); /* skip checksum */
+               /* for checksum of struct ext4_group_desc do the rest...*/
+               if ((sbi->s_es->s_feature_incompat &
+                    cpu_to_le32(EXT4_FEATURE_INCOMPAT_64BIT)) &&
+                   offset < le16_to_cpu(sbi->s_es->s_desc_size))
+                       crc = crc16(crc, (__u8 *)gdp + offset,
+                                   le16_to_cpu(sbi->s_es->s_desc_size) -
+                                       offset);
+       }
+
+       return cpu_to_le16(crc);
+}
+
+int ext4_group_desc_csum_verify(struct ext4_sb_info *sbi, __u32 block_group,
+                               struct ext4_group_desc *gdp)
+{
+       if ((sbi->s_es->s_feature_ro_compat &
+            cpu_to_le32(EXT4_FEATURE_RO_COMPAT_GDT_CSUM)) &&
+           (gdp->bg_checksum != ext4_group_desc_csum(sbi, block_group, gdp)))
+               return 0;
+
+       return 1;
+}
+
 /* Called at mount-time, super-block is locked */
 static int ext4_check_descriptors (struct super_block * sb)
 {
@@ -1362,6 +1401,14 @@ static int ext4_check_descriptors (struct super_block * sb)
                                    i, inode_table);
                        return 0;
                }
+               if (!ext4_group_desc_csum_verify(sbi, i, gdp)) {
+                       ext4_error(sb, __FUNCTION__,
+                                  "Checksum for group %d failed (%u!=%u)\n", i,
+                                  le16_to_cpu(ext4_group_desc_csum(sbi, i,
+                                                                   gdp)),
+                                  le16_to_cpu(gdp->bg_checksum));
+                       return 0;
+               }
                first_block += EXT4_BLOCKS_PER_GROUP(sb);
                gdp = (struct ext4_group_desc *)
                        ((__u8 *)gdp + EXT4_DESC_SIZE(sb));
index 151738af6be2b970af0b90b23cbd4f57ccccd3bb..b77b59fe7f5686262068eb85a7f16e0e44697aeb 100644 (file)
  */
 struct ext4_group_desc
 {
-       __le32  bg_block_bitmap;                /* Blocks bitmap block */
-       __le32  bg_inode_bitmap;                /* Inodes bitmap block */
+       __le32  bg_block_bitmap;        /* Blocks bitmap block */
+       __le32  bg_inode_bitmap;        /* Inodes bitmap block */
        __le32  bg_inode_table;         /* Inodes table block */
        __le16  bg_free_blocks_count;   /* Free blocks count */
        __le16  bg_free_inodes_count;   /* Free inodes count */
        __le16  bg_used_dirs_count;     /* Directories count */
-       __u16   bg_flags;
-       __u32   bg_reserved[3];
+       __le16  bg_flags;               /* EXT4_BG_flags (INODE_UNINIT, etc) */
+       __u32   bg_reserved[2];         /* Likely block/inode bitmap checksum */
+       __le16  bg_itable_unused;       /* Unused inodes count */
+       __le16  bg_checksum;            /* crc16(sb_uuid+group+desc) */
        __le32  bg_block_bitmap_hi;     /* Blocks bitmap block MSB */
        __le32  bg_inode_bitmap_hi;     /* Inodes bitmap block MSB */
        __le32  bg_inode_table_hi;      /* Inodes table block MSB */
 };
 
+#define EXT4_BG_INODE_UNINIT   0x0001 /* Inode table/bitmap not in use */
+#define EXT4_BG_BLOCK_UNINIT   0x0002 /* Block bitmap not in use */
+#define EXT4_BG_INODE_ZEROED   0x0004 /* On-disk itable initialized to zero */
+
 #ifdef __KERNEL__
 #include <linux/ext4_fs_i.h>
 #include <linux/ext4_fs_sb.h>
@@ -665,6 +671,7 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
 #define EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER    0x0001
 #define EXT4_FEATURE_RO_COMPAT_LARGE_FILE      0x0002
 #define EXT4_FEATURE_RO_COMPAT_BTREE_DIR       0x0004
+#define EXT4_FEATURE_RO_COMPAT_GDT_CSUM                0x0010
 #define EXT4_FEATURE_RO_COMPAT_DIR_NLINK       0x0020
 #define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE     0x0040
 
@@ -684,6 +691,7 @@ static inline int ext4_valid_inum(struct super_block *sb, unsigned long ino)
                                         EXT4_FEATURE_INCOMPAT_64BIT)
 #define EXT4_FEATURE_RO_COMPAT_SUPP    (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
                                         EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
+                                        EXT4_FEATURE_RO_COMPAT_GDT_CSUM| \
                                         EXT4_FEATURE_RO_COMPAT_DIR_NLINK | \
                                         EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE | \
                                         EXT4_FEATURE_RO_COMPAT_BTREE_DIR)