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Subject[RFC] ext4: Rework metadata_csum/gdt_csum flag handling in kernel
Ok, I've reworked the block group descriptor checksum handling code per this
email thread. INCOMPAT_BG_USE_META_CSUM is gone. METADATA_CSUM implies (and
in fact overrides) GDT_CSUM, though the group descriptor checksum uses the same
function as all other metadata blocks' checksums (by default crc32c). I
created a helper function to determine if group descriptor checksums are
enabled, and the actual gdt checksum verify/set functions are smart enough to
use the correct function.

Below are the changes that I intend to make to the kernel. I'll integrate these
changes into the (huge) kernel patchset, but wanted to aggregate the changes
here first to avoid overwhelming reviewers.

Question: What will happen to old kernels when METADATA_CSUM and GDT_CSUM are
set? Should the kernel reject the combination and ask for fsck? I think it
will be ok, but older kernels might not be...?

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
---
fs/ext4/balloc.c | 4 ++--
fs/ext4/ext4.h | 20 +++++++++++++++-----
fs/ext4/ialloc.c | 19 ++++++++-----------
fs/ext4/inode.c | 3 +--
fs/ext4/mballoc.c | 6 +++---
fs/ext4/resize.c | 9 +++------
fs/ext4/super.c | 23 ++++++++++-------------
7 files changed, 42 insertions(+), 42 deletions(-)
diff --git a/fs/ext4/balloc.c b/fs/ext4/balloc.c
index 6eee0e6..b5a7951 100644
--- a/fs/ext4/balloc.c
+++ b/fs/ext4/balloc.c
@@ -168,7 +168,7 @@ void ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *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)) {
+ if (!ext4_group_desc_csum_verify(sb, block_group, gdp)) {
ext4_error(sb, "Checksum bad for group %u", block_group);
ext4_free_group_clusters_set(sb, gdp, 0);
ext4_free_inodes_set(sb, gdp, 0);
@@ -214,7 +214,7 @@ void ext4_init_block_bitmap(struct super_block *sb, struct buffer_head *bh,
sb->s_blocksize * 8, bh->b_data);
ext4_block_bitmap_csum_set(sb, block_group, gdp, bh,
EXT4_BLOCKS_PER_GROUP(sb) / 8);
- ext4_group_desc_csum_set(sbi, block_group, gdp);
+ ext4_group_desc_csum_set(sb, block_group, gdp);
}

/* Return the number of free blocks in a block group. It is used when
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 70bd236..a518930 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1434,6 +1434,11 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
#define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE 0x0040
#define EXT4_FEATURE_RO_COMPAT_QUOTA 0x0100
#define EXT4_FEATURE_RO_COMPAT_BIGALLOC 0x0200
+/*
+ * METADATA_CSUM implies GDT_CSUM. When METADATA_CSUM is set, group
+ * descriptor checksums use the same algorithm as all other data
+ * structures' checksums.
+ */
#define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM 0x0400

#define EXT4_FEATURE_INCOMPAT_COMPRESSION 0x0001
@@ -1449,7 +1454,6 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
#define EXT4_FEATURE_INCOMPAT_DIRDATA 0x1000 /* data in dirent */
#define EXT4_FEATURE_INCOMPAT_INLINEDATA 0x2000 /* data in inode */
#define EXT4_FEATURE_INCOMPAT_LARGEDIR 0x4000 /* >2GB or 3-lvl htree */
-#define EXT4_FEATURE_INCOMPAT_BG_USE_META_CSUM 0x8000

#define EXT2_FEATURE_COMPAT_SUPP EXT4_FEATURE_COMPAT_EXT_ATTR
#define EXT2_FEATURE_INCOMPAT_SUPP (EXT4_FEATURE_INCOMPAT_FILETYPE| \
@@ -1473,8 +1477,7 @@ static inline void ext4_clear_state_flags(struct ext4_inode_info *ei)
EXT4_FEATURE_INCOMPAT_EXTENTS| \
EXT4_FEATURE_INCOMPAT_64BIT| \
EXT4_FEATURE_INCOMPAT_FLEX_BG| \
- EXT4_FEATURE_INCOMPAT_MMP| \
- EXT4_FEATURE_INCOMPAT_BG_USE_META_CSUM)
+ EXT4_FEATURE_INCOMPAT_MMP)
#define EXT4_FEATURE_RO_COMPAT_SUPP (EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER| \
EXT4_FEATURE_RO_COMPAT_LARGE_FILE| \
EXT4_FEATURE_RO_COMPAT_GDT_CSUM| \
@@ -2092,11 +2095,18 @@ extern void ext4_used_dirs_set(struct super_block *sb,
struct ext4_group_desc *bg, __u32 count);
extern void ext4_itable_unused_set(struct super_block *sb,
struct ext4_group_desc *bg, __u32 count);
-extern int ext4_group_desc_csum_verify(struct ext4_sb_info *sbi, __u32 group,
+extern int ext4_group_desc_csum_verify(struct super_block *sb, __u32 group,
struct ext4_group_desc *gdp);
-extern void ext4_group_desc_csum_set(struct ext4_sb_info *sbi, __u32 group,
+extern void ext4_group_desc_csum_set(struct super_block *sb, __u32 group,
struct ext4_group_desc *gdp);

+static inline int ext4_has_group_desc_csum(struct super_block *sb)
+{
+ return EXT4_HAS_RO_COMPAT_FEATURE(sb,
+ EXT4_FEATURE_RO_COMPAT_GDT_CSUM |
+ EXT4_FEATURE_RO_COMPAT_METADATA_CSUM);
+}
+
static inline ext4_fsblk_t ext4_blocks_count(struct ext4_super_block *es)
{
return ((ext4_fsblk_t)le32_to_cpu(es->s_blocks_count_hi) << 32) |
diff --git a/fs/ext4/ialloc.c b/fs/ext4/ialloc.c
index b9b6b27..1ade34d 100644
--- a/fs/ext4/ialloc.c
+++ b/fs/ext4/ialloc.c
@@ -70,13 +70,11 @@ static unsigned ext4_init_inode_bitmap(struct super_block *sb,
ext4_group_t 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)) {
+ if (!ext4_group_desc_csum_verify(sb, block_group, gdp)) {
ext4_error(sb, "Checksum bad for group %u", block_group);
ext4_free_group_clusters_set(sb, gdp, 0);
ext4_free_inodes_set(sb, gdp, 0);
@@ -92,7 +90,7 @@ static unsigned ext4_init_inode_bitmap(struct super_block *sb,
bh->b_data);
ext4_inode_bitmap_csum_set(sb, block_group, gdp, bh,
EXT4_INODES_PER_GROUP(sb) / 8);
- ext4_group_desc_csum_set(sbi, block_group, gdp);
+ ext4_group_desc_csum_set(sb, block_group, gdp);

return EXT4_INODES_PER_GROUP(sb);
}
@@ -287,7 +285,7 @@ void ext4_free_inode(handle_t *handle, struct inode *inode)
}
ext4_inode_bitmap_csum_set(sb, block_group, gdp, bitmap_bh,
EXT4_INODES_PER_GROUP(sb) / 8);
- ext4_group_desc_csum_set(sbi, block_group, gdp);
+ ext4_group_desc_csum_set(sb, block_group, gdp);
ext4_unlock_group(sb, block_group);

percpu_counter_inc(&sbi->s_freeinodes_counter);
@@ -657,8 +655,7 @@ static int ext4_claim_inode(struct super_block *sb,
}
/* 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 (ext4_has_group_desc_csum(sb)) {
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
@@ -697,7 +694,7 @@ static int ext4_claim_inode(struct super_block *sb,
}
ext4_inode_bitmap_csum_set(sb, group, gdp, inode_bitmap_bh,
EXT4_INODES_PER_GROUP(sb) / 8);
- ext4_group_desc_csum_set(sbi, group, gdp);
+ ext4_group_desc_csum_set(sb, group, gdp);
err_ret:
ext4_unlock_group(sb, group);
up_read(&grp->alloc_sem);
@@ -832,7 +829,7 @@ repeat_in_this_group:

got:
/* 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) &&
+ if (ext4_has_group_desc_csum(sb) &&
gdp->bg_flags & cpu_to_le16(EXT4_BG_BLOCK_UNINIT)) {
struct buffer_head *block_bitmap_bh;

@@ -858,7 +855,7 @@ got:
block_bitmap_bh,
EXT4_BLOCKS_PER_GROUP(sb) /
8);
- ext4_group_desc_csum_set(sbi, group, gdp);
+ ext4_group_desc_csum_set(sb, group, gdp);
}
ext4_unlock_group(sb, group);

@@ -1226,7 +1223,7 @@ int ext4_init_inode_table(struct super_block *sb, ext4_group_t group,
skip_zeroout:
ext4_lock_group(sb, group);
gdp->bg_flags |= cpu_to_le16(EXT4_BG_INODE_ZEROED);
- ext4_group_desc_csum_set(sbi, group, gdp);
+ ext4_group_desc_csum_set(sb, group, gdp);
ext4_unlock_group(sb, group);

BUFFER_TRACE(group_desc_bh,
diff --git a/fs/ext4/inode.c b/fs/ext4/inode.c
index c0200cf..e94ac91 100644
--- a/fs/ext4/inode.c
+++ b/fs/ext4/inode.c
@@ -3573,8 +3573,7 @@ make_io:
b = table;
end = b + EXT4_SB(sb)->s_inode_readahead_blks;
num = EXT4_INODES_PER_GROUP(sb);
- if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
- EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
+ if (ext4_has_group_desc_csum(sb))
num -= ext4_itable_unused_count(sb, gdp);
table += num / inodes_per_block;
if (end > table)
diff --git a/fs/ext4/mballoc.c b/fs/ext4/mballoc.c
index 5f2e2ed..d6062e7 100644
--- a/fs/ext4/mballoc.c
+++ b/fs/ext4/mballoc.c
@@ -2919,7 +2919,7 @@ ext4_mb_mark_diskspace_used(struct ext4_allocation_context *ac,
ext4_free_group_clusters_set(sb, gdp, len);
ext4_block_bitmap_csum_set(sb, ac->ac_b_ex.fe_group, gdp, bitmap_bh,
EXT4_BLOCKS_PER_GROUP(sb) / 8);
- ext4_group_desc_csum_set(sbi, ac->ac_b_ex.fe_group, gdp);
+ ext4_group_desc_csum_set(sb, ac->ac_b_ex.fe_group, gdp);

ext4_unlock_group(sb, ac->ac_b_ex.fe_group);
percpu_counter_sub(&sbi->s_freeclusters_counter, ac->ac_b_ex.fe_len);
@@ -4787,7 +4787,7 @@ do_more:
ext4_free_group_clusters_set(sb, gdp, ret);
ext4_block_bitmap_csum_set(sb, block_group, gdp, bitmap_bh,
EXT4_BLOCKS_PER_GROUP(sb) / 8);
- ext4_group_desc_csum_set(sbi, block_group, gdp);
+ ext4_group_desc_csum_set(sb, block_group, gdp);
ext4_unlock_group(sb, block_group);
percpu_counter_add(&sbi->s_freeclusters_counter, count_clusters);

@@ -4933,7 +4933,7 @@ int ext4_group_add_blocks(handle_t *handle, struct super_block *sb,
ext4_free_group_clusters_set(sb, desc, blk_free_count);
ext4_block_bitmap_csum_set(sb, block_group, desc, bitmap_bh,
EXT4_BLOCKS_PER_GROUP(sb) / 8);
- ext4_group_desc_csum_set(sbi, block_group, desc);
+ ext4_group_desc_csum_set(sb, block_group, desc);
ext4_unlock_group(sb, block_group);
percpu_counter_add(&sbi->s_freeclusters_counter,
EXT4_B2C(sbi, blocks_freed));
diff --git a/fs/ext4/resize.c b/fs/ext4/resize.c
index 2363532..21ace95 100644
--- a/fs/ext4/resize.c
+++ b/fs/ext4/resize.c
@@ -1106,7 +1106,7 @@ static int ext4_setup_new_descs(handle_t *handle, struct super_block *sb,
EXT4_B2C(sbi, group_data->free_blocks_count));
ext4_free_inodes_set(sb, gdp, EXT4_INODES_PER_GROUP(sb));
gdp->bg_flags = cpu_to_le16(*bg_flags);
- ext4_group_desc_csum_set(sbi, group, gdp);
+ ext4_group_desc_csum_set(sb, group, gdp);

err = ext4_handle_dirty_metadata(handle, NULL, gdb_bh);
if (unlikely(err)) {
@@ -1342,17 +1342,14 @@ static int ext4_setup_next_flex_gd(struct super_block *sb,
(1 + ext4_bg_num_gdb(sb, group + i) +
le16_to_cpu(es->s_reserved_gdt_blocks)) : 0;
group_data[i].free_blocks_count = blocks_per_group - overhead;
- if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
- EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
+ if (ext4_has_group_desc_csum(sb))
flex_gd->bg_flags[i] = EXT4_BG_BLOCK_UNINIT |
EXT4_BG_INODE_UNINIT;
else
flex_gd->bg_flags[i] = EXT4_BG_INODE_ZEROED;
}

- if (last_group == n_group &&
- EXT4_HAS_RO_COMPAT_FEATURE(sb,
- EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
+ if (last_group == n_group && ext4_has_group_desc_csum(sb))
/* We need to initialize block bitmap of last group. */
flex_gd->bg_flags[i - 1] &= ~EXT4_BG_BLOCK_UNINIT;

diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index 2190044..6196bfa 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -2097,9 +2097,7 @@ static __le16 ext4_group_desc_csum(struct ext4_sb_info *sbi, __u32 block_group,
__le32 le_group = cpu_to_le32(block_group);

if ((sbi->s_es->s_feature_ro_compat &
- cpu_to_le32(EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) &&
- (sbi->s_es->s_feature_incompat &
- cpu_to_le32(EXT4_FEATURE_INCOMPAT_BG_USE_META_CSUM))) {
+ cpu_to_le32(EXT4_FEATURE_RO_COMPAT_METADATA_CSUM))) {
/* Use new metadata_csum algorithm */
__u16 old_csum;
__u32 csum32;
@@ -2135,24 +2133,23 @@ out:
return cpu_to_le16(crc);
}

-int ext4_group_desc_csum_verify(struct ext4_sb_info *sbi, __u32 block_group,
+int ext4_group_desc_csum_verify(struct super_block *sb, __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)))
+ if (ext4_has_group_desc_csum(sb) &&
+ (gdp->bg_checksum != ext4_group_desc_csum(EXT4_SB(sb),
+ block_group, gdp)))
return 0;

return 1;
}

-void ext4_group_desc_csum_set(struct ext4_sb_info *sbi, __u32 block_group,
+void ext4_group_desc_csum_set(struct super_block *sb, __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)))
+ if (!ext4_has_group_desc_csum(sb))
return;
- gdp->bg_checksum = ext4_group_desc_csum(sbi, block_group, gdp);
+ gdp->bg_checksum = ext4_group_desc_csum(EXT4_SB(sb), block_group, gdp);
}

/* Called at mount-time, super-block is locked */
@@ -2209,7 +2206,7 @@ static int ext4_check_descriptors(struct super_block *sb,
return 0;
}
ext4_lock_group(sb, i);
- if (!ext4_group_desc_csum_verify(sbi, i, gdp)) {
+ if (!ext4_group_desc_csum_verify(sb, i, gdp)) {
ext4_msg(sb, KERN_ERR, "ext4_check_descriptors: "
"Checksum for group %u failed (%u!=%u)",
i, le16_to_cpu(ext4_group_desc_csum(sbi, i,
@@ -4620,7 +4617,7 @@ static int ext4_remount(struct super_block *sb, int *flags, char *data)
struct ext4_group_desc *gdp =
ext4_get_group_desc(sb, g, NULL);

- if (!ext4_group_desc_csum_verify(sbi, g, gdp)) {
+ if (!ext4_group_desc_csum_verify(sb, g, gdp)) {
ext4_msg(sb, KERN_ERR,
"ext4_remount: Checksum for group %u failed (%u!=%u)",
g, le16_to_cpu(ext4_group_desc_csum(sbi, g, gdp)),


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