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Date:	Fri, 2 Mar 2012 19:56:13 -0800
From:	"Darrick J. Wong" <djwong@...ibm.com>
To:	Andreas Dilger <adilger.kernel@...ger.ca>
Cc:	"Ted Ts'o" <tytso@....edu>,
	Sunil Mushran <sunil.mushran@...cle.com>,
	Martin K Petersen <martin.petersen@...cle.com>,
	Greg Freemyer <greg.freemyer@...il.com>,
	Amir Goldstein <amir73il@...il.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	Andi Kleen <andi@...stfloor.org>,
	Mingming Cao <cmm@...ibm.com>,
	Joel Becker <jlbec@...lplan.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>,
	linux-ext4@...r.kernel.org, Coly Li <colyli@...il.com>
Subject: [RFC v2] ext4: Rework metadata_csum/gdt_csum flag handling in
	kernel

On Tue, Feb 28, 2012 at 10:48:16PM -0700, Andreas Dilger wrote:
> On 2012-02-28, at 6:32 PM, Darrick J. Wong wrote:
> > 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...?
> 
> As with the e2fsprogs patch, I think METADATA_CSUM should override GDT_CSUM
> completely.  If both are set, then the kernel should ignore GDT_CSUM entirely
> and just use the new checksum algorithm for the group descriptors.  It is up
> to the user tools not to allow this combination of features to be set, and
> there is no value in adding an extra failure case if they are (though if the
> superblock checksum is also incorrect, that means the superblock is broken
> and a backup should be used and/or the mount failed).
> 
> > Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
> > ---
> 
> One minor comment below, but I think this patch is the right approach.  I was
> also going to proffer my Acked-by: for this patch, but I now recall that this
> patch is itself short lived and will be merged into the patch series.

I merged that comment into the kernel patch, along with an extra hunk to warn
if metadata_csum and uninit_bg feature bits are both set.  I wonder if the
kernel should react more forcefully to this supposedly "impossible" situation?
But then I might just be unnecessarily paranoid.  At worst, I suppose, the
checksums on all the group descriptors will be "wrong" and the fs simply won't
allow writes.

(Hm, maybe it should unclear the clean flag?)

Here's v2, to go with the e2fsprogs v2 patch.

Signed-off-by: Darrick J. Wong <djwong@...ibm.com>
---

 fs/ext4/balloc.c  |    4 ++--
 fs/ext4/ext4.h    |   21 ++++++++++++++++-----
 fs/ext4/ialloc.c  |   19 ++++++++-----------
 fs/ext4/inode.c   |    3 +--
 fs/ext4/mballoc.c |    6 +++---
 fs/ext4/resize.c  |    9 +++------
 fs/ext4/super.c   |   30 +++++++++++++++++-------------
 7 files changed, 50 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..dd75078 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1434,6 +1434,12 @@ 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 also enables group descriptor checksums (GDT_CSUM).  When
+ * METADATA_CSUM is set, group descriptor checksums use the same algorithm as
+ * all other data structures' checksums.  However, the METADATA_CSUM and
+ * GDT_CSUM bits are mutually exclusive.
+ */
 #define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM	0x0400
 
 #define EXT4_FEATURE_INCOMPAT_COMPRESSION	0x0001
@@ -1449,7 +1455,6 @@ 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 +1478,7 @@ 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 +2096,18 @@ 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..e9b01e4 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,
@@ -3289,6 +3286,13 @@ static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		goto cantfind_ext4;
 	sbi->s_kbytes_written = le64_to_cpu(es->s_kbytes_written);
 
+	/* Warn if metadata_csum and gdt_csum are both set. */
+	if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
+				       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM) &&
+	    EXT4_HAS_RO_COMPAT_FEATURE(sb, EXT4_FEATURE_RO_COMPAT_GDT_CSUM))
+		ext4_warning(sb, KERN_INFO "metadata_csum and uninit_bg are "
+			     "redundant flags; please run fsck.");
+
 	/* Check for a known checksum algorithm */
 	if (!ext4_verify_csum_type(sb, es)) {
 		ext4_msg(sb, KERN_ERR, "VFS: Found ext4 filesystem with "
@@ -4620,7 +4624,7 @@ 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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