Patchwork [04/22] ext4: Only call out to crc32c if necessary

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Submitter Darrick J. Wong
Date Nov. 28, 2011, 11:26 p.m.
Message ID <20111128232642.19194.80905.stgit@elm3c44.beaverton.ibm.com>
Download mbox | patch
Permalink /patch/128119/
State Superseded
Headers show

Comments

Darrick J. Wong - Nov. 28, 2011, 11:26 p.m.
Only obtain a reference to the cryptoapi and crc32c if we happen to mount a
filesystem with metadata checksumming enabled.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
---
 fs/ext4/Kconfig |    2 ++
 fs/ext4/ext4.h  |   23 +++++++++++++++++++++++
 fs/ext4/super.c |   15 +++++++++++++++
 3 files changed, 40 insertions(+), 0 deletions(-)



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Theodore Ts'o - Dec. 5, 2011, 3:52 p.m.
On Mon, Nov 28, 2011 at 03:26:43PM -0800, Darrick J. Wong wrote:
> +	/* Load the checksum driver */
> +	if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
> +				       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
> +		sbi->s_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
> +		if (IS_ERR(sbi->s_chksum_driver)) {
> +			ret = PTR_ERR(sbi->s_chksum_driver);
> +			sbi->s_chksum_driver = NULL;
> +			goto failed_mount;
> +		}
> +	}

Unless the crypto engine printk's a message if the crc32c algorithm is
not available (perhaps even if it does), it's probably going to be a
good idea to issue an ext4_msg() saying that we're failing because we
couldn't load the crc32c crypto module.  Otherwise the user will get a
mysterious failure (including a message from mount to check 'dmesg |
tail'), and then when they look at the kernel messages, they won't see
what might have gone wrong, and then they'll send a complaint to
ext3-users or linux-ext4....

						- Ted
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Darrick J. Wong - Dec. 5, 2011, 7:38 p.m.
On Mon, Dec 05, 2011 at 10:52:26AM -0500, Ted Ts'o wrote:
> On Mon, Nov 28, 2011 at 03:26:43PM -0800, Darrick J. Wong wrote:
> > +	/* Load the checksum driver */
> > +	if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
> > +				       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
> > +		sbi->s_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
> > +		if (IS_ERR(sbi->s_chksum_driver)) {
> > +			ret = PTR_ERR(sbi->s_chksum_driver);
> > +			sbi->s_chksum_driver = NULL;
> > +			goto failed_mount;
> > +		}
> > +	}
> 
> Unless the crypto engine printk's a message if the crc32c algorithm is
> not available (perhaps even if it does), it's probably going to be a
> good idea to issue an ext4_msg() saying that we're failing because we
> couldn't load the crc32c crypto module.  Otherwise the user will get a
> mysterious failure (including a message from mount to check 'dmesg |
> tail'), and then when they look at the kernel messages, they won't see
> what might have gone wrong, and then they'll send a complaint to
> ext3-users or linux-ext4....

Ok.

--D

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Patch

diff --git a/fs/ext4/Kconfig b/fs/ext4/Kconfig
index 9ed1bb1..c22f170 100644
--- a/fs/ext4/Kconfig
+++ b/fs/ext4/Kconfig
@@ -2,6 +2,8 @@  config EXT4_FS
 	tristate "The Extended 4 (ext4) filesystem"
 	select JBD2
 	select CRC16
+	select CRYPTO
+	select CRYPTO_CRC32C
 	help
 	  This is the next generation of the ext3 filesystem.
 
diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index e496e72..eab64c2 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -29,6 +29,7 @@ 
 #include <linux/wait.h>
 #include <linux/blockgroup_lock.h>
 #include <linux/percpu_counter.h>
+#include <crypto/hash.h>
 #ifdef __KERNEL__
 #include <linux/compat.h>
 #endif
@@ -1255,6 +1256,9 @@  struct ext4_sb_info {
 
 	/* Precomputed FS UUID checksum */
 	__u32 s_uuid_csum;
+
+	/* Reference to checksum algorithm driver via cryptoapi */
+	struct crypto_shash *s_chksum_driver;
 };
 
 static inline struct ext4_sb_info *EXT4_SB(struct super_block *sb)
@@ -1596,6 +1600,25 @@  static inline __le16 ext4_rec_len_to_disk(unsigned len, unsigned blocksize)
 #define DX_HASH_HALF_MD4_UNSIGNED	4
 #define DX_HASH_TEA_UNSIGNED		5
 
+static inline u32 ext4_chksum(struct ext4_sb_info *sbi, u32 crc,
+			      const void *address, unsigned int length)
+{
+	struct {
+		struct shash_desc shash;
+		char ctx[crypto_shash_descsize(sbi->s_chksum_driver)];
+	} desc;
+	int err;
+
+	desc.shash.tfm = sbi->s_chksum_driver;
+	desc.shash.flags = 0;
+	*(u32 *)desc.ctx = crc;
+
+	err = crypto_shash_update(&desc.shash, address, length);
+	BUG_ON(err);
+
+	return *(u32 *)desc.ctx;
+}
+
 #ifdef __KERNEL__
 
 /* hash info structure used by the directory hash */
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index a56c14e..a555811 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -887,6 +887,8 @@  static void ext4_put_super(struct super_block *sb)
 	unlock_super(sb);
 	kobject_put(&sbi->s_kobj);
 	wait_for_completion(&sbi->s_kobj_unregister);
+	if (sbi->s_chksum_driver)
+		crypto_free_shash(sbi->s_chksum_driver);
 	kfree(sbi->s_blockgroup_lock);
 	kfree(sbi);
 }
@@ -3200,6 +3202,17 @@  static int ext4_fill_super(struct super_block *sb, void *data, int silent)
 		goto cantfind_ext4;
 	}
 
+	/* Load the checksum driver */
+	if (EXT4_HAS_RO_COMPAT_FEATURE(sb,
+				       EXT4_FEATURE_RO_COMPAT_METADATA_CSUM)) {
+		sbi->s_chksum_driver = crypto_alloc_shash("crc32c", 0, 0);
+		if (IS_ERR(sbi->s_chksum_driver)) {
+			ret = PTR_ERR(sbi->s_chksum_driver);
+			sbi->s_chksum_driver = NULL;
+			goto failed_mount;
+		}
+	}
+
 	/* Set defaults before we parse the mount options */
 	def_mount_opts = le32_to_cpu(es->s_default_mount_opts);
 	set_opt(sb, INIT_INODE_TABLE);
@@ -3880,6 +3893,8 @@  failed_mount2:
 		brelse(sbi->s_group_desc[i]);
 	ext4_kvfree(sbi->s_group_desc);
 failed_mount:
+	if (sbi->s_chksum_driver)
+		crypto_free_shash(sbi->s_chksum_driver);
 	if (sbi->s_proc) {
 		remove_proc_entry(sb->s_id, ext4_proc_root);
 	}