ext4: load the crc32c driver if necessary

Obtain a reference to the cryptoapi and crc32c if we mount a
filesystem with metadata checksumming enabled.

Signed-off-by: Darrick J. Wong <[e-mail]>
Signed-off-by: "Theodore Ts'o" <[e-mail]>

fs/ext4/Kconfig

···
 	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.
 

fs/ext4/ext4.h

···
 #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
···
 
 	/* record the last minlen when FITRIM is called. */
 	atomic_t s_last_trim_minblks;
+
+	/* 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)
···
 #define DX_HASH_LEGACY_UNSIGNED	3
 #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__
 

fs/ext4/super.c

···
 	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);
 }
···
 		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)) {
+			ext4_msg(sb, KERN_ERR, "Cannot load crc32c 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);
···
 		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("options", sbi->s_proc);
 		remove_proc_entry(sb->s_id, ext4_proc_root);