[PATCH v2 2/4] btrfs: assign checksum shash slots on init

[David Sterba <dsterba@suse.com>]

When initializing checksum implementation on first mount, assign it to
the proper slot based on the driver name. If it contains "generic" it's
considered the non-accelerated one. Based on that properly set the
BTRFS_FS_CSUM_IMPL_FAST bit, previously it could be mistakenly set as
fast despite a different checksum (eg. sha256) with generic
implementation.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 fs/btrfs/disk-io.c | 13 ++++++++++++-
 fs/btrfs/super.c   |  2 --
 2 files changed, 12 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3c2251199f0c..247187427760 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2430,7 +2430,18 @@ static int btrfs_init_csum_hash(struct btrfs_fs_info *fs_info, u16 csum_type)
 		return PTR_ERR(csum_shash);
 	}
 
-	fs_info->csum_shash[CSUM_DEFAULT] = csum_shash;
+	/*
+	 * Find the fastest implementation available, but keep the slots
+	 * matching the type.
+	 */
+	if (strstr(crypto_shash_driver_name(fs_info->csum_shash[CSUM_DEFAULT]),
+		   "generic") != NULL) {
+		fs_info->csum_shash[CSUM_GENERIC] = csum_shash;
+		clear_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags);
+	} else {
+		fs_info->csum_shash[CSUM_ACCEL] = csum_shash;
+		set_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags);
+	}
 
 	btrfs_info(fs_info, "using %s (%s) checksum algorithm",
 			btrfs_super_csum_name(csum_type),
diff --git a/fs/btrfs/super.c b/fs/btrfs/super.c
index 1032aaa2c2f4..595b8d92ef86 100644
--- a/fs/btrfs/super.c
+++ b/fs/btrfs/super.c
@@ -1819,8 +1819,6 @@ static struct dentry *btrfs_mount_root(struct file_system_type *fs_type,
 	} else {
 		snprintf(s->s_id, sizeof(s->s_id), "%pg", bdev);
 		btrfs_sb(s)->bdev_holder = fs_type;
-		if (!strstr(crc32c_impl(), "generic"))
-			set_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags);
 		error = btrfs_fill_super(s, fs_devices, data);
 	}
 	if (!error)
-- 
2.36.1