[RFC ONLY 20/23] btrfs: reuse encrypted filename hash when possible.

[Sweet Tea Dorminy <sweettea-kernel@dorminy.me>]

From: Omar Sandoval <osandov@osandov.com>

For encrypted fscrypt_names, we can reuse fscrypt's precomputed hash of
the encrypted name to generate our own hash, instead of rehashing the
unencrypted name (which may not be possible if it's a nokey name).

Signed-off-by: Sweet Tea Dorminy <sweettea-kernel@dorminy.me>
---
 fs/btrfs/ctree.h | 21 ++++++++++++++++++---
 1 file changed, 18 insertions(+), 3 deletions(-)

diff --git a/fs/btrfs/ctree.h b/fs/btrfs/ctree.h
index 522bb3452768..2c6baf6cd718 100644
--- a/fs/btrfs/ctree.h
+++ b/fs/btrfs/ctree.h
@@ -2775,7 +2775,10 @@ static inline void btrfs_crc32c_final(u32 crc, u8 *result)
 
 static inline u64 btrfs_name_hash(struct fscrypt_name *name)
 {
-	return crc32c((u32)~1, fname_name(name), fname_len(name));
+	if (fname_name(name))
+		return crc32c((u32)~1, fname_name(name), fname_len(name));
+	else
+		return name->hash | ((u64)name->minor_hash << 32);
 }
 
 /*
@@ -2784,8 +2787,20 @@ static inline u64 btrfs_name_hash(struct fscrypt_name *name)
 static inline u64 btrfs_extref_hash(u64 parent_objectid,
 				    struct fscrypt_name *name)
 {
-	return (u64) crc32c(parent_objectid, fname_name(name),
-			    fname_len(name));
+	/*
+	 * If the name is encrypted and we don't have the key, we can use the
+	 * fscrypt-provided hash instead of the normal name, and do the steps
+	 * of crc32c() manually. Else, just hash the name, parent objectid,
+	 * and name length.
+	 */
+	if (fname_name(name))
+		return (u64) crc32c(parent_objectid, fname_name(name),
+				    fname_len(name));
+	else
+		return (__crc32c_le_combine(parent_objectid,
+					    name->hash,
+					    fname_len(name)) ^
+			__crc32c_le_shift(~1, fname_len(name)));
 }
 
 static inline gfp_t btrfs_alloc_write_mask(struct address_space *mapping)
-- 
2.35.1