[PATCH v2 2/3] ext4: add support for IV_INO_LBLK_64 encryption policies

[Eric Biggers <ebiggers@kernel.org>]

From: Eric Biggers <ebiggers@google.com>

IV_INO_LBLK_64 encryption policies have special requirements from the
filesystem beyond those of the existing encryption policies:

- Inode numbers must never change, even if the filesystem is resized.
- Inode numbers must be <= 32 bits.
- File logical block numbers must be <= 32 bits.

ext4 has 32-bit inode and file logical block numbers.  However,
resize2fs can re-number inodes when shrinking an ext4 filesystem.

However, typically the people who would want to use this format don't
care about filesystem shrinking.  They'd be fine with a solution that
just prevents the filesystem from being shrunk.

Therefore, add a new feature flag EXT4_FEATURE_COMPAT_STABLE_INODES that
will do exactly that.  Then wire up the fscrypt_operations to expose
this flag to fs/crypto/, so that it allows IV_INO_LBLK_64 policies when
this flag is set.

Signed-off-by: Eric Biggers <ebiggers@google.com>
---
 fs/ext4/ext4.h  |  2 ++
 fs/ext4/super.c | 14 ++++++++++++++
 2 files changed, 16 insertions(+)

diff --git a/fs/ext4/ext4.h b/fs/ext4/ext4.h
index 03db3e71676ce..b3a2cc7c0252f 100644
--- a/fs/ext4/ext4.h
+++ b/fs/ext4/ext4.h
@@ -1678,6 +1678,7 @@ static inline bool ext4_verity_in_progress(struct inode *inode)
 #define EXT4_FEATURE_COMPAT_RESIZE_INODE	0x0010
 #define EXT4_FEATURE_COMPAT_DIR_INDEX		0x0020
 #define EXT4_FEATURE_COMPAT_SPARSE_SUPER2	0x0200
+#define EXT4_FEATURE_COMPAT_STABLE_INODES	0x0800
 
 #define EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER	0x0001
 #define EXT4_FEATURE_RO_COMPAT_LARGE_FILE	0x0002
@@ -1779,6 +1780,7 @@ EXT4_FEATURE_COMPAT_FUNCS(xattr,		EXT_ATTR)
 EXT4_FEATURE_COMPAT_FUNCS(resize_inode,		RESIZE_INODE)
 EXT4_FEATURE_COMPAT_FUNCS(dir_index,		DIR_INDEX)
 EXT4_FEATURE_COMPAT_FUNCS(sparse_super2,	SPARSE_SUPER2)
+EXT4_FEATURE_COMPAT_FUNCS(stable_inodes,	STABLE_INODES)
 
 EXT4_FEATURE_RO_COMPAT_FUNCS(sparse_super,	SPARSE_SUPER)
 EXT4_FEATURE_RO_COMPAT_FUNCS(large_file,	LARGE_FILE)
diff --git a/fs/ext4/super.c b/fs/ext4/super.c
index dd654e53ba3d9..b3cbf8622eab6 100644
--- a/fs/ext4/super.c
+++ b/fs/ext4/super.c
@@ -1345,6 +1345,18 @@ static bool ext4_dummy_context(struct inode *inode)
 	return DUMMY_ENCRYPTION_ENABLED(EXT4_SB(inode->i_sb));
 }
 
+static bool ext4_has_stable_inodes(struct super_block *sb)
+{
+	return ext4_has_feature_stable_inodes(sb);
+}
+
+static void ext4_get_ino_and_lblk_bits(struct super_block *sb,
+				       int *ino_bits_ret, int *lblk_bits_ret)
+{
+	*ino_bits_ret = 8 * sizeof(EXT4_SB(sb)->s_es->s_inodes_count);
+	*lblk_bits_ret = 8 * sizeof(ext4_lblk_t);
+}
+
 static const struct fscrypt_operations ext4_cryptops = {
 	.key_prefix		= "ext4:",
 	.get_context		= ext4_get_context,
@@ -1352,6 +1364,8 @@ static const struct fscrypt_operations ext4_cryptops = {
 	.dummy_context		= ext4_dummy_context,
 	.empty_dir		= ext4_empty_dir,
 	.max_namelen		= EXT4_NAME_LEN,
+	.has_stable_inodes	= ext4_has_stable_inodes,
+	.get_ino_and_lblk_bits	= ext4_get_ino_and_lblk_bits,
 };
 #endif
 
-- 
2.24.0.rc0.303.g954a862665-goog