ceph: move crypt info pointer to fs-specific part of inode

Move the fscrypt_inode_info pointer into the filesystem-specific part of
the inode by adding the field ceph_inode_info::i_crypt_info and
configuring fscrypt_operations::inode_info_offs accordingly.

This is a prerequisite for a later commit that removes
inode::i_crypt_info, saving memory and improving cache efficiency with
filesystems that don't support fscrypt.

Co-developed-by: Christian Brauner <brauner@kernel.org>
Signed-off-by: Eric Biggers <ebiggers@kernel.org>
Link: https://lore.kernel.org/20250810075706.172910-7-ebiggers@kernel.org
Signed-off-by: Christian Brauner <brauner@kernel.org>

Author: Eric Biggers

fs/ceph/crypto.c

@@ -133,6 +133,8 @@ static const union fscrypt_policy *ceph_get_dummy_policy(struct super_block *sb)
 }
 
 static struct fscrypt_operations ceph_fscrypt_ops = {
+	.inode_info_offs	= (int)offsetof(struct ceph_inode_info, i_crypt_info) -
+				  (int)offsetof(struct ceph_inode_info, netfs.inode),
 	.needs_bounce_pages	= 1,
 	.get_context		= ceph_crypt_get_context,
 	.set_context		= ceph_crypt_set_context,

fs/ceph/inode.c

@@ -665,6 +665,7 @@ struct inode *ceph_alloc_inode(struct super_block *sb)
 	ci->i_work_mask = 0;
 	memset(&ci->i_btime, '\0', sizeof(ci->i_btime));
 #ifdef CONFIG_FS_ENCRYPTION
+	ci->i_crypt_info = NULL;
 	ci->fscrypt_auth = NULL;
 	ci->fscrypt_auth_len = 0;
 #endif

fs/ceph/super.h

@@ -463,6 +463,7 @@ struct ceph_inode_info {
 	unsigned long  i_work_mask;
 
 #ifdef CONFIG_FS_ENCRYPTION
+	struct fscrypt_inode_info *i_crypt_info;
 	u32 fscrypt_auth_len;
 	u32 fscrypt_file_len;
 	u8 *fscrypt_auth;