1 files changed, 37 insertions, 3 deletions

diff --git a/include/linux/fscrypt.h b/include/linux/fscrypt.h
index 10dd161690a2..516aba5b858b 100644
--- a/include/linux/fscrypt.h
+++ b/include/linux/fscrypt.h
@@ -61,6 +61,12 @@ struct fscrypt_name {
 
 /* Crypto operations for filesystems */
 struct fscrypt_operations {
+	/*
+	 * The offset of the pointer to struct fscrypt_inode_info in the
+	 * filesystem-specific part of the inode, relative to the beginning of
+	 * the common part of the inode (the 'struct inode').
+	 */
+	ptrdiff_t inode_info_offs;
 
 	/*
 	 * If set, then fs/crypto/ will allocate a global bounce page pool the
@@ -195,16 +201,44 @@ struct fscrypt_operations {
 int fscrypt_d_revalidate(struct inode *dir, const struct qstr *name,
 			 struct dentry *dentry, unsigned int flags);
 
+/*
+ * Returns the address of the fscrypt info pointer within the
+ * filesystem-specific part of the inode.  (To save memory on filesystems that
+ * don't support fscrypt, a field in 'struct inode' itself is no longer used.)
+ */
+static inline struct fscrypt_inode_info **
+fscrypt_inode_info_addr(const struct inode *inode)
+{
+	VFS_WARN_ON_ONCE(inode->i_sb->s_cop->inode_info_offs == 0);
+	return (void *)inode + inode->i_sb->s_cop->inode_info_offs;
+}
+
+/*
+ * Load the inode's fscrypt info pointer, using a raw dereference.  Since this
+ * uses a raw dereference with no memory barrier, it is appropriate to use only
+ * when the caller knows the inode's key setup already happened, resulting in
+ * non-NULL fscrypt info.  E.g., the file contents en/decryption functions use
+ * this, since fscrypt_file_open() set up the key.
+ */
+static inline struct fscrypt_inode_info *
+fscrypt_get_inode_info_raw(const struct inode *inode)
+{
+	struct fscrypt_inode_info *ci = *fscrypt_inode_info_addr(inode);
+
+	VFS_WARN_ON_ONCE(ci == NULL);
+	return ci;
+}
+
 static inline struct fscrypt_inode_info *
 fscrypt_get_inode_info(const struct inode *inode)
 {
 	/*
 	 * Pairs with the cmpxchg_release() in fscrypt_setup_encryption_info().
-	 * I.e., another task may publish ->i_crypt_info concurrently, executing
-	 * a RELEASE barrier.  We need to use smp_load_acquire() here to safely
+	 * I.e., another task may publish the fscrypt info concurrently,
+	 * executing a RELEASE barrier.  Use smp_load_acquire() here to safely
 	 * ACQUIRE the memory the other task published.
 	 */
-	return smp_load_acquire(&inode->i_crypt_info);
+	return smp_load_acquire(fscrypt_inode_info_addr(inode));
 }
 
 /**