[PATCH v2 1/3] libfs: Add generic function for setting dentry_ops

[Daniel Rosenberg]

This adds a function to set dentry operations at lookup time that will
work for both encrypted filenames and casefolded filenames.

A filesystem that supports both features simultaneously can use this
function during lookup preparations to set up its dentry operations once
fscrypt no longer does that itself.

Currently the casefolding dentry operation are always set if the
filesystem defines an encoding because the features is toggleable on
empty directories. Since we don't know what set of functions we'll
eventually need, and cannot change them later, we add just add them.

Signed-off-by: Daniel Rosenberg <drosen at google.com>
---
 fs/libfs.c         | 60 ++++++++++++++++++++++++++++++++++++++++++++++
 include/linux/fs.h |  1 +
 2 files changed, 61 insertions(+)

diff --git a/fs/libfs.c b/fs/libfs.c
index fc34361c1489..dd8504f3ff5d 100644
--- a/fs/libfs.c
+++ b/fs/libfs.c
@@ -1449,4 +1449,64 @@ int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str)
 	return 0;
 }
 EXPORT_SYMBOL(generic_ci_d_hash);
+
+static const struct dentry_operations generic_ci_dentry_ops = {
+	.d_hash = generic_ci_d_hash,
+	.d_compare = generic_ci_d_compare,
+};
 #endif
+
+#ifdef CONFIG_FS_ENCRYPTION
+static const struct dentry_operations generic_encrypted_dentry_ops = {
+	.d_revalidate = fscrypt_d_revalidate,
+};
+#endif
+
+#if IS_ENABLED(CONFIG_UNICODE) && IS_ENABLED(CONFIG_FS_ENCRYPTION)
+static const struct dentry_operations generic_encrypted_ci_dentry_ops = {
+	.d_hash = generic_ci_d_hash,
+	.d_compare = generic_ci_d_compare,
+	.d_revalidate = fscrypt_d_revalidate,
+};
+#endif
+
+/**
+ * generic_set_encrypted_ci_d_ops - helper for setting d_ops for given dentry
+ * @dentry:	dentry to set ops on
+ *
+ * This function sets the dentry ops for the given dentry to handle both
+ * casefolded and encrypted dentry names.
+ *
+ * Encryption requires d_revalidate to remove nokey names once the key is present.
+ * Casefolding is toggleable on an empty directory. Since we can't change the
+ * operations later on, we just add the casefolding ops if the filesystem defines an
+ * encoding.
+ */
+void generic_set_encrypted_ci_d_ops(struct dentry *dentry)
+{
+#ifdef CONFIG_FS_ENCRYPTION
+	bool needs_encrypt_ops = dentry->d_flags & DCACHE_NOKEY_NAME;
+#endif
+#ifdef CONFIG_UNICODE
+	bool needs_ci_ops = dentry->d_sb->s_encoding;
+#endif
+#if defined(CONFIG_FS_ENCRYPTION) && defined(CONFIG_UNICODE)
+	if (needs_encrypt_ops && needs_ci_ops) {
+		d_set_d_op(dentry, &generic_encrypted_ci_dentry_ops);
+			return;
+	}
+#endif
+#ifdef CONFIG_FS_ENCRYPTION
+	if (needs_encrypt_ops) {
+		d_set_d_op(dentry, &generic_encrypted_dentry_ops);
+		return;
+	}
+#endif
+#ifdef CONFIG_UNICODE
+	if (needs_ci_ops) {
+		d_set_d_op(dentry, &generic_ci_dentry_ops);
+		return;
+	}
+#endif
+}
+EXPORT_SYMBOL(generic_set_encrypted_ci_d_ops);
diff --git a/include/linux/fs.h b/include/linux/fs.h
index 8667d0cdc71e..11345e66353b 100644
--- a/include/linux/fs.h
+++ b/include/linux/fs.h
@@ -3202,6 +3202,7 @@ extern int generic_ci_d_hash(const struct dentry *dentry, struct qstr *str);
 extern int generic_ci_d_compare(const struct dentry *dentry, unsigned int len,
 				const char *str, const struct qstr *name);
 #endif
+extern void generic_set_encrypted_ci_d_ops(struct dentry *dentry);
 
 #ifdef CONFIG_MIGRATION
 extern int buffer_migrate_page(struct address_space *,
-- 
2.29.2.299.gdc1121823c-goog