linux-ext4 - [PATCH 06/20] nls: Add support for multiple versions of an encoding

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Date:   Tue,  3 Jul 2018 13:06:46 -0400
From:   Gabriel Krisman Bertazi <krisman@...labora.co.uk>
To:     tytso@....edu
Cc:     linux-ext4@...r.kernel.org, darrick.wong@...cle.com,
        kernel@...labora.com,
        Gabriel Krisman Bertazi <krisman@...labora.co.uk>
Subject: [PATCH 06/20] nls: Add support for multiple versions of an encoding

NLS charsets wanting to use this feature can implement the load_create()
hook, which creates a nls_table for that specific encoding version.  The
charset code is responsible for freeing the table memory when the module
is removed.

Signed-off-by: Gabriel Krisman Bertazi <krisman@...labora.co.uk>
---
 fs/nls/nls_core.c   | 45 ++++++++++++++++++++++++++++++++++++++-------
 include/linux/nls.h |  5 +++++
 2 files changed, 43 insertions(+), 7 deletions(-)

diff --git a/fs/nls/nls_core.c b/fs/nls/nls_core.c
index 200a7f8165e6..19a5a66fe423 100644
--- a/fs/nls/nls_core.c
+++ b/fs/nls/nls_core.c
@@ -19,10 +19,27 @@
 extern struct nls_charset default_charset;
 static struct nls_charset *charsets = &default_charset;
 static DEFINE_SPINLOCK(nls_lock);
-static struct nls_table *nls_load_table(struct nls_charset *charset)
+
+static struct nls_table *nls_load_table(struct nls_charset *charset,
+					const char *version)
 {
-	/* For now, return the default table, which is the first one found. */
-	return charset->tables;
+	struct nls_table *tbl;
+
+	if (!charset->load_table) {
+		/* If there is no table_create, only 1 table is
+		 * supported and it must have been loaded
+		 * statically.
+		 */
+		return charset->tables;
+	}
+
+	tbl = charset->load_table(version);
+	if (!tbl) {
+		/* Invalid version */
+		return ERR_PTR(-EINVAL);
+	}
+
+	return tbl;
 }
 
 int __register_nls(struct nls_charset *nls, struct module *owner)
@@ -85,21 +102,35 @@ static struct nls_charset *find_nls(const char *charset)
 	return nls;
 }
 
-struct nls_table *load_nls(char *charset)
+struct nls_table *load_nls_version(const char *charset, const char *version)
 {
 	struct nls_charset *nls_charset;
 
 	nls_charset = try_then_request_module(find_nls(charset),
 					      "nls_%s", charset);
-	if (!IS_ERR(nls_charset))
+	if (IS_ERR(nls_charset))
+		return ERR_PTR(-EINVAL);
+
+	return nls_load_table(nls_charset, version);
+}
+EXPORT_SYMBOL(load_nls_version);
+
+struct nls_table *load_nls(char *charset)
+{
+	struct nls_table *table = load_nls_version(charset, NULL);
+
+	/* Pre-versioned load_nls() didn't return error pointers. Let's
+	 * keep the abi for now to prevent breakage.
+	 */
+	if (IS_ERR(table))
 		return NULL;
 
-	return nls_load_table(nls_charset);
+	return table;
 }
 
 void unload_nls(struct nls_table *nls)
 {
-	if (nls)
+	if (!IS_ERR_OR_NULL(nls))
 		module_put(nls->charset->owner);
 }
 
diff --git a/include/linux/nls.h b/include/linux/nls.h
index cdc95cd9e5d4..e422bd52afbb 100644
--- a/include/linux/nls.h
+++ b/include/linux/nls.h
@@ -30,6 +30,8 @@ struct nls_ops {
 
 struct nls_table {
 	const struct nls_charset *charset;
+	unsigned int version;
+
 	const struct nls_ops *ops;
 	const unsigned char *charset2lower;
 	const unsigned char *charset2upper;
@@ -42,6 +44,7 @@ struct nls_charset {
 	struct module *owner;
 	struct nls_table *tables;
 	struct nls_charset *next;
+	struct nls_table *(*load_table)(const char *version);
 };
 
 /* this value hold the maximum octet of charset */
@@ -58,6 +61,8 @@ enum utf16_endian {
 extern int __register_nls(struct nls_charset *, struct module *);
 extern int unregister_nls(struct nls_charset *);
 extern struct nls_table *load_nls(char *);
+extern struct nls_table *load_nls_version(const char *charset,
+					  const char *version);
 extern void unload_nls(struct nls_table *);
 extern struct nls_table *load_nls_default(void);
 #define register_nls(nls) __register_nls((nls), THIS_MODULE)
-- 
2.18.0