vfs: Convert tracefs to use the new mount API

Convert the tracefs filesystem to the new internal mount API as the old
one will be obsoleted and removed.  This allows greater flexibility in
communication of mount parameters between userspace, the VFS and the
filesystem.

See Documentation/filesystems/mount_api.txt for more information.
Signed-off-by: David Howells <dhowells@redhat.com>
Co-developed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
[sandeen: forward port to modern kernel, fix remounting]
Link: https://lore.kernel.org/r/536e99d3-345c-448b-adee-a21389d7ab4b@redhat.com
cc: Steven Rostedt <rostedt@goodmis.org>
cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Christian Brauner <brauner@kernel.org>

fs/tracefs/inode.c

@@ -11,14 +11,14 @@
 
 #include <linux/module.h>
 #include <linux/fs.h>
-#include <linux/mount.h>
+#include <linux/fs_context.h>
+#include <linux/fs_parser.h>
 #include <linux/kobject.h>
 #include <linux/namei.h>
 #include <linux/tracefs.h>
 #include <linux/fsnotify.h>
 #include <linux/security.h>
 #include <linux/seq_file.h>
-#include <linux/parser.h>
 #include <linux/magic.h>
 #include <linux/slab.h>
 #include "internal.h"
@@ -231,7 +231,7 @@ struct inode *tracefs_get_inode(struct super_block *sb)
 	return inode;
 }
 
-struct tracefs_mount_opts {
+struct tracefs_fs_info {
 	kuid_t uid;
 	kgid_t gid;
 	umode_t mode;
@@ -243,68 +243,51 @@ enum {
 	Opt_uid,
 	Opt_gid,
 	Opt_mode,
-	Opt_err
 };
 
-static const match_table_t tokens = {
-	{Opt_uid, "uid=%u"},
-	{Opt_gid, "gid=%u"},
-	{Opt_mode, "mode=%o"},
-	{Opt_err, NULL}
+static const struct fs_parameter_spec tracefs_param_specs[] = {
+	fsparam_u32	("gid",		Opt_gid),
+	fsparam_u32oct	("mode",	Opt_mode),
+	fsparam_u32	("uid",		Opt_uid),
+	{}
 };
 
-struct tracefs_fs_info {
-	struct tracefs_mount_opts mount_opts;
-};
-
-static int tracefs_parse_options(char *data, struct tracefs_mount_opts *opts)
+static int tracefs_parse_param(struct fs_context *fc, struct fs_parameter *param)
 {
-	substring_t args[MAX_OPT_ARGS];
-	int option;
-	int token;
+	struct tracefs_fs_info *opts = fc->s_fs_info;
+	struct fs_parse_result result;
 	kuid_t uid;
 	kgid_t gid;
-	char *p;
-
-	opts->opts = 0;
-	opts->mode = TRACEFS_DEFAULT_MODE;
-
-	while ((p = strsep(&data, ",")) != NULL) {
-		if (!*p)
-			continue;
-
-		token = match_token(p, tokens, args);
-		switch (token) {
-		case Opt_uid:
-			if (match_int(&args[0], &option))
-				return -EINVAL;
-			uid = make_kuid(current_user_ns(), option);
-			if (!uid_valid(uid))
-				return -EINVAL;
-			opts->uid = uid;
-			break;
-		case Opt_gid:
-			if (match_int(&args[0], &option))
-				return -EINVAL;
-			gid = make_kgid(current_user_ns(), option);
-			if (!gid_valid(gid))
-				return -EINVAL;
-			opts->gid = gid;
-			break;
-		case Opt_mode:
-			if (match_octal(&args[0], &option))
-				return -EINVAL;
-			opts->mode = option & S_IALLUGO;
-			break;
-		/*
-		 * We might like to report bad mount options here;
-		 * but traditionally tracefs has ignored all mount options
-		 */
-		}
-
-		opts->opts |= BIT(token);
+	int opt;
+
+	opt = fs_parse(fc, tracefs_param_specs, param, &result);
+	if (opt < 0)
+		return opt;
+
+	switch (opt) {
+	case Opt_uid:
+		uid = make_kuid(current_user_ns(), result.uint_32);
+		if (!uid_valid(uid))
+			return invalf(fc, "Unknown uid");
+		opts->uid = uid;
+		break;
+	case Opt_gid:
+		gid = make_kgid(current_user_ns(), result.uint_32);
+		if (!gid_valid(gid))
+			return invalf(fc, "Unknown gid");
+		opts->gid = gid;
+		break;
+	case Opt_mode:
+		opts->mode = result.uint_32 & S_IALLUGO;
+		break;
+	/*
+	 * We might like to report bad mount options here;
+	 * but traditionally tracefs has ignored all mount options
+	 */
 	}
 
+	opts->opts |= BIT(opt);
+
 	return 0;
 }
 
@@ -312,7 +295,6 @@ static int tracefs_apply_options(struct super_block *sb, bool remount)
 {
 	struct tracefs_fs_info *fsi = sb->s_fs_info;
 	struct inode *inode = d_inode(sb->s_root);
-	struct tracefs_mount_opts *opts = &fsi->mount_opts;
 	umode_t tmp_mode;
 
 	/*
@@ -320,50 +302,46 @@ static int tracefs_apply_options(struct super_block *sb, bool remount)
 	 * options.
 	 */
 
-	if (!remount || opts->opts & BIT(Opt_mode)) {
+	if (!remount || fsi->opts & BIT(Opt_mode)) {
 		tmp_mode = READ_ONCE(inode->i_mode) & ~S_IALLUGO;
-		tmp_mode |= opts->mode;
+		tmp_mode |= fsi->mode;
 		WRITE_ONCE(inode->i_mode, tmp_mode);
 	}
 
-	if (!remount || opts->opts & BIT(Opt_uid))
-		inode->i_uid = opts->uid;
+	if (!remount || fsi->opts & BIT(Opt_uid))
+		inode->i_uid = fsi->uid;
 
-	if (!remount || opts->opts & BIT(Opt_gid))
-		inode->i_gid = opts->gid;
+	if (!remount || fsi->opts & BIT(Opt_gid))
+		inode->i_gid = fsi->gid;
 
 	return 0;
 }
 
-static int tracefs_remount(struct super_block *sb, int *flags, char *data)
+static int tracefs_reconfigure(struct fs_context *fc)
 {
-	int err;
-	struct tracefs_fs_info *fsi = sb->s_fs_info;
+	struct super_block *sb = fc->root->d_sb;
+	struct tracefs_fs_info *sb_opts = sb->s_fs_info;
+	struct tracefs_fs_info *new_opts = fc->s_fs_info;
 
 	sync_filesystem(sb);
-	err = tracefs_parse_options(data, &fsi->mount_opts);
-	if (err)
-		goto fail;
+	/* structure copy of new mount options to sb */
+	*sb_opts = *new_opts;
 
-	tracefs_apply_options(sb, true);
-
-fail:
-	return err;
+	return tracefs_apply_options(sb, true);
 }
 
 static int tracefs_show_options(struct seq_file *m, struct dentry *root)
 {
 	struct tracefs_fs_info *fsi = root->d_sb->s_fs_info;
-	struct tracefs_mount_opts *opts = &fsi->mount_opts;
 
-	if (!uid_eq(opts->uid, GLOBAL_ROOT_UID))
+	if (!uid_eq(fsi->uid, GLOBAL_ROOT_UID))
 		seq_printf(m, ",uid=%u",
-			   from_kuid_munged(&init_user_ns, opts->uid));
-	if (!gid_eq(opts->gid, GLOBAL_ROOT_GID))
+			   from_kuid_munged(&init_user_ns, fsi->uid));
+	if (!gid_eq(fsi->gid, GLOBAL_ROOT_GID))
 		seq_printf(m, ",gid=%u",
-			   from_kgid_munged(&init_user_ns, opts->gid));
-	if (opts->mode != TRACEFS_DEFAULT_MODE)
-		seq_printf(m, ",mode=%o", opts->mode);
+			   from_kgid_munged(&init_user_ns, fsi->gid));
+	if (fsi->mode != TRACEFS_DEFAULT_MODE)
+		seq_printf(m, ",mode=%o", fsi->mode);
 
 	return 0;
 }
@@ -373,7 +351,6 @@ static const struct super_operations tracefs_super_operations = {
 	.free_inode     = tracefs_free_inode,
 	.drop_inode     = generic_delete_inode,
 	.statfs		= simple_statfs,
-	.remount_fs	= tracefs_remount,
 	.show_options	= tracefs_show_options,
 };
 
@@ -403,26 +380,14 @@ static const struct dentry_operations tracefs_dentry_operations = {
 	.d_release = tracefs_d_release,
 };
 
-static int trace_fill_super(struct super_block *sb, void *data, int silent)
+static int tracefs_fill_super(struct super_block *sb, struct fs_context *fc)
 {
 	static const struct tree_descr trace_files[] = {{""}};
-	struct tracefs_fs_info *fsi;
 	int err;
 
-	fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
-	sb->s_fs_info = fsi;
-	if (!fsi) {
-		err = -ENOMEM;
-		goto fail;
-	}
-
-	err = tracefs_parse_options(data, &fsi->mount_opts);
-	if (err)
-		goto fail;
-
-	err  =  simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
+	err = simple_fill_super(sb, TRACEFS_MAGIC, trace_files);
 	if (err)
-		goto fail;
+		return err;
 
 	sb->s_op = &tracefs_super_operations;
 	sb->s_d_op = &tracefs_dentry_operations;
@@ -430,24 +395,45 @@ static int trace_fill_super(struct super_block *sb, void *data, int silent)
 	tracefs_apply_options(sb, false);
 
 	return 0;
+}
 
-fail:
-	kfree(fsi);
-	sb->s_fs_info = NULL;
-	return err;
+static int tracefs_get_tree(struct fs_context *fc)
+{
+	return get_tree_single(fc, tracefs_fill_super);
 }
 
-static struct dentry *trace_mount(struct file_system_type *fs_type,
-			int flags, const char *dev_name,
-			void *data)
+static void tracefs_free_fc(struct fs_context *fc)
 {
-	return mount_single(fs_type, flags, data, trace_fill_super);
+	kfree(fc->s_fs_info);
+}
+
+static const struct fs_context_operations tracefs_context_ops = {
+	.free		= tracefs_free_fc,
+	.parse_param	= tracefs_parse_param,
+	.get_tree	= tracefs_get_tree,
+	.reconfigure	= tracefs_reconfigure,
+};
+
+static int tracefs_init_fs_context(struct fs_context *fc)
+{
+	struct tracefs_fs_info *fsi;
+
+	fsi = kzalloc(sizeof(struct tracefs_fs_info), GFP_KERNEL);
+	if (!fsi)
+		return -ENOMEM;
+
+	fsi->mode = TRACEFS_DEFAULT_MODE;
+
+	fc->s_fs_info = fsi;
+	fc->ops = &tracefs_context_ops;
+	return 0;
 }
 
 static struct file_system_type trace_fs_type = {
 	.owner =	THIS_MODULE,
 	.name =		"tracefs",
-	.mount =	trace_mount,
+	.init_fs_context = tracefs_init_fs_context,
+	.parameters	= tracefs_param_specs,
 	.kill_sb =	kill_litter_super,
 };
 MODULE_ALIAS_FS("tracefs");