Re: [PATCH 14/33] vfs: Implement a filesystem superblock creation/configuration context [ver #11]

[David Howells <dhowells@redhat.com>]

I think I need to include something like the attached change in this patch.
Changes also need to be made to proc and cgroup.

David
---
commit 1a336480a0f664b3e1988a581bccd4fa10d98764
Author: David Howells <dhowells@redhat.com>
Date:   Tue Sep 18 17:25:23 2018 +0100

    fix remount

diff --git a/fs/fs_context.c b/fs/fs_context.c
index a82679441031..1f36b72e3ee9 100644
--- a/fs/fs_context.c
+++ b/fs/fs_context.c
@@ -42,8 +42,6 @@ struct legacy_fs_context {
 	enum legacy_fs_param	param_type;
 };
 
-static int legacy_init_fs_context(struct fs_context *fc, struct dentry *dentry);
-
 static const struct constant_table common_set_sb_flag[] = {
 	{ "dirsync",	SB_DIRSYNC },
 	{ "lazytime",	SB_LAZYTIME },
@@ -293,7 +291,6 @@ struct fs_context *vfs_new_fs_context(struct file_system_type *fs_type,
 		break;
 	}
 
-
 	/* TODO: Make all filesystems support this unconditionally */
 	init_fs_context = fc->fs_type->init_fs_context;
 	if (!init_fs_context)
@@ -662,12 +659,20 @@ const struct fs_context_operations legacy_fs_context_ops = {
  * Initialise a legacy context for a filesystem that doesn't support
  * fs_context.
  */
-static int legacy_init_fs_context(struct fs_context *fc, struct dentry *dentry)
+int legacy_init_fs_context(struct fs_context *fc, struct dentry *dentry)
 {
+	switch (fc->purpose) {
+	default:
+		fc->fs_private = kzalloc(sizeof(struct legacy_fs_context),
+					 GFP_KERNEL);
+		if (!fc->fs_private)
+			return -ENOMEM;
+		break;
 
-	fc->fs_private = kzalloc(sizeof(struct legacy_fs_context), GFP_KERNEL);
-	if (!fc->fs_private)
-		return -ENOMEM;
+	case FS_CONTEXT_FOR_UMOUNT:
+	case FS_CONTEXT_FOR_EMERGENCY_RO:
+		break;
+	}
 
 	fc->ops = &legacy_fs_context_ops;
 	return 0;
diff --git a/fs/internal.h b/fs/internal.h
index d25cb82af69d..fc2da60abbcd 100644
--- a/fs/internal.h
+++ b/fs/internal.h
@@ -55,6 +55,7 @@ extern void __init chrdev_init(void);
  * fs_context.c
  */
 extern const struct fs_context_operations legacy_fs_context_ops;
+extern int legacy_init_fs_context(struct fs_context *fc, struct dentry *dentry);
 
 /*
  * fsopen.c
diff --git a/fs/namespace.c b/fs/namespace.c
index ddb2c3b88cd6..86b60566fcdf 100644
--- a/fs/namespace.c
+++ b/fs/namespace.c
@@ -1429,9 +1429,19 @@ static int do_umount_root(struct super_block *sb)
 	};
 
 	down_write(&sb->s_umount);
-	if (!sb_rdonly(sb))
-		/* Might want to call ->init_fs_context(). */
-		ret = reconfigure_super(&fc);
+	if (!sb_rdonly(sb)) {
+		int ret;
+
+		if (fc.fs_type->init_fs_context)
+			ret = fc.fs_type->init_fs_context(&fc, NULL);
+		else
+			ret = legacy_init_fs_context(&fc, NULL);
+
+		if (ret == 0) {
+			ret = reconfigure_super(&fc);
+			fc.ops->free(&fc);
+		}
+	}
 	up_write(&sb->s_umount);
 	return ret;
 }
@@ -2396,7 +2406,7 @@ static int do_remount(struct path *path, int ms_flags, int sb_flags,
 
 	err = security_fs_context_validate(fc);
 	if (err)
-		return err;
+		goto err_fc;
 
 	down_write(&sb->s_umount);
 	err = -EPERM;
diff --git a/fs/super.c b/fs/super.c
index e00b03249bfa..df8c4cebd000 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -1026,12 +1026,20 @@ static void do_emergency_remount_callback(struct super_block *sb)
 
 	down_write(&sb->s_umount);
 	if (sb->s_root && sb->s_bdev && (sb->s_flags & SB_BORN) &&
-	    !sb_rdonly(sb))
-		/* Might want to call ->init_fs_context(). */
+	    !sb_rdonly(sb)) {
+		int ret;
+
+		if (fc.fs_type->init_fs_context)
+			ret = fc.fs_type->init_fs_context(&fc, NULL);
+		else
+			ret = legacy_init_fs_context(&fc, NULL);
+
 		/*
 		 * What lock protects sb->s_flags??
 		 */
-		reconfigure_super(&fc);
+		if (ret == 0)
+			reconfigure_super(&fc);
+	}
 	up_write(&sb->s_umount);
 }