ANDROID: sdcardfs: Add option to not link obb

Add mount option unshared_obb to not link the obb
folders of multiple users together.

Bug: 27915347
Test: mount with option. Check if altering one obb
      alters the other
Signed-off-by: Daniel Rosenberg <drosen@google.com>

Change-Id: I3956e06bd0a222b0bbb2768c9a8a8372ada85e1e

3 files changed, 12 insertions, 2 deletions

diff --git a/fs/sdcardfs/derived_perm.c b/fs/sdcardfs/derived_perm.c
index 7311c75f8..9f2e431c7 100755
--- a/fs/sdcardfs/derived_perm.c
+++ b/fs/sdcardfs/derived_perm.c
@@ -356,7 +356,8 @@ int need_graft_path(struct dentry *dentry)
 	struct sdcardfs_sb_info *sbi = SDCARDFS_SB(dentry->d_sb);
 	struct qstr obb = QSTR_LITERAL("obb");
 
-	if (parent_info->data->perm == PERM_ANDROID &&
+	if (!sbi->options.unshared_obb &&
+			parent_info->data->perm == PERM_ANDROID &&
 			qstr_case_eq(&dentry->d_name, &obb)) {
 
 		/* /Android/obb is the base obbpath of DERIVED_UNIFIED */
diff --git a/fs/sdcardfs/main.c b/fs/sdcardfs/main.c
index 8e12a7dda..280ad597f 100755
--- a/fs/sdcardfs/main.c
+++ b/fs/sdcardfs/main.c
@@ -35,6 +35,7 @@ enum {
 	Opt_gid_derivation,
 	Opt_default_normal,
 	Opt_nocache,
+	Opt_unshared_obb,
 	Opt_err,
 };
 
@@ -48,6 +49,7 @@ static const match_table_t sdcardfs_tokens = {
 	{Opt_multiuser, "multiuser"},
 	{Opt_gid_derivation, "derive_gid"},
 	{Opt_default_normal, "default_normal"},
+	{Opt_unshared_obb, "unshared_obb"},
 	{Opt_reserved_mb, "reserved_mb=%u"},
 	{Opt_nocache, "nocache"},
 	{Opt_err, NULL}
@@ -133,6 +135,9 @@ static int parse_options(struct super_block *sb, char *options, int silent,
 		case Opt_nocache:
 			opts->nocache = true;
 			break;
+		case Opt_unshared_obb:
+			opts->unshared_obb = true;
+			break;
 		/* unknown option */
 		default:
 			if (!silent)
@@ -186,13 +191,16 @@ int parse_options_remount(struct super_block *sb, char *options, int silent,
 				return 0;
 			vfsopts->mask = option;
 			break;
+		case Opt_unshared_obb:
 		case Opt_default_normal:
 		case Opt_multiuser:
 		case Opt_userid:
 		case Opt_fsuid:
 		case Opt_fsgid:
 		case Opt_reserved_mb:
-			pr_warn("Option \"%s\" can't be changed during remount\n", p);
+		case Opt_gid_derivation:
+			if (!silent)
+				pr_warn("Option \"%s\" can't be changed during remount\n", p);
 			break;
 		/* unknown option */
 		default:
diff --git a/fs/sdcardfs/sdcardfs.h b/fs/sdcardfs/sdcardfs.h
index 0d94d56c7..6b18547fc 100755
--- a/fs/sdcardfs/sdcardfs.h
+++ b/fs/sdcardfs/sdcardfs.h
@@ -195,6 +195,7 @@ struct sdcardfs_mount_options {
 	bool multiuser;
 	bool gid_derivation;
 	bool default_normal;
+	bool unshared_obb;
 	unsigned int reserved_mb;
 	bool nocache;
 };