[PATCH] ANDROID: binderfs: add capabilities support

[Carlos Llamas <cmllamas@google.com>]

Provide userspace with a mechanism to discover binder driver
capabilities to refrain from using these unsupported features
in the first place. Note that older capabilities are assumed
to be supported and only new ones will be added.

Signed-off-by: Carlos Llamas <cmllamas@google.com>
---
 drivers/android/binderfs.c | 45 ++++++++++++++++++++++++++++++++++++++
 1 file changed, 45 insertions(+)

diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index e80ba93c62a9..f793887f6dc8 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -58,6 +58,10 @@ enum binderfs_stats_mode {
 	binderfs_stats_mode_global,
 };
 
+struct binder_capabilities {
+	bool oneway_spam;
+};
+
 static const struct constant_table binderfs_param_stats[] = {
 	{ "global", binderfs_stats_mode_global },
 	{}
@@ -69,6 +73,10 @@ static const struct fs_parameter_spec binderfs_fs_parameters[] = {
 	{}
 };
 
+static struct binder_capabilities binder_caps = {
+	.oneway_spam = true,
+};
+
 static inline struct binderfs_info *BINDERFS_SB(const struct super_block *sb)
 {
 	return sb->s_fs_info;
@@ -583,6 +591,39 @@ static struct dentry *binderfs_create_dir(struct dentry *parent,
 	return dentry;
 }
 
+static int binder_caps_show(struct seq_file *m, void *unused)
+{
+	bool *cap = m->private;
+
+	seq_printf(m, "%d\n", *cap);
+
+	return 0;
+}
+DEFINE_SHOW_ATTRIBUTE(binder_caps);
+
+static int init_binder_caps(struct super_block *sb)
+{
+	struct dentry *dentry, *root;
+	int ret = 0;
+
+	root = binderfs_create_dir(sb->s_root, "caps");
+	if (IS_ERR(root)) {
+		ret = PTR_ERR(root);
+		goto out;
+	}
+
+	dentry = binderfs_create_file(root, "oneway_spam",
+				      &binder_caps_fops,
+				      &binder_caps.oneway_spam);
+	if (IS_ERR(dentry)) {
+		ret = PTR_ERR(dentry);
+		goto out;
+	}
+
+out:
+	return ret;
+}
+
 static int init_binder_logs(struct super_block *sb)
 {
 	struct dentry *binder_logs_root_dir, *dentry, *proc_log_dir;
@@ -723,6 +764,10 @@ static int binderfs_fill_super(struct super_block *sb, struct fs_context *fc)
 			name++;
 	}
 
+	ret = init_binder_caps(sb);
+	if (ret)
+		return ret;
+
 	if (info->mount_opts.stats_mode == binderfs_stats_mode_global)
 		return init_binder_logs(sb);
 
-- 
2.32.0.93.g670b81a890-goog