[PATCH v3 1/2] binder: Add default binder devices through binderfs when configured

[Hridya Valsaraju <hridya@google.com>]

Currently, since each binderfs instance needs its own
private binder devices, every time a binderfs instance is
mounted, all the default binder devices need to be created
via the BINDER_CTL_ADD IOCTL. This patch aims to
add a solution to automatically create the default binder
devices for each binderfs instance that gets mounted.
To achieve this goal, when CONFIG_ANDROID_BINDERFS is set,
the default binder devices specified by CONFIG_ANDROID_BINDER_DEVICES
are created in each binderfs instance instead of global devices
being created by the binder driver.

Co-developed-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Hridya Valsaraju <hridya@google.com>
---

Changes in v2:
- Updated commit message as per Greg Kroah-Hartman.
- Removed new module parameter creation as per Greg
  Kroah-Hartman/Christian Brauner.
- Refactored device name length check into a new patch as per Greg Kroah-Hartman.

Changes in v3:
-Removed unnecessary empty lines as per Dan Carpenter.

 drivers/android/binder.c          |  5 +++--
 drivers/android/binder_internal.h |  2 ++
 drivers/android/binderfs.c        | 23 ++++++++++++++++++++---
 3 files changed, 25 insertions(+), 5 deletions(-)

diff --git a/drivers/android/binder.c b/drivers/android/binder.c
index 466b6a7f8ab7..ca6b21a53321 100644
--- a/drivers/android/binder.c
+++ b/drivers/android/binder.c
@@ -123,7 +123,7 @@ static uint32_t binder_debug_mask = BINDER_DEBUG_USER_ERROR |
 	BINDER_DEBUG_FAILED_TRANSACTION | BINDER_DEBUG_DEAD_TRANSACTION;
 module_param_named(debug_mask, binder_debug_mask, uint, 0644);
 
-static char *binder_devices_param = CONFIG_ANDROID_BINDER_DEVICES;
+char *binder_devices_param = CONFIG_ANDROID_BINDER_DEVICES;
 module_param_named(devices, binder_devices_param, charp, 0444);
 
 static DECLARE_WAIT_QUEUE_HEAD(binder_user_error_wait);
@@ -6279,7 +6279,8 @@ static int __init binder_init(void)
 				    &transaction_log_fops);
 	}
 
-	if (strcmp(binder_devices_param, "") != 0) {
+	if (!IS_ENABLED(CONFIG_ANDROID_BINDERFS) &&
+	    strcmp(binder_devices_param, "") != 0) {
 		/*
 		* Copy the module_parameter string, because we don't want to
 		* tokenize it in-place.
diff --git a/drivers/android/binder_internal.h b/drivers/android/binder_internal.h
index 045b3e42d98b..fe8c745dc8e0 100644
--- a/drivers/android/binder_internal.h
+++ b/drivers/android/binder_internal.h
@@ -37,6 +37,8 @@ struct binder_device {
 
 extern const struct file_operations binder_fops;
 
+extern char *binder_devices_param;
+
 #ifdef CONFIG_ANDROID_BINDERFS
 extern bool is_binderfs_device(const struct inode *inode);
 #else
diff --git a/drivers/android/binderfs.c b/drivers/android/binderfs.c
index e773f45d19d9..aee46dd1be91 100644
--- a/drivers/android/binderfs.c
+++ b/drivers/android/binderfs.c
@@ -186,8 +186,7 @@ static int binderfs_binder_device_create(struct inode *ref_inode,
 	req->major = MAJOR(binderfs_dev);
 	req->minor = minor;
 
-	ret = copy_to_user(userp, req, sizeof(*req));
-	if (ret) {
+	if (userp && copy_to_user(userp, req, sizeof(*req))) {
 		ret = -EFAULT;
 		goto err;
 	}
@@ -467,6 +466,9 @@ static int binderfs_fill_super(struct super_block *sb, void *data, int silent)
 	int ret;
 	struct binderfs_info *info;
 	struct inode *inode = NULL;
+	struct binderfs_device device_info = { 0 };
+	const char *name;
+	size_t len;
 
 	sb->s_blocksize = PAGE_SIZE;
 	sb->s_blocksize_bits = PAGE_SHIFT;
@@ -521,7 +523,22 @@ static int binderfs_fill_super(struct super_block *sb, void *data, int silent)
 	if (!sb->s_root)
 		return -ENOMEM;
 
-	return binderfs_binder_ctl_create(sb);
+	ret = binderfs_binder_ctl_create(sb);
+	if (ret)
+		return ret;
+
+	name = binder_devices_param;
+	for (len = strcspn(name, ","); len > 0; len = strcspn(name, ",")) {
+		strscpy(device_info.name, name, len + 1);
+		ret = binderfs_binder_device_create(inode, NULL, &device_info);
+		if (ret)
+			return ret;
+		name += len;
+		if (*name == ',')
+			name++;
+	}
+
+	return 0;
 }
 
 static struct dentry *binderfs_mount(struct file_system_type *fs_type,
-- 
2.22.0.770.g0f2c4a37fd-goog