[PATCH v2 3/4] firewire: core: Prevent device_find_child() from modifying caller's match data

[Zijun Hu <zijun_hu@icloud.com>]

From: Zijun Hu <quic_zijuhu@quicinc.com>

To prepare for constifying the following old driver core API:

struct device *device_find_child(struct device *dev, void *data,
		int (*match)(struct device *dev, void *data));
to new:
struct device *device_find_child(struct device *dev, const void *data,
		int (*match)(struct device *dev, const void *data));

The new API does not allow its match function (*match)() to modify
caller's match data @*data, but lookup_existing_device() as the old
API's match function indeed modifies relevant match data, so it is not
suitable for the new API any more, fixed by implementing a equivalent
fw_device_find_child() instead of the old API usage.

Signed-off-by: Zijun Hu <quic_zijuhu@quicinc.com>
---
 drivers/firewire/core-device.c | 37 +++++++++++++++++++++++++++++++++++--
 1 file changed, 35 insertions(+), 2 deletions(-)

diff --git a/drivers/firewire/core-device.c b/drivers/firewire/core-device.c
index 00e9a13e6c45..7fbccb113d54 100644
--- a/drivers/firewire/core-device.c
+++ b/drivers/firewire/core-device.c
@@ -33,6 +33,39 @@
 
 #define ROOT_DIR_OFFSET	5
 
+struct fw_dfc_data {
+	int (*match)(struct device *dev, void *data);
+	void *data;
+	struct device *target_device;
+};
+
+static int fw_dfc_match_modify(struct device *dev, void *data)
+{
+	struct fw_dfc_data *dfc_data =  data;
+	int res;
+
+	res = dfc_data->match(dev, dfc_data->data);
+	if (res && get_device(dev)) {
+		dfc_data->target_device = dev;
+		return res;
+	}
+
+	return 0;
+}
+
+/*
+ * I have the same function as device_find_child() but allow to modify
+ * caller's match data @*data.
+ */
+static struct device *fw_device_find_child(struct device *parent, void *data,
+					   int (*match)(struct device *dev, void *data))
+{
+	struct fw_dfc_data dfc_data = {match, data, NULL};
+
+	device_for_each_child(parent, &dfc_data, fw_dfc_match_modify);
+	return dfc_data.target_device;
+}
+
 void fw_csr_iterator_init(struct fw_csr_iterator *ci, const u32 *p)
 {
 	ci->p = p + 1;
@@ -1087,8 +1120,8 @@ static void fw_device_init(struct work_struct *work)
 		return;
 	}
 
-	revived_dev = device_find_child(card->device,
-					device, lookup_existing_device);
+	revived_dev = fw_device_find_child(card->device, device,
+					   lookup_existing_device);
 	if (revived_dev) {
 		put_device(revived_dev);
 		fw_device_release(&device->device);

-- 
2.34.1