all: Allow backend to provide a better get_config_descriptor_by_value

Our core get_config_descriptor_by_value is not exactly pretty nor efficient,
allow the backends to provide something better.

Note that the callback signature differs from get_config_descriptor in that
backend owned memory gets returned. This saves a needless malloc + memcpy +
free. If this turns out to be a problem for some backends we can always
change things to work like get_config_descriptor.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>

7 files changed, 39 insertions, 9 deletions

diff --git a/libusb/descriptor.c b/libusb/descriptor.c
index 5fb96ea..44d93ee 100644
--- a/libusb/descriptor.c
+++ b/libusb/descriptor.c
@@ -678,8 +678,18 @@ int usbi_get_config_index_by_value(struct libusb_device *dev,
 int API_EXPORTED libusb_get_config_descriptor_by_value(libusb_device *dev,
 	uint8_t bConfigurationValue, struct libusb_config_descriptor **config)
 {
-	int idx;
-	int r = usbi_get_config_index_by_value(dev, bConfigurationValue, &idx);
+	int r, idx, host_endian;
+	unsigned char *buf = NULL;
+
+	if (usbi_backend->get_config_descriptor_by_value) {
+		r = usbi_backend->get_config_descriptor_by_value(dev,
+			bConfigurationValue, &buf, &host_endian);
+		if (r < 0)
+			return r;
+		return raw_desc_to_config(dev->ctx, buf, r, host_endian, config);
+	}
+
+	r = usbi_get_config_index_by_value(dev, bConfigurationValue, &idx);
 	if (r < 0)
 		return r;
 	else if (idx == -1)
diff --git a/libusb/libusbi.h b/libusb/libusbi.h
index bf240e8..090ac5b 100644
--- a/libusb/libusbi.h
+++ b/libusb/libusbi.h
@@ -665,6 +665,22 @@ struct usbi_os_backend {
 		uint8_t config_index, unsigned char *buffer, size_t len,
 		int *host_endian);
 
+	/* Like get_config_descriptor but then by bConfigurationValue instead
+	 * of by index.
+	 *
+	 * Optional, if not present the core will call get_config_descriptor
+	 * for all configs until it finds the desired bConfigurationValue.
+	 *
+	 * Returns a pointer to the raw-descriptor in *buffer, this memory
+	 * is valid as long as device is valid.
+	 *
+	 * Returns the length of the returned raw-descriptor on success,
+	 * or a LIBUSB_ERROR code on failure.
+	 */
+	int (*get_config_descriptor_by_value)(struct libusb_device *device,
+		uint8_t bConfigurationValue, unsigned char **buffer,
+		int *host_endian);
+
 	/* Get the bConfigurationValue for the active configuration for a device.
 	 * Optional. This should only be implemented if you can retrieve it from
 	 * cache (don't generate I/O).
diff --git a/libusb/os/linux_usbfs.c b/libusb/os/linux_usbfs.c
index 280e312..57ab80c 100644
--- a/libusb/os/linux_usbfs.c
+++ b/libusb/os/linux_usbfs.c
@@ -701,8 +701,8 @@ static int seek_to_next_config(struct libusb_context *ctx,
 	}
 }
 
-static int get_config_descriptor_by_value(struct libusb_device *dev,
-	unsigned char **buffer, uint8_t value)
+static int op_get_config_descriptor_by_value(struct libusb_device *dev,
+	uint8_t value, unsigned char **buffer, int *host_endian)
 {
 	struct libusb_context *ctx = DEVICE_CTX(dev);
 	struct linux_device_priv *priv = _device_priv(dev);
@@ -711,6 +711,8 @@ static int get_config_descriptor_by_value(struct libusb_device *dev,
 	struct libusb_config_descriptor *config;
 
 	*buffer = NULL;
+	/* Unlike the device desc. config descs. are always in raw format */
+	*host_endian = 0;
 
 	/* Skip device header */
 	descriptors += DEVICE_DESC_LENGTH;
@@ -737,9 +739,6 @@ static int op_get_active_config_descriptor(struct libusb_device *dev,
 	int r, config;
 	unsigned char *config_desc;
 
-	/* Unlike the device desc. config descs. are always in raw format */
-	*host_endian = 0;
-
 	if (sysfs_can_relate_devices) {
 		r = sysfs_get_active_config(dev, &config);
 		if (r < 0)
@@ -752,7 +751,8 @@ static int op_get_active_config_descriptor(struct libusb_device *dev,
 	if (config == -1)
 		return LIBUSB_ERROR_NOT_FOUND;
 
-	r = get_config_descriptor_by_value(dev, &config_desc, config);
+	r = op_get_config_descriptor_by_value(dev, config, &config_desc,
+					      host_endian);
 	if (r < 0)
 		return r;
 
@@ -2458,6 +2458,7 @@ const struct usbi_os_backend linux_usbfs_backend = {
 	.get_device_descriptor = op_get_device_descriptor,
 	.get_active_config_descriptor = op_get_active_config_descriptor,
 	.get_config_descriptor = op_get_config_descriptor,
+	.get_config_descriptor_by_value = op_get_config_descriptor_by_value,
 
 	.open = op_open,
 	.close = op_close,
diff --git a/libusb/os/openbsd_usb.c b/libusb/os/openbsd_usb.c
index 06aaff4..e1c91f4 100644
--- a/libusb/os/openbsd_usb.c
+++ b/libusb/os/openbsd_usb.c
@@ -99,6 +99,7 @@ const struct usbi_os_backend openbsd_backend = {
 	obsd_get_device_descriptor,
 	obsd_get_active_config_descriptor,
 	obsd_get_config_descriptor,
+	NULL,				/* get_config_descriptor_by_value() */
 
 	obsd_get_configuration,
 	obsd_set_configuration,
diff --git a/libusb/os/wince_usb.c b/libusb/os/wince_usb.c
index 2e6eedd..f1f64ac 100644
--- a/libusb/os/wince_usb.c
+++ b/libusb/os/wince_usb.c
@@ -984,6 +984,7 @@ const struct usbi_os_backend wince_backend = {
         wince_get_device_descriptor,
         wince_get_active_config_descriptor,
         wince_get_config_descriptor,
+	NULL,				/* get_config_descriptor_by_value() */
 
         wince_get_configuration,
         wince_set_configuration,
diff --git a/libusb/os/windows_usb.c b/libusb/os/windows_usb.c
index 061a0f8..3eb5585 100644
--- a/libusb/os/windows_usb.c
+++ b/libusb/os/windows_usb.c
@@ -2275,6 +2275,7 @@ const struct usbi_os_backend windows_backend = {
 	windows_get_device_descriptor,
 	windows_get_active_config_descriptor,
 	windows_get_config_descriptor,
+	NULL,				/* get_config_descriptor_by_value() */
 
 	windows_get_configuration,
 	windows_set_configuration,
diff --git a/libusb/version_nano.h b/libusb/version_nano.h
index 0d49847..c29c8ff 100644
--- a/libusb/version_nano.h
+++ b/libusb/version_nano.h
@@ -1 +1 @@
-#define LIBUSB_NANO 10713
+#define LIBUSB_NANO 10714