From 4f2a365e20831076816b8672735118f654ccfcd8 Mon Sep 17 00:00:00 2001

From: Michael Drake <michael.drake@codethink.co.uk>

Date: Thu, 7 Jun 2018 12:41:16 +0100

Subject: [PATCH 7/9] lsusb: Add support for descriptor extensions.

These allow descriptors with common fields at the start, one of

which common fields specifies a field whos value determines which

of a set of descriptor extensions should be used to render the

remainder of the descriptor.

Signed-off-by: Michael Drake <michael.drake@codethink.co.uk>

---

 desc-defs.c | 11 ++++++++++-

 desc-defs.h | 39 ++++++++++++++++++++++++++++++++++++++-

 desc-dump.c | 52 +++++++++++++++++++++++++++++++++++++++++++++-------

 3 files changed, 93 insertions(+), 9 deletions(-)

diff --git a/desc-defs.c b/desc-defs.c

index 4c374e0..60cc603 100644

--- a/desc-defs.c

+++ b/desc-defs.c

@@ -2,7 +2,7 @@

 /*

  * USB descriptor definitions

  *

- * Copyright (C) 2017 Michael Drake <michael.drake@codethink.co.uk>

+ * Copyright (C) 2017-2018 Michael Drake <michael.drake@codethink.co.uk>

  */

 #include "config.h"

@@ -441,6 +441,15 @@ static const struct desc desc_audio_2_ac_processing_unit[] = {

 	{ .field = NULL }

 };

+/**

+ * Undefined descriptor

+ *

+ * Ensures remaining data is dumped as garbage at end of descriptor.

+ */

+const struct desc desc_undefined[] = {

+	{ .field = NULL }

+};

+

 /** UAC3: 4.5.2.10 Processing Unit Descriptor; Table 4-38. */

 static const struct desc desc_audio_3_ac_processing_unit[] = {

 	{ .field = "bUnitID",             .size = 1, .type = DESC_NUMBER },

diff --git a/desc-defs.h b/desc-defs.h

index 99d5caa..aa695e4 100644

--- a/desc-defs.h

+++ b/desc-defs.h

@@ -2,7 +2,7 @@

 /*

  * USB descriptor definitions

  *

- * Copyright (C) 2017 Michael Drake <michael.drake@codethink.co.uk>

+ * Copyright (C) 2017-2018 Michael Drake <michael.drake@codethink.co.uk>

  */

 #ifndef _DESC_DEFS_H

@@ -33,6 +33,7 @@ enum desc_type {

 	DESC_TERMINAL_STR,   /**< Audio terminal string. */

 	DESC_BITMAP_STRINGS, /**< Bitfield with string per bit. */

 	DESC_NUMBER_STRINGS, /**< Use for enum-style value to string. */

+	DESC_EXTENSION,      /**< Various possible descriptor extensions. */

 	DESC_SNOWFLAKE,  /**< Value with custom annotation callback function. */

 };

@@ -95,6 +96,39 @@ struct desc {

 		 * Must be a '\0' terminated string.

 		 */

 		const char *number_postfix;

+		/**

+		 * Corresponds to type DESC_EXTENSION.

+		 *

+		 * This allows the value of this field to be processed by

+		 * another descriptor definition.  The definition used to

+		 * process the value of this field can be controlled by

+		 * the value of another field.

+		 */

+		struct {

+			/**

+			 * Name of field specifying descriptor type to select.

+			 */

+			const char *type_field;

+			/**

+			 * Array of descriptor definitions and their

+			 * associated types values.  Array must be terminated

+			 * by entry with NULL `desc` member.

+			 */

+			const struct desc_ext {

+				/**

+				 * Array of descriptor field definitions.

+				 * Terminated by entry with NULL `field` member.

+				 */

+				const struct desc *desc;

+				/**

+				 * Type value for this descriptor definition.

+				 * If it matches the type read from the

+				 * field `type_field`, then this descriptor

+				 * definition will be used to decode this value.

+				 */

+				unsigned int type;

+			} *d;

+		} extension;

 		/**

 		 * Corresponds to type DESC_SNOWFLAKE.

 		 *

@@ -116,6 +150,9 @@ struct desc {

 /* ---------------------------------------------------------------------- */

+/* Undefined descriptor */

+extern const struct desc desc_undefined[];

+

 /* Audio Control (AC) descriptor definitions */

 extern const struct desc * const desc_audio_ac_header[3];

 extern const struct desc * const desc_audio_ac_effect_unit[3];

diff --git a/desc-dump.c b/desc-dump.c

index 2f92768..19d2cc7 100644

--- a/desc-dump.c

+++ b/desc-dump.c

@@ -211,8 +211,10 @@ static void number_renderer(

  *

  * \param[in] dev           LibUSB device handle.

  * \param[in] current       Descriptor definition field to render.

- * \param[in] current_size  Descriptor definition field to render.

+ * \param[in] current_size  Size of value to render.

  * \param[in] buf           Byte array containing the descriptor date to dump.

+ * \param[in] buf_len       Byte length of `buf`.

+ * \param[in] desc          First field in the descriptor definition.

  * \param[in] indent        Current indent level.

  * \param[in] offset        Offset to current value in `buf`.

  */

@@ -221,6 +223,8 @@ static void value_renderer(

 		const struct desc *current,

 		unsigned int current_size,

 		const unsigned char *buf,

+		unsigned int buf_len,

+		const struct desc *desc,

 		unsigned int indent,

 		size_t offset)

 {

@@ -312,6 +316,31 @@ static void value_renderer(

 		printf(" %s\n", names_audioterminal(

 				get_n_bytes_as_ull(buf, offset, current_size)));

 		break;

+	case DESC_EXTENSION: {

+		unsigned int type = get_value_from_field(buf, desc,

+				current->extension.type_field);

+		const struct desc *ext_desc;

+		const struct desc_ext *ext;

+

+		/* Lookup the extention descriptor definitions to use, */

+		for (ext = current->extension.d; ext->desc != NULL; ext++) {

+			if (ext->type == type) {

+				ext_desc = ext->desc;

+				break;

+			}

+		}

+

+		/* If the type didn't match a known type, use the

+		 * undefined descriptor. */

+		if (ext->desc == NULL) {

+			ext_desc = desc_undefined;

+		}

+

+		desc_dump(dev, ext_desc, buf + offset,

+				buf_len - offset, indent);

+

+		break;

+	}

 	case DESC_SNOWFLAKE:

 		number_renderer(buf, size_chars, offset, current_size);

 		current->snowflake(

@@ -537,14 +566,23 @@ void desc_dump(

 			}

 			/* Dump the field name */

-			field_render(entry, entries, field_len,

-					current, indent);

+			if (current->type != DESC_EXTENSION) {

+				field_render(entry, entries, field_len,

+						current, indent);

+			}

 			/* Dump the value */

-			value_renderer(dev, current, current_size, buf,

-					indent, offset);

-			/* Advance offset in buffer */

-			offset += current_size;

+			value_renderer(dev, current, current_size, buf, buf_len,

+					desc, indent, offset);

+

+			if (current->type == DESC_EXTENSION) {

+				/* A desc extension consumes all remaining

+				 * value buffer. */

+				offset = buf_len;

+			} else {

+				/* Advance offset in buffer */

+				offset += current_size;

+			}

 		}

 	}

-- 

2.14.4