core: Introduce accessor functions for structure private data

The backend private data for the internal library structures has been
accessed through a zero-length os_priv array of type unsigned char.
This approach had two particular disadvantages:

  1) A special attribute was needed on the 'os_priv' member to ensure
     that the field was properly aligned to a natural pointer alignment.
     The support needed for this is not available in every compiler.

  2) Each access to the private data areas required an explicit cast
     from unsigned char to the type required by the backend.

This change reworks the way the private data is accessed by the
backends. New accessor functions return the private data as a void
pointer type, removing the need for an explicit cast (except for Haiku,
which is C++). The special alignment attribute trickery is also replaced
by simple pointer arithmetic.

Signed-off-by: Chris Dickens <christopher.a.dickens@gmail.com>

1 files changed, 33 insertions, 33 deletions

diff --git a/libusb/libusbi.h b/libusb/libusbi.h
index 57333d8..c60b201 100644
--- a/libusb/libusbi.h
+++ b/libusb/libusbi.h
@@ -68,20 +68,6 @@
 #define PTR_ALIGN(v) \
 	(((v) + (sizeof(void *) - 1)) & ~(sizeof(void *) - 1))
 
-/* Attribute to ensure that a structure member is aligned to a natural
- * pointer alignment. Used for os_priv member. */
-#if defined(_MSC_VER)
-#if defined(_WIN64)
-#define PTR_ALIGNED __declspec(align(8))
-#else
-#define PTR_ALIGNED __declspec(align(4))
-#endif
-#elif defined(__GNUC__) && (__GNUC__ >= 3)
-#define PTR_ALIGNED __attribute__((aligned(sizeof(void *))))
-#else
-#define PTR_ALIGNED
-#endif
-
 /* Internal abstraction for poll */
 #if defined(POLL_POSIX)
 #include "os/poll_posix.h"
@@ -367,8 +353,6 @@ struct libusb_context {
 #endif
 
 	struct list_head list;
-
-	PTR_ALIGNED unsigned char os_priv[ZERO_SIZED_ARRAY];
 };
 
 extern struct libusb_context *usbi_default_context;
@@ -444,8 +428,6 @@ struct libusb_device {
 
 	struct libusb_device_descriptor device_descriptor;
 	int attached;
-
-	PTR_ALIGNED unsigned char os_priv[ZERO_SIZED_ARRAY];
 };
 
 struct libusb_device_handle {
@@ -456,8 +438,6 @@ struct libusb_device_handle {
 	struct list_head list;
 	struct libusb_device *dev;
 	int auto_detach_kernel_driver;
-
-	PTR_ALIGNED unsigned char os_priv[ZERO_SIZED_ARRAY];
 };
 
 enum {
@@ -496,7 +476,7 @@ struct usbi_transfer {
 	 * always take the flying_transfers_lock first */
 	usbi_mutex_t lock;
 
-	void *os_priv;
+	void *priv;
 
 	struct libusb_transfer libusb_transfer;
 };
@@ -528,11 +508,6 @@ enum usbi_transfer_timeout_flags {
 #define LIBUSB_TRANSFER_TO_USBI_TRANSFER(transfer)			\
 	container_of(transfer, struct usbi_transfer, libusb_transfer)
 
-static inline void *usbi_transfer_get_os_priv(struct usbi_transfer *itransfer)
-{
-	return itransfer->os_priv;
-}
-
 /* All standard descriptors have these 2 fields in common */
 struct usb_descriptor_header {
 	uint8_t bLength;
@@ -578,6 +553,28 @@ struct usbi_pollfd {
 int usbi_add_pollfd(struct libusb_context *ctx, int fd, short events);
 void usbi_remove_pollfd(struct libusb_context *ctx, int fd);
 
+/* accessor functions for structure private data */
+
+static inline void *usbi_get_context_priv(struct libusb_context *ctx)
+{
+	return (unsigned char *)ctx + PTR_ALIGN(sizeof(*ctx));
+}
+
+static inline void *usbi_get_device_priv(struct libusb_device *dev)
+{
+	return (unsigned char *)dev + PTR_ALIGN(sizeof(*dev));
+}
+
+static inline void *usbi_get_device_handle_priv(struct libusb_device_handle *dev_handle)
+{
+	return (unsigned char *)dev_handle + PTR_ALIGN(sizeof(*dev_handle));
+}
+
+static inline void *usbi_get_transfer_priv(struct usbi_transfer *itransfer)
+{
+	return itransfer->priv;
+}
+
 /* device discovery */
 
 /* we traverse usbfs without knowing how many devices we are going to find.
@@ -1158,23 +1155,26 @@ struct usbi_os_backend {
 	int (*clock_gettime)(int clkid, struct timespec *tp);
 
 	/* Number of bytes to reserve for per-context private backend data.
-	 * This private data area is accessible through the "os_priv" field of
-	 * struct libusb_context. */
+	 * This private data area is accessible by calling
+	 * usbi_get_context_priv() on the libusb_context instance.
+	 */
 	size_t context_priv_size;
 
 	/* Number of bytes to reserve for per-device private backend data.
-	 * This private data area is accessible through the "os_priv" field of
-	 * struct libusb_device. */
+	 * This private data area is accessible by calling
+	 * usbi_get_device_priv() on the libusb_device instance.
+	 */
 	size_t device_priv_size;
 
 	/* Number of bytes to reserve for per-handle private backend data.
-	 * This private data area is accessible through the "os_priv" field of
-	 * struct libusb_device_handle. */
+	 * This private data area is accessible by calling
+	 * usbi_get_device_handle_priv() on the libusb_device_handle instance.
+	 */
 	size_t device_handle_priv_size;
 
 	/* Number of bytes to reserve for per-transfer private backend data.
 	 * This private data area is accessible by calling
-	 * usbi_transfer_get_os_priv() on the appropriate usbi_transfer instance.
+	 * usbi_get_transfer_priv() on the usbi_transfer instance.
 	 */
 	size_t transfer_priv_size;
 };