[PATCH] USB: URB_ASYNC_UNLINK flag removed from the kernel

29 July 2005, Cambridge, MA:

This afternoon Alan Stern submitted a patch to remove the URB_ASYNC_UNLINK
flag from the Linux kernel.  Mr. Stern explained, "This flag is a relic
from an earlier, less-well-designed system.  For over a year it hasn't
been used for anything other than printing warning messages."

An anonymous spokesman for the Linux kernel development community
commented, "This is exactly the sort of thing we see happening all the
time.  As the kernel evolves, support for old techniques and old code can
be jettisoned and replaced by newer, better approaches.  Proprietary
operating systems do not have the freedom or flexibility to change so
quickly."

Mr. Stern, a staff member at Harvard University's Rowland Institute who
works on Linux only as a hobby, noted that the patch (labelled as548) did
not update two files, keyspan.c and option.c, in the USB drivers' "serial"
subdirectory.  "Those files need more extensive changes," he remarked.
"They examine the status field of several URBs at times when they're not
supposed to.  That will need to be fixed before the URB_ASYNC_UNLINK flag
is removed."

Greg Kroah-Hartman, the kernel maintainer responsible for overseeing all
of Linux's USB drivers, did not respond to our inquiries or return our
calls.  His only comment was "Applied, thanks."

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

2 files changed, 5 insertions, 25 deletions

diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index 88d1b37..7419724 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -48,7 +48,6 @@ static int usb_start_wait_urb(struct urb *urb, int timeout, int* actual_length)
 
 	init_completion(&done); 	
 	urb->context = &done;
-	urb->transfer_flags |= URB_ASYNC_UNLINK;
 	urb->actual_length = 0;
 	status = usb_submit_urb(urb, GFP_NOIO);
 
@@ -357,8 +356,7 @@ int usb_sg_init (
 	if (!io->urbs)
 		goto nomem;
 
-	urb_flags = URB_ASYNC_UNLINK | URB_NO_TRANSFER_DMA_MAP
-			| URB_NO_INTERRUPT;
+	urb_flags = URB_NO_TRANSFER_DMA_MAP | URB_NO_INTERRUPT;
 	if (usb_pipein (pipe))
 		urb_flags |= URB_SHORT_NOT_OK;
 
diff --git a/drivers/usb/core/urb.c b/drivers/usb/core/urb.c
index c0feee2..c846fef 100644
--- a/drivers/usb/core/urb.c
+++ b/drivers/usb/core/urb.c
@@ -309,9 +309,8 @@ int usb_submit_urb(struct urb *urb, unsigned mem_flags)
 	unsigned int	allowed;
 
 	/* enforce simple/standard policy */
-	allowed = URB_ASYNC_UNLINK;	// affects later unlinks
-	allowed |= (URB_NO_TRANSFER_DMA_MAP | URB_NO_SETUP_DMA_MAP);
-	allowed |= URB_NO_INTERRUPT;
+	allowed = (URB_NO_TRANSFER_DMA_MAP | URB_NO_SETUP_DMA_MAP |
+			URB_NO_INTERRUPT);
 	switch (temp) {
 	case PIPE_BULK:
 		if (is_out)
@@ -400,14 +399,8 @@ int usb_submit_urb(struct urb *urb, unsigned mem_flags)
  * canceled (rather than any other code) and will quickly be removed
  * from host controller data structures.
  *
- * In the past, clearing the URB_ASYNC_UNLINK transfer flag for the
- * URB indicated that the request was synchronous.  This usage is now
- * deprecated; if the flag is clear the call will be forwarded to
- * usb_kill_urb() and the return value will be 0.  In the future, drivers
- * should call usb_kill_urb() directly for synchronous unlinking.
- *
- * When the URB_ASYNC_UNLINK transfer flag for the URB is set, this
- * request is asynchronous.  Success is indicated by returning -EINPROGRESS,
+ * This request is always asynchronous.
+ * Success is indicated by returning -EINPROGRESS,
  * at which time the URB will normally have been unlinked but not yet
  * given back to the device driver.  When it is called, the completion
  * function will see urb->status == -ECONNRESET.  Failure is indicated
@@ -453,17 +446,6 @@ int usb_unlink_urb(struct urb *urb)
 {
 	if (!urb)
 		return -EINVAL;
-	if (!(urb->transfer_flags & URB_ASYNC_UNLINK)) {
-#ifdef CONFIG_DEBUG_KERNEL
-		if (printk_ratelimit()) {
-			printk(KERN_NOTICE "usb_unlink_urb() is deprecated for "
-				"synchronous unlinks.  Use usb_kill_urb() instead.\n");
-			WARN_ON(1);
-		}
-#endif
-		usb_kill_urb(urb);
-		return 0;
-	}
 	if (!(urb->dev && urb->dev->bus && urb->dev->bus->op))
 		return -ENODEV;
 	return urb->dev->bus->op->unlink_urb(urb, -ECONNRESET);