USB: g_file_storage: don't send padding when stall=n

This patch (as1455) removes the extra padding sent by g_file_storage
and g_mass_storage when the gadget wants to send less data than
requested by the host and isn't allowed to halt the bulk-IN endpoint.

Although the Bulk-Only Transport specification requires the padding to
be present, it isn't truly needed since the transfer will be terminated
by a short packet anyway.  Furthermore, many existing devices don't
bother to send any padding.

Signed-off-by: Alan Stern <stern@rowland.harvard.edu>
Acked-By: Michal Nazarewicz <mina86@mina86.com>
CC: Roger Quadros <roger.quadros@nokia.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

drivers/usb/gadget/f_mass_storage.c

@@ -1569,37 +1569,6 @@ static int wedge_bulk_in_endpoint(struct fsg_dev *fsg)
 	return rc;
 }
 
-static int pad_with_zeros(struct fsg_dev *fsg)
-{
-	struct fsg_buffhd	*bh = fsg->common->next_buffhd_to_fill;
-	u32			nkeep = bh->inreq->length;
-	u32			nsend;
-	int			rc;
-
-	bh->state = BUF_STATE_EMPTY;		/* For the first iteration */
-	fsg->common->usb_amount_left = nkeep + fsg->common->residue;
-	while (fsg->common->usb_amount_left > 0) {
-
-		/* Wait for the next buffer to be free */
-		while (bh->state != BUF_STATE_EMPTY) {
-			rc = sleep_thread(fsg->common);
-			if (rc)
-				return rc;
-		}
-
-		nsend = min(fsg->common->usb_amount_left, FSG_BUFLEN);
-		memset(bh->buf + nkeep, 0, nsend - nkeep);
-		bh->inreq->length = nsend;
-		bh->inreq->zero = 0;
-		start_transfer(fsg, fsg->bulk_in, bh->inreq,
-			       &bh->inreq_busy, &bh->state);
-		bh = fsg->common->next_buffhd_to_fill = bh->next;
-		fsg->common->usb_amount_left -= nsend;
-		nkeep = 0;
-	}
-	return 0;
-}
-
 static int throw_away_data(struct fsg_common *common)
 {
 	struct fsg_buffhd	*bh;
@@ -1686,6 +1655,10 @@ static int finish_reply(struct fsg_common *common)
 		if (common->data_size == 0) {
 			/* Nothing to send */
 
+		/* Don't know what to do if common->fsg is NULL */
+		} else if (!fsg_is_set(common)) {
+			rc = -EIO;
+
 		/* If there's no residue, simply send the last buffer */
 		} else if (common->residue == 0) {
 			bh->inreq->zero = 0;
@@ -1694,24 +1667,19 @@ static int finish_reply(struct fsg_common *common)
 			common->next_buffhd_to_fill = bh->next;
 
 		/*
-		 * For Bulk-only, if we're allowed to stall then send the
-		 * short packet and halt the bulk-in endpoint.  If we can't
-		 * stall, pad out the remaining data with 0's.
+		 * For Bulk-only, mark the end of the data with a short
+		 * packet.  If we are allowed to stall, halt the bulk-in
+		 * endpoint.  (Note: This violates the Bulk-Only Transport
+		 * specification, which requires us to pad the data if we
+		 * don't halt the endpoint.  Presumably nobody will mind.)
 		 */
-		} else if (common->can_stall) {
+		} else {
 			bh->inreq->zero = 1;
 			if (!start_in_transfer(common, bh))
-				/* Don't know what to do if
-				 * common->fsg is NULL */
 				rc = -EIO;
 			common->next_buffhd_to_fill = bh->next;
-			if (common->fsg)
+			if (common->can_stall)
 				rc = halt_bulk_in_endpoint(common->fsg);
-		} else if (fsg_is_set(common)) {
-			rc = pad_with_zeros(common->fsg);
-		} else {
-			/* Don't know what to do if common->fsg is NULL */
-			rc = -EIO;
 		}
 		break;
 

drivers/usb/gadget/file_storage.c

@@ -1932,37 +1932,6 @@ static int wedge_bulk_in_endpoint(struct fsg_dev *fsg)
 	return rc;
 }
 
-static int pad_with_zeros(struct fsg_dev *fsg)
-{
-	struct fsg_buffhd	*bh = fsg->next_buffhd_to_fill;
-	u32			nkeep = bh->inreq->length;
-	u32			nsend;
-	int			rc;
-
-	bh->state = BUF_STATE_EMPTY;		// For the first iteration
-	fsg->usb_amount_left = nkeep + fsg->residue;
-	while (fsg->usb_amount_left > 0) {
-
-		/* Wait for the next buffer to be free */
-		while (bh->state != BUF_STATE_EMPTY) {
-			rc = sleep_thread(fsg);
-			if (rc)
-				return rc;
-		}
-
-		nsend = min(fsg->usb_amount_left, (u32) mod_data.buflen);
-		memset(bh->buf + nkeep, 0, nsend - nkeep);
-		bh->inreq->length = nsend;
-		bh->inreq->zero = 0;
-		start_transfer(fsg, fsg->bulk_in, bh->inreq,
-				&bh->inreq_busy, &bh->state);
-		bh = fsg->next_buffhd_to_fill = bh->next;
-		fsg->usb_amount_left -= nsend;
-		nkeep = 0;
-	}
-	return 0;
-}
-
 static int throw_away_data(struct fsg_dev *fsg)
 {
 	struct fsg_buffhd	*bh;
@@ -2066,18 +2035,20 @@ static int finish_reply(struct fsg_dev *fsg)
 			}
 		}
 
-		/* For Bulk-only, if we're allowed to stall then send the
-		 * short packet and halt the bulk-in endpoint.  If we can't
-		 * stall, pad out the remaining data with 0's. */
+		/*
+		 * For Bulk-only, mark the end of the data with a short
+		 * packet.  If we are allowed to stall, halt the bulk-in
+		 * endpoint.  (Note: This violates the Bulk-Only Transport
+		 * specification, which requires us to pad the data if we
+		 * don't halt the endpoint.  Presumably nobody will mind.)
+		 */
 		else {
-			if (mod_data.can_stall) {
 			bh->inreq->zero = 1;
 			start_transfer(fsg, fsg->bulk_in, bh->inreq,
 					&bh->inreq_busy, &bh->state);
 			fsg->next_buffhd_to_fill = bh->next;
+			if (mod_data.can_stall)
 				rc = halt_bulk_in_endpoint(fsg);
-			} else
-				rc = pad_with_zeros(fsg);
 		}
 		break;