floppy: switch to one queue per drive instead of sharing a queue

Pretty straight forward conversion. Note that we do round-robin
between the drives that have available requests, before we simply
used the drive that the IO scheduler told us to. Since the IO
scheduler doesn't care about multiple devices per queue, the resulting
sort would not have made sense.

Fixed by Vivek to get rid of a double lock problem in set_next_request()
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>
Signed-off-by: Vivek Goyal <vgoyal@redhat.com>

drivers/block/floppy.c

@@ -258,8 +258,8 @@ static int irqdma_allocated;
 #include <linux/completion.h>
 
 static struct request *current_req;
-static struct request_queue *floppy_queue;
 static void do_fd_request(struct request_queue *q);
+static int set_next_request(void);
 
 #ifndef fd_get_dma_residue
 #define fd_get_dma_residue() get_dma_residue(FLOPPY_DMA)
@@ -413,6 +413,7 @@ static struct gendisk *disks[N_DRIVE];
 static struct block_device *opened_bdev[N_DRIVE];
 static DEFINE_MUTEX(open_lock);
 static struct floppy_raw_cmd *raw_cmd, default_raw_cmd;
+static int fdc_queue;
 
 /*
  * This struct defines the different floppy types.
@@ -890,8 +891,8 @@ static void unlock_fdc(void)
 	del_timer(&fd_timeout);
 	cont = NULL;
 	clear_bit(0, &fdc_busy);
-	if (current_req || blk_peek_request(floppy_queue))
-		do_fd_request(floppy_queue);
+	if (current_req || set_next_request())
+		do_fd_request(current_req->q);
 	spin_unlock_irqrestore(&floppy_lock, flags);
 	wake_up(&fdc_wait);
 }
@@ -2243,8 +2244,8 @@ static void floppy_end_request(struct request *req, int error)
  * logical buffer */
 static void request_done(int uptodate)
 {
-	struct request_queue *q = floppy_queue;
 	struct request *req = current_req;
+	struct request_queue *q;
 	unsigned long flags;
 	int block;
 	char msg[sizeof("request done ") + sizeof(int) * 3];
@@ -2258,6 +2259,8 @@ static void request_done(int uptodate)
 		return;
 	}
 
+	q = req->q;
+
 	if (uptodate) {
 		/* maintain values for invalidation on geometry
 		 * change */
@@ -2811,6 +2814,28 @@ static int make_raw_rw_request(void)
 	return 2;
 }
 
+/*
+ * Round-robin between our available drives, doing one request from each
+ */
+static int set_next_request(void)
+{
+	struct request_queue *q;
+	int old_pos = fdc_queue;
+
+	do {
+		q = disks[fdc_queue]->queue;
+		if (++fdc_queue == N_DRIVE)
+			fdc_queue = 0;
+		if (q) {
+			current_req = blk_fetch_request(q);
+			if (current_req)
+				break;
+		}
+	} while (fdc_queue != old_pos);
+
+	return current_req != NULL;
+}
+
 static void redo_fd_request(void)
 {
 	int drive;
@@ -2822,17 +2847,17 @@ static void redo_fd_request(void)
 
 do_request:
 	if (!current_req) {
-		struct request *req;
+		int pending;
 
-		spin_lock_irq(floppy_queue->queue_lock);
-		req = blk_fetch_request(floppy_queue);
-		spin_unlock_irq(floppy_queue->queue_lock);
-		if (!req) {
+		spin_lock_irq(&floppy_lock);
+		pending = set_next_request();
+		spin_unlock_irq(&floppy_lock);
+
+		if (!pending) {
 			do_floppy = NULL;
 			unlock_fdc();
 			return;
 		}
-		current_req = req;
 	}
 	drive = (long)current_req->rq_disk->private_data;
 	set_fdc(drive);
@@ -4165,6 +4190,13 @@ static int __init floppy_init(void)
 			goto out_put_disk;
 		}
 
+		disks[dr]->queue = blk_init_queue(do_fd_request, &floppy_lock);
+		if (!disks[dr]->queue) {
+			err = -ENOMEM;
+			goto out_put_disk;
+		}
+
+		blk_queue_max_hw_sectors(disks[dr]->queue, 64);
 		disks[dr]->major = FLOPPY_MAJOR;
 		disks[dr]->first_minor = TOMINOR(dr);
 		disks[dr]->fops = &floppy_fops;
@@ -4183,13 +4215,6 @@ static int __init floppy_init(void)
 	if (err)
 		goto out_unreg_blkdev;
 
-	floppy_queue = blk_init_queue(do_fd_request, &floppy_lock);
-	if (!floppy_queue) {
-		err = -ENOMEM;
-		goto out_unreg_driver;
-	}
-	blk_queue_max_hw_sectors(floppy_queue, 64);
-
 	blk_register_region(MKDEV(FLOPPY_MAJOR, 0), 256, THIS_MODULE,
 			    floppy_find, NULL, NULL);
 
@@ -4317,7 +4342,6 @@ static int __init floppy_init(void)
 
 		/* to be cleaned up... */
 		disks[drive]->private_data = (void *)(long)drive;
-		disks[drive]->queue = floppy_queue;
 		disks[drive]->flags |= GENHD_FL_REMOVABLE;
 		disks[drive]->driverfs_dev = &floppy_device[drive].dev;
 		add_disk(disks[drive]);
@@ -4333,8 +4357,6 @@ static int __init floppy_init(void)
 		floppy_release_irq_and_dma();
 out_unreg_region:
 	blk_unregister_region(MKDEV(FLOPPY_MAJOR, 0), 256);
-	blk_cleanup_queue(floppy_queue);
-out_unreg_driver:
 	platform_driver_unregister(&floppy_driver);
 out_unreg_blkdev:
 	unregister_blkdev(FLOPPY_MAJOR, "fd");
@@ -4342,6 +4364,8 @@ static int __init floppy_init(void)
 	while (dr--) {
 		del_timer(&motor_off_timer[dr]);
 		put_disk(disks[dr]);
+		if (disks[dr]->queue)
+			blk_cleanup_queue(disks[dr]->queue);
 	}
 	return err;
 }
@@ -4550,11 +4574,11 @@ static void __exit floppy_module_exit(void)
 			platform_device_unregister(&floppy_device[drive]);
 		}
 		put_disk(disks[drive]);
+		blk_cleanup_queue(disks[drive]->queue);
 	}
 
 	del_timer_sync(&fd_timeout);
 	del_timer_sync(&fd_timer);
-	blk_cleanup_queue(floppy_queue);
 
 	if (atomic_read(&usage_count))
 		floppy_release_irq_and_dma();