mm: split swap_type_of

swap_type_of is used for two entirely different purposes:

 (1) check what swap type a given device/offset corresponds to
 (2) find the first available swap device that can be written to

Mixing both in a single function creates an unreadable mess.  Create two
separate functions instead, and switch both to pass a dev_t instead of
a struct block_device to further simplify the code.
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

include/linux/swap.h

@@ -467,7 +467,8 @@ extern int swapcache_prepare(swp_entry_t);
 extern void swap_free(swp_entry_t);
 extern void swapcache_free_entries(swp_entry_t *entries, int n);
 extern int free_swap_and_cache(swp_entry_t);
-extern int swap_type_of(dev_t, sector_t, struct block_device **);
+int swap_type_of(dev_t device, sector_t offset);
+int find_first_swap(dev_t *device);
 extern unsigned int count_swap_pages(int, int);
 extern sector_t map_swap_page(struct page *, struct block_device **);
 extern sector_t swapdev_block(int, pgoff_t);

kernel/power/swap.c

@@ -335,12 +335,17 @@ static int swsusp_swap_check(void)
 {
 	int res;
 
-	res = swap_type_of(swsusp_resume_device, swsusp_resume_block,
-			&hib_resume_bdev);
+	if (swsusp_resume_device)
+		res = swap_type_of(swsusp_resume_device, swsusp_resume_block);
+	else
+		res = find_first_swap(&swsusp_resume_device);
 	if (res < 0)
 		return res;
-
 	root_swap = res;
+
+	hib_resume_bdev = bdget(swsusp_resume_device);
+	if (!hib_resume_bdev)
+		return -ENOMEM;
 	res = blkdev_get(hib_resume_bdev, FMODE_WRITE, NULL);
 	if (res)
 		return res;
@@ -349,12 +354,6 @@ static int swsusp_swap_check(void)
 	if (res < 0)
 		blkdev_put(hib_resume_bdev, FMODE_WRITE);
 
-	/*
-	 * Update the resume device to the one actually used,
-	 * so the test_resume mode can use it in case it is
-	 * invoked from hibernate() to test the snapshot.
-	 */
-	swsusp_resume_device = hib_resume_bdev->bd_dev;
 	return res;
 }
 

kernel/power/user.c

@@ -69,8 +69,7 @@ static int snapshot_open(struct inode *inode, struct file *filp)
 	memset(&data->handle, 0, sizeof(struct snapshot_handle));
 	if ((filp->f_flags & O_ACCMODE) == O_RDONLY) {
 		/* Hibernating.  The image device should be accessible. */
-		data->swap = swsusp_resume_device ?
-			swap_type_of(swsusp_resume_device, 0, NULL) : -1;
+		data->swap = swap_type_of(swsusp_resume_device, 0);
 		data->mode = O_RDONLY;
 		data->free_bitmaps = false;
 		error = __pm_notifier_call_chain(PM_HIBERNATION_PREPARE, -1, &nr_calls);
@@ -210,7 +209,6 @@ struct compat_resume_swap_area {
 static int snapshot_set_swap_area(struct snapshot_data *data,
 		void __user *argp)
 {
-	struct block_device *bdev;
 	sector_t offset;
 	dev_t swdev;
 
@@ -237,16 +235,10 @@ static int snapshot_set_swap_area(struct snapshot_data *data,
 	 * User space encodes device types as two-byte values,
 	 * so we need to recode them
 	 */
-	if (!swdev) {
-		data->swap = -1;
-		return -EINVAL;
-	}
-	data->swap = swap_type_of(swdev, offset, &bdev);
+	data->swap = swap_type_of(swdev, offset);
 	if (data->swap < 0)
-		return -ENODEV;
-
-	data->dev = bdev->bd_dev;
-	bdput(bdev);
+		return swdev ? -ENODEV : -EINVAL;
+	data->dev = swdev;
 	return 0;
 }
 

mm/swapfile.c

@@ -1801,13 +1801,12 @@ int free_swap_and_cache(swp_entry_t entry)
  *
  * This is needed for the suspend to disk (aka swsusp).
  */
-int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
+int swap_type_of(dev_t device, sector_t offset)
 {
-	struct block_device *bdev = NULL;
 	int type;
 
-	if (device)
-		bdev = bdget(device);
+	if (!device)
+		return -1;
 
 	spin_lock(&swap_lock);
 	for (type = 0; type < nr_swapfiles; type++) {
@@ -1816,30 +1815,34 @@ int swap_type_of(dev_t device, sector_t offset, struct block_device **bdev_p)
 		if (!(sis->flags & SWP_WRITEOK))
 			continue;
 
-		if (!bdev) {
-			if (bdev_p)
-				*bdev_p = bdgrab(sis->bdev);
-
-			spin_unlock(&swap_lock);
-			return type;
-		}
-		if (bdev == sis->bdev) {
+		if (device == sis->bdev->bd_dev) {
 			struct swap_extent *se = first_se(sis);
 
 			if (se->start_block == offset) {
-				if (bdev_p)
-					*bdev_p = bdgrab(sis->bdev);
-
 				spin_unlock(&swap_lock);
-				bdput(bdev);
 				return type;
 			}
 		}
 	}
 	spin_unlock(&swap_lock);
-	if (bdev)
-		bdput(bdev);
+	return -ENODEV;
+}
+
+int find_first_swap(dev_t *device)
+{
+	int type;
 
+	spin_lock(&swap_lock);
+	for (type = 0; type < nr_swapfiles; type++) {
+		struct swap_info_struct *sis = swap_info[type];
+
+		if (!(sis->flags & SWP_WRITEOK))
+			continue;
+		*device = sis->bdev->bd_dev;
+		spin_unlock(&swap_lock);
+		return type;
+	}
+	spin_unlock(&swap_lock);
 	return -ENODEV;
 }