[PATCH 6/8] zram: allow automatic new zram device_id assignment

[Sergey Senozhatsky <sergey.senozhatsky@gmail.com>]

If no particular device_id was requested (passed -1 to zram_add()) during new zram
device creation, generate one automatically and return it back. So, schematically,
device creation can be done as:

	dev_id = ioctl ZRAM_CTL_ADD -1
	# dev_id == 1 or error code
	init device zram1

	dev_id = ioctl ZRAM_CTL_ADD -1
	# dev_id == 2 or error code
	init device zram2
	...

Signed-off-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
---
 drivers/block/zram/zram_drv.c | 9 ++++++++-
 1 file changed, 8 insertions(+), 1 deletion(-)

diff --git a/drivers/block/zram/zram_drv.c b/drivers/block/zram/zram_drv.c
index 0154c2d4..5804dda 100644
--- a/drivers/block/zram/zram_drv.c
+++ b/drivers/block/zram/zram_drv.c
@@ -1090,8 +1090,15 @@ static int zram_add(int device_id)
 	if (!zram)
 		return ret;
 
-	ret = idr_alloc(&zram_index_idr, zram, device_id,
+	if (device_id < 0) {
+		/* generate new device_id */
+		ret = idr_alloc(&zram_index_idr, zram, 0, 0, GFP_KERNEL);
+		device_id = ret;
+	} else {
+		/* use specific device_id */
+		ret = idr_alloc(&zram_index_idr, zram, device_id,
 			device_id + 1, GFP_KERNEL);
+	}
 	if (ret < 0)
 		goto out_free_dev;
 
-- 
2.3.1.167.g7f4ba4b