block: Add BLKROTATIONAL ioctl

Introduce an ioctl which permits applications to query whether a block
device is rotational.
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

block/compat_ioctl.c

@@ -719,6 +719,9 @@ long compat_blkdev_ioctl(struct file *file, unsigned cmd, unsigned long arg)
 	case BLKSECTGET:
 		return compat_put_ushort(arg,
 					 queue_max_sectors(bdev_get_queue(bdev)));
+	case BLKROTATIONAL:
+		return compat_put_ushort(arg,
+					 !blk_queue_nonrot(bdev_get_queue(bdev)));
 	case BLKRASET: /* compatible, but no compat_ptr (!) */
 	case BLKFRASET:
 		if (!capable(CAP_SYS_ADMIN))

block/ioctl.c

@@ -278,6 +278,8 @@ int blkdev_ioctl(struct block_device *bdev, fmode_t mode, unsigned cmd,
 		return put_uint(arg, bdev_discard_zeroes_data(bdev));
 	case BLKSECTGET:
 		return put_ushort(arg, queue_max_sectors(bdev_get_queue(bdev)));
+	case BLKROTATIONAL:
+		return put_ushort(arg, !blk_queue_nonrot(bdev_get_queue(bdev)));
 	case BLKRASET:
 	case BLKFRASET:
 		if(!capable(CAP_SYS_ADMIN))

include/linux/fs.h

@@ -319,6 +319,7 @@ struct inodes_stat_t {
 #define BLKPBSZGET _IO(0x12,123)
 #define BLKDISCARDZEROES _IO(0x12,124)
 #define BLKSECDISCARD _IO(0x12,125)
+#define BLKROTATIONAL _IO(0x12,126)
 
 #define BMAP_IOCTL 1		/* obsolete - kept for compatibility */
 #define FIBMAP	   _IO(0x00,1)	/* bmap access */