kvm tools: Implement VIRTIO_BLK_T_GET_ID

Return device id when requested by virtio-blk.
Device id is currently based on the device information and the inode
number of the underlying disk image.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
Signed-off-by: Pekka Enberg <penberg@kernel.org>

disk/core.c

@@ -207,3 +207,14 @@ ssize_t disk_image__write(struct disk_image *disk, u64 sector, const struct iove
 
 	return total;
 }
+
+ssize_t disk_image__get_serial(struct disk_image *disk, void *buffer, ssize_t *len)
+{
+	struct stat st;
+
+	if (fstat(disk->fd, &st) != 0)
+		return 0;
+
+	*len = snprintf(buffer, *len, "%lu%lu%lu", st.st_dev, st.st_rdev, st.st_ino);
+	return *len;
+}

include/kvm/disk-image.h

@@ -59,6 +59,7 @@ void disk_image__close_all(struct disk_image **disks, int count);
 int disk_image__flush(struct disk_image *disk);
 ssize_t disk_image__read(struct disk_image *disk, u64 sector, const struct iovec *iov, int iovcount);
 ssize_t disk_image__write(struct disk_image *disk, u64 sector, const struct iovec *iov, int iovcount);
+ssize_t disk_image__get_serial(struct disk_image *disk, void *buffer, ssize_t *len);
 
 struct disk_image *raw_image__probe(int fd, struct stat *st, bool readonly);
 struct disk_image *blkdev__probe(const char *filename, struct stat *st);

virtio/blk.c

@@ -152,6 +152,10 @@ static void virtio_blk_do_io_request(struct kvm *kvm, void *param)
 	case VIRTIO_BLK_T_FLUSH:
 		block_cnt       = disk_image__flush(bdev->disk);
 		break;
+	case VIRTIO_BLK_T_GET_ID:
+		block_cnt	= VIRTIO_BLK_ID_BYTES;
+		disk_image__get_serial(bdev->disk, (iov + 1)->iov_base, &block_cnt);
+		break;
 	default:
 		pr_warning("request type %d", req->type);
 		block_cnt	= -1;