virtio-blk: Clean up signedness casts

Switch to size_t type for ->bio_bcount in struct bio and clean up
virtio-blk signedness casts.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>

drivers/virtio-blk.cc

@@ -257,12 +257,12 @@ int virtio_blk::make_virtio_request(struct bio* bio)
 
         // need to break a contiguous buffers that > 4k into several physical page mapping
         // even if the virtual space is contiguous.
-        long len = 0;
-        int offset = reinterpret_cast<long>(bio->bio_data) & 0xfff;
+        size_t len = 0;
+        auto offset = reinterpret_cast<size_t>(bio->bio_data) & 0xfff;
         void *base = bio->bio_data;
         while (len != bio->bio_bcount) {
-            long size = std::min(bio->bio_bcount - len, (long)mmu::page_size);
-            if (offset + size > (long)mmu::page_size)
+            auto size = std::min(bio->bio_bcount - len, mmu::page_size);
+            if (offset + size > mmu::page_size)
                 size = mmu::page_size - offset;
             len += size;
             queue->_sg_vec.push_back(vring::sg_node(mmu::virt_to_phys(base), size, (type == VIRTIO_BLK_T_OUT)? vring_desc::VRING_DESC_F_READ:vring_desc::VRING_DESC_F_WRITE));

include/osv/bio.h

@@ -81,7 +81,7 @@ struct bio {
 	uint8_t	bio_flags;		/* General flags. */
 	struct device *bio_dev;		/* Device to do I/O on. */
 	off_t	bio_offset;		/* Offset into file. */
-	long	bio_bcount;		/* Valid bytes in buffer. */
+	size_t	bio_bcount;		/* Valid bytes in buffer. */
 	void	*bio_data;		/* Memory, superblocks, indirect etc. */
 	int	bio_error;		/* Errno for BIO_ERROR. */
 	long	bio_resid;		/* Remaining I/O in bytes. */