[xferbuf] Add xfer_buffer() to provide direct access to underlying buffer

Allow data transfer buffer users to provide direct access to their
underlying data transfer buffer.

Signed-off-by: Michael Brown <mcb30@ipxe.org>

diff --git a/src/core/xferbuf.c b/src/core/xferbuf.c
index 7f9780b3af3d06c21726f89347b3212f45d20004..afc72ae765582b83b9fb14d56f89a33897f1e26a 100644 (file)
--- a/src/core/xferbuf.c
+++ b/src/core/xferbuf.c
@@ -283,3 +283,42 @@ struct xfer_buffer_operations xferbuf_umalloc_operations = {
        .write = xferbuf_umalloc_write,
        .read = xferbuf_umalloc_read,
 };
+
+/**
+ * Get underlying data transfer buffer
+ *
+ * @v interface                Data transfer interface
+ * @ret xferbuf                Data transfer buffer, or NULL on error
+ *
+ * This call will check that the xfer_buffer() handler belongs to the
+ * destination interface which also provides xfer_deliver() for this
+ * interface.
+ *
+ * This is done to prevent accidental accesses to a data transfer
+ * buffer which may be located behind a non-transparent datapath via a
+ * series of pass-through interfaces.
+ */
+struct xfer_buffer * xfer_buffer ( struct interface *intf ) {
+       struct interface *dest;
+       xfer_buffer_TYPE ( void * ) *op =
+               intf_get_dest_op ( intf, xfer_buffer, &dest );
+       void *object = intf_object ( dest );
+       struct interface *xfer_deliver_dest;
+       struct xfer_buffer *xferbuf;
+
+       /* Check that this operation is provided by the same interface
+        * which handles xfer_deliver().
+        */
+       intf_get_dest_op ( intf, xfer_deliver, &xfer_deliver_dest );
+
+       if ( op && ( dest == xfer_deliver_dest ) ) {
+               xferbuf = op ( object );
+       } else {
+               /* Default is to not have a data transfer buffer */
+               xferbuf = NULL;
+       }
+
+       intf_put ( xfer_deliver_dest );
+       intf_put ( dest );
+       return xferbuf;
+}

diff --git a/src/include/ipxe/xferbuf.h b/src/include/ipxe/xferbuf.h
index f2f3362529bfe6e9015b3cc9bc7d88ea7933e6d4..cb0b1a0e891ec6e9f836b13ed836a27a105e7a31 100644 (file)
--- a/src/include/ipxe/xferbuf.h
+++ b/src/include/ipxe/xferbuf.h
@@ -12,6 +12,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #include <stdint.h>
 #include <ipxe/iobuf.h>
 #include <ipxe/uaccess.h>
+#include <ipxe/interface.h>
 #include <ipxe/xfer.h>
 
 /** A data transfer buffer */
@@ -97,4 +98,8 @@ extern int xferbuf_deliver ( struct xfer_buffer *xferbuf,
                             struct io_buffer *iobuf,
                             struct xfer_metadata *meta );
 
+extern struct xfer_buffer * xfer_buffer ( struct interface *intf );
+#define xfer_buffer_TYPE( object_type ) \
+       typeof ( struct xfer_buffer * ( object_type ) )
+
 #endif /* _IPXE_XFERBUF_H */