[PATCH 2/4] pif: Introduce notion of passt/pasta interface

[David Gibson <david@gibson.dropbear.id.au>]

We have several possible ways of communicating with other entities.  We use
sockets to communicate with the host and other network sites, but also in
a different context to communicate "spliced" channels to a namespace.  We
also use a tuntap device or a qemu socket to communicate with the namespace
or guest.

For the time being these are just defined implicitly by how we structure
things.  However, there are other communication channels we want to use in
future (e.g. virtio-user), and we want to allow more flexible forwarding
between those.  To accomplish that we're going to want a specific way of
referring to those channels.

Introduce the concept of a "passt/pasta interface" or "pif" representing a
specific channel to communicate network data.  Each pif is assumed to be
associated with a specific network namespace in the broad sense (that is
as a place where IP addresses have a consistent meaning - not the Linux
specific sense).  But there could be multiple pifs communicating with the
same namespace (e.g. the spliced and tap interfaces in pasta).

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
---
 Makefile |  2 +-
 pif.h    | 36 ++++++++++++++++++++++++++++++++++++
 2 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 pif.h

diff --git a/Makefile b/Makefile
index 0324fdd..55972b1 100644
--- a/Makefile
+++ b/Makefile
@@ -53,7 +53,7 @@ MANPAGES = passt.1 pasta.1 qrap.1
 
 PASST_HEADERS = arch.h arp.h checksum.h conf.h dhcp.h dhcpv6.h icmp.h \
 	inany.h isolation.h lineread.h log.h ndp.h netlink.h packet.h passt.h \
-	pasta.h pcap.h port_fwd.h siphash.h tap.h tcp.h tcp_conn.h \
+	pasta.h pcap.h pif.h port_fwd.h siphash.h tap.h tcp.h tcp_conn.h \
 	tcp_splice.h udp.h util.h
 HEADERS = $(PASST_HEADERS) seccomp.h
 
diff --git a/pif.h b/pif.h
new file mode 100644
index 0000000..edd4fee
--- /dev/null
+++ b/pif.h
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ *
+ * Passt/pasta interface types and IDs
+ */
+#ifndef PIF_H
+#define PIF_H
+
+/**
+ * enum pif_type - Type of passt/pasta interface ("pif")
+ *
+ * Pifs can be an L4 level channel (sockets) or an L2 level channel (tap device
+ * or qemu socket).
+ */
+enum pif_type {
+	/* Invalid or not present pif */
+	PIF_NONE = 0,
+	/* Host socket interface */
+	PIF_HOST,
+	/* Qemu socket or namespace tuntap interface */
+	PIF_TAP,
+	/* Namespace socket interface for splicing */
+	PIF_SPLICE,
+};
+	
+/**
+ * pif_id - Index for passt/pasta interface ("pif")
+ *
+ * This represents a specific instance of an interface.  For now, we don't have
+ * multiple instances of the same type, so we use the same values as for
+ * pif_type here.  That might change in future.
+ */
+typedef uint8_t pif_id;
+
+#endif /* PIF_H */
-- 
@@ -0,0 +1,36 @@
+/* SPDX-License-Identifier: GPL-2.0-or-later
+ * Copyright Red Hat
+ * Author: David Gibson <david@gibson.dropbear.id.au>
+ *
+ * Passt/pasta interface types and IDs
+ */
+#ifndef PIF_H
+#define PIF_H
+
+/**
+ * enum pif_type - Type of passt/pasta interface ("pif")
+ *
+ * Pifs can be an L4 level channel (sockets) or an L2 level channel (tap device
+ * or qemu socket).
+ */
+enum pif_type {
+	/* Invalid or not present pif */
+	PIF_NONE = 0,
+	/* Host socket interface */
+	PIF_HOST,
+	/* Qemu socket or namespace tuntap interface */
+	PIF_TAP,
+	/* Namespace socket interface for splicing */
+	PIF_SPLICE,
+};
+	
+/**
+ * pif_id - Index for passt/pasta interface ("pif")
+ *
+ * This represents a specific instance of an interface.  For now, we don't have
+ * multiple instances of the same type, so we use the same values as for
+ * pif_type here.  That might change in future.
+ */
+typedef uint8_t pif_id;
+
+#endif /* PIF_H */
-- 
2.41.0