[slirp] Add libslirp driver for Linux

Add a driver using libslirp to provide a virtual network interface
without requiring root permissions on the host.  This simplifies the
process of running iPXE as a Linux userspace application with network
access.  For example:

  make bin-x86_64-linux/slirp.linux
  ./bin-x86_64-linux/slirp.linux --net slirp

libslirp will provide a built-in emulated DHCP server and NAT router.
Settings such as the boot filename may be controlled via command-line
options.  For example:

  ./bin-x86_64-linux/slirp.linux \
      --net slirp,filename=http://192.168.0.1/boot.ipxe

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

src/include/ipxe/errfile.h

@@ -212,6 +212,7 @@ FILE_LICENCE ( GPL2_OR_LATER_OR_UBDL );
 #define ERRFILE_intelxlvf	     ( ERRFILE_DRIVER | 0x00cd0000 )
 #define ERRFILE_usbblk		     ( ERRFILE_DRIVER | 0x00ce0000 )
 #define ERRFILE_iphone		     ( ERRFILE_DRIVER | 0x00cf0000 )
+#define ERRFILE_slirp		     ( ERRFILE_DRIVER | 0x00d00000 )
 
 #define ERRFILE_aoe			( ERRFILE_NET | 0x00000000 )
 #define ERRFILE_arp			( ERRFILE_NET | 0x00010000 )

src/include/ipxe/linux_api.h

@@ -50,6 +50,9 @@ FILE_LICENCE ( GPL2_OR_LATER );
 #endif
 
 struct sockaddr;
+struct slirp_config;
+struct slirp_callbacks;
+struct Slirp;
 
 extern int linux_errno;
 extern int linux_argc;
@@ -82,5 +85,21 @@ extern ssize_t __asmcall linux_sendto ( int sockfd, const void *buf,
 					const struct sockaddr *dest_addr,
 					size_t addrlen );
 extern const char * __asmcall linux_strerror ( int linux_errno );
+extern struct Slirp * __asmcall
+linux_slirp_new ( const struct slirp_config *config,
+		  const struct slirp_callbacks *callbacks, void *opaque );
+extern void __asmcall linux_slirp_cleanup ( struct Slirp *slirp );
+extern void __asmcall linux_slirp_input ( struct Slirp *slirp,
+					  const uint8_t *pkt, int pkt_len );
+extern void __asmcall
+linux_slirp_pollfds_fill ( struct Slirp *slirp, uint32_t *timeout,
+			   int ( __asmcall * add_poll ) ( int fd, int events,
+							  void *opaque ),
+			   void *opaque );
+extern void __asmcall
+linux_slirp_pollfds_poll ( struct Slirp *slirp, int select_error,
+			   int ( __asmcall * get_revents ) ( int idx,
+							     void *opaque ),
+			   void *opaque );
 
 #endif /* _IPXE_LINUX_API_H */

src/include/ipxe/slirp.h

@@ -0,0 +1,155 @@
+#ifndef _IPXE_SLIRP_H
+#define _IPXE_SLIRP_H
+
+/** @file
+ *
+ * Linux Slirp network driver
+ *
+ */
+
+FILE_LICENCE ( GPL2_OR_LATER );
+
+#include <stdint.h>
+#include <stdbool.h>
+
+/** Ready to be read */
+#define SLIRP_EVENT_IN 0x01
+
+/** Ready to be written */
+#define SLIRP_EVENT_OUT 0x02
+
+/** Exceptional condition */
+#define SLIRP_EVENT_PRI 0x04
+
+/** Error condition */
+#define SLIRP_EVENT_ERR 0x08
+
+/** Hang up */
+#define SLIRP_EVENT_HUP 0x10
+
+/** Slirp device configuration */
+struct slirp_config {
+	/** Configuration version */
+	uint32_t version;
+	/** Restrict to host loopback connections only */
+	int restricted;
+	/** IPv4 is enabled */
+	bool in_enabled;
+	/** IPv4 network */
+	struct in_addr vnetwork;
+	/** IPv4 netmask */
+	struct in_addr vnetmask;
+	/** IPv4 host server address */
+	struct in_addr vhost;
+	/** IPv6 is enabled */
+	bool in6_enabled;
+	/** IPv6 prefix */
+	struct in6_addr vprefix_addr6;
+	/** IPv6 prefix length */
+	uint8_t vprefix_len;
+	/** IPv6 host server address */
+	struct in6_addr vhost6;
+	/** Client hostname */
+	const char *vhostname;
+	/** TFTP server name */
+	const char *tftp_server_name;
+	/** TFTP path prefix */
+	const char *tftp_path;
+	/** Boot filename */
+	const char *bootfile;
+	/** DHCPv4 start address */
+	struct in_addr vdhcp_start;
+	/** DNS IPv4 address */
+	struct in_addr vnameserver;
+	/** DNS IPv6 address */
+	struct in_addr vnameserver6;
+	/** DNS search list */
+	const char **vdnssearch;
+	/** Domain name */
+	const char *vdomainname;
+	/** Interface MTU */
+	size_t if_mtu;
+	/** Interface MRU */
+	size_t if_mru;
+	/** Disable host loopback connections */
+	bool disable_host_loopback;
+	/** Enable emulation (apparently unsafe) */
+	bool enable_emu;
+};
+
+/** Slirp device callbacks */
+struct slirp_callbacks {
+	/**
+	 * Send packet
+	 *
+	 * @v buf		Data buffer
+	 * @v len		Length of data
+	 * @v device		Device opaque pointer
+	 * @ret len		Consumed length (or negative on error)
+	 */
+	ssize_t ( __asmcall * send_packet ) ( const void *buf, size_t len,
+					      void *device );
+	/**
+	 * Print an error message
+	 *
+	 * @v msg		Error message
+	 * @v device		Device opaque pointer
+	 */
+	void ( __asmcall * guest_error ) ( const char *msg, void *device );
+	/**
+	 * Get virtual clock
+	 *
+	 * @v device		Device opaque pointer
+	 * @ret clock_ns	Clock time in nanoseconds
+	 */
+	int64_t ( __asmcall * clock_get_ns ) ( void *device );
+	/**
+	 * Create a new timer
+	 *
+	 * @v callback		Timer callback
+	 * @v opaque		Timer opaque pointer
+	 * @v device		Device opaque pointer
+	 * @ret timer		Timer
+	 */
+	void * ( __asmcall * timer_new ) ( void ( __asmcall * callback )
+					   ( void *opaque ),
+					   void *opaque, void *device );
+	/**
+	 * Delete a timer
+	 *
+	 * @v timer		Timer
+	 * @v device		Device opaque pointer
+	 */
+	void ( __asmcall * timer_free ) ( void *timer, void *device );
+	/**
+	 * Set timer expiry time
+	 *
+	 * @v timer		Timer
+	 * @v expire		Expiry time
+	 * @v device		Device opaque pointer
+	 */
+	void ( __asmcall * timer_mod ) ( void *timer, int64_t expire,
+					 void *device );
+	/**
+	 * Register file descriptor for polling
+	 *
+	 * @v fd		File descriptor
+	 * @v device		Device opaque pointer
+	 */
+	void ( __asmcall * register_poll_fd ) ( int fd, void *device );
+	/**
+	 * Unregister file descriptor
+	 *
+	 * @v fd		File descriptor
+	 * @v device		Device opaque pointer
+	 */
+	void ( __asmcall * unregister_poll_fd ) ( int fd, void *device );
+	/**
+	 * Notify that new events are ready
+	 *
+	 * @v device		Device opaque pointer
+	 */
+	void ( __asmcall * notify ) ( void *device );
+};
+
+#endif /* _IPXE_SLIRP_H */