qrap: Find qemu command if not passed, patch command line

It might be impractical to pass options to qrap when using libvirt,
because the <emulator/> tag expects a path to an executable, without
further arguments.

If the first argument is not a plausible socket number, and the
second argument is not a valid executable, look up a qemu command
from a list of possible names, then start it patching the command line
to include the -netdev fd= parameter corresponding to the AF_UNIX
domain socket we just opened.

Signed-off-by: Stefano Brivio <sbrivio@redhat.com>

2 files changed, 82 insertions, 10 deletions

diff --git a/Makefile b/Makefile
index 326e717..213020b 100644
--- a/Makefile
+++ b/Makefile
@@ -6,7 +6,7 @@ passt: passt.c passt.h arp.c arp.h dhcp.c dhcp.h dhcpv6.c dhcpv6.h ndp.c ndp.h s
 	$(CC) $(CFLAGS) passt.c arp.c dhcp.c dhcpv6.c ndp.c siphash.c tap.c icmp.c tcp.c udp.c util.c -o passt
 
 qrap: qrap.c passt.h
-	$(CC) $(CFLAGS) qrap.c -o qrap
+	$(CC) $(CFLAGS) -DARCH=\"$(shell uname -m)\" qrap.c -o qrap
 
 .PHONY: clean
 clean:
diff --git a/qrap.c b/qrap.c
index 3dc525a..7f27d47 100644
--- a/qrap.c
+++ b/qrap.c
@@ -19,20 +19,36 @@
 #include <sys/socket.h>
 #include <sys/un.h>
 #include <errno.h>
-#include <limits.h>
 #include <linux/if_ether.h>
 #include <linux/ipv6.h>
+#include <linux/limits.h>
+#include <limits.h>
 #include <net/if.h>
 
 #include "passt.h"
 
+static char *qemu_names[] = {
+	"kvm",
+	"qemu-kvm",
+#ifdef ARCH
+	"qemu-system-" ARCH,
+#endif
+	NULL,
+};
+
+#define DEFAULT_FD	5
+
 /**
  * usage() - Print usage and exit
  * @name:	Executable name
  */
 void usage(const char *name)
 {
-	fprintf(stderr, "Usage: %s FDNUM QEMU_CMD ...\n", name);
+	fprintf(stderr, "Usage: %s [FDNUM QEMU_CMD] ...\n", name);
+	fprintf(stderr, "\n");
+	fprintf(stderr, "If first and second arguments aren't a socket number\n"
+			"and a path, %s will try to locate a qemu binary\n"
+			"and directly patch the command line\n", name);
 
 	exit(EXIT_FAILURE);
 }
@@ -46,20 +62,60 @@ void usage(const char *name)
  */
 int main(int argc, char **argv)
 {
+	char *qemu_argv[ARG_MAX], net_id[ARG_MAX] = { 0 }, *net_id_end;
 	struct sockaddr_un addr = {
 		.sun_family = AF_UNIX,
 		.sun_path = UNIX_SOCK_PATH,
 	};
+	int i, s, qemu_argc = 0;
+	char fd_str[ARG_MAX];
 	long fd;
-	int s;
 
-	if (argc < 3)
-		usage(argv[0]);
+	if (argc >= 3) {
+		fd = strtol(argv[1], NULL, 0);
+		if (fd >= 3 && fd < INT_MAX && !errno) {
+			char env_path[ARG_MAX], *p, command[ARG_MAX];
+
+			strncpy(env_path, getenv("PATH"), ARG_MAX);
+			p = strtok(env_path, ":");
+			while (p) {
+				snprintf(command, ARG_MAX, "%s/%s", p, argv[2]);
+				if (!access(command, X_OK))
+					goto valid_args;
+
+				p = strtok(NULL, ":");
+			}
+		}
+	}
+
+	fd = DEFAULT_FD;
+	for (qemu_argc = 1, i = 1; i < argc; i++) {
+		char *p;
+
+		if (!strcmp(argv[i], "-net") || (!strcmp(argv[i], "-netdev"))) {
+			i++;
+			continue;
+		}
 
-	fd = strtol(argv[1], NULL, 0);
-	if (fd < 3 || fd > INT_MAX || errno)
-		usage(argv[0]);
+		if (!*net_id && (p = strstr(argv[i], ",netdev=")))
+			strncpy(net_id, p + strlen(",netdev="), ARG_MAX);
 
+		qemu_argv[qemu_argc++] = argv[i];
+	}
+
+	if (*net_id) {
+		net_id_end = strpbrk(net_id, ", ");
+		if (net_id_end)
+			*net_id_end = 0;
+	}
+
+	qemu_argv[qemu_argc++] = "-netdev";
+	snprintf(fd_str, ARG_MAX, "socket,fd=%u,id=%s", DEFAULT_FD,
+		 *net_id ? net_id : "hostnet0");
+	qemu_argv[qemu_argc++] = fd_str;
+	qemu_argv[qemu_argc] = NULL;
+
+valid_args:
 	s = socket(AF_UNIX, SOCK_STREAM, 0);
 	if (s < 0) {
 		perror("socket");
@@ -78,7 +134,23 @@ int main(int argc, char **argv)
 
 	close(s);
 
-	execvp(argv[2], argv + 2);
+	if (qemu_argc) {
+		char *name;
+
+		for (name = qemu_names[0]; name; name++) {
+			qemu_argv[0] = name;
+			execvp(name, qemu_argv);
+			if (errno != ENOENT) {
+				perror("execvp");
+				usage(argv[0]);
+			}
+		}
+		if (errno == ENOENT)
+			fprintf(stderr, "Couldn't find qemu command\n");
+	} else {
+		execvp(argv[2], argv + 2);
+	}
+
 	perror("execvp");
 
 	return EXIT_FAILURE;