[PATCH v2 2/2] kvm tools: Add '--rootfs' and '--binsh'

[Sasha Levin <levinsasha928@gmail.com>]

This patch adds 2 new flags:

 --rootfs [path] - Specifies a path to use as rootfs. The path will be mounted
using virtio-9p and booted from.
Easiest way to test it is to mount the sample image we recommend with kvm tool
(http://wiki.qemu.org/download/linux-0.2.img.bz2) and mounting it somewhere.
*PLEASE DO NOT TRY BOOTING FROM YOUR REAL ROOT AKA '/', EVEN WITH READ ONLY
SET* - Lets make sure the code is bulletproof before we delete your rootfs :)

 --binsh - This flag will boot into simple /bin/sh shell instead of going
through /sbin/init. This is usefull for more complex distribution rootfs
where we have to deal with /etc/fstab and such.

Signed-off-by: Sasha Levin <levinsasha928@gmail.com>
---
 tools/kvm/builtin-run.c |   18 +++++++++++++++++-
 1 files changed, 17 insertions(+), 1 deletions(-)

diff --git a/tools/kvm/builtin-run.c b/tools/kvm/builtin-run.c
index 2e04265..78680ec 100644
--- a/tools/kvm/builtin-run.c
+++ b/tools/kvm/builtin-run.c
@@ -76,11 +76,13 @@ static const char *guest_mac;
 static const char *host_mac;
 static const char *script;
 static const char *guest_name;
+static const char *rootfs;
 static bool single_step;
 static bool readonly_image[MAX_DISK_IMAGES];
 static bool vnc;
 static bool sdl;
 static bool balloon;
+static bool bin_sh;
 extern bool ioport_debug;
 extern int  active_console;
 extern int  debug_iodelay;
@@ -156,6 +158,8 @@ static const struct option options[] = {
 	OPT_BOOLEAN('\0', "balloon", &balloon, "Enable virtio balloon"),
 	OPT_BOOLEAN('\0', "vnc", &vnc, "Enable VNC framebuffer"),
 	OPT_BOOLEAN('\0', "sdl", &sdl, "Enable SDL framebuffer"),
+	OPT_STRING('\0', "rootfs", &rootfs, "path", "Use path as rootfs"),
+	OPT_BOOLEAN('\0', "binsh", &bin_sh, "Boot rootfs to /bin/sh instead of /sbin/init"),
 
 	OPT_GROUP("Kernel options:"),
 	OPT_STRING('k', "kernel", &kernel_filename, "kernel",
@@ -615,7 +619,7 @@ int kvm_cmd_run(int argc, const char **argv, const char *prefix)
 		strlcat(real_cmdline, kernel_cmdline, sizeof(real_cmdline));
 
 	hi = NULL;
-	if (!image_filename[0]) {
+	if (!rootfs && !image_filename[0]) {
 		hi = host_image(real_cmdline, sizeof(real_cmdline));
 		if (hi) {
 			image_filename[0] = hi;
@@ -627,6 +631,18 @@ int kvm_cmd_run(int argc, const char **argv, const char *prefix)
 	if (!strstr(real_cmdline, "root="))
 		strlcat(real_cmdline, " root=/dev/vda rw ", sizeof(real_cmdline));
 
+	if (rootfs) {
+		char tmp[PATH_MAX];
+
+		if (realpath(rootfs, tmp) == 0 ||
+		    virtio_9p__init(kvm, tmp, "/dev/root") < 0)
+			die("Unable to initialize virtio 9p");
+		strcat(real_cmdline, " root=/dev/root rootflags=rw,trans=virtio,version=9p2000.u rootfstype=9p");
+
+		if (bin_sh)
+			strcat(real_cmdline, " init=/bin/sh");
+	}
+
 	if (image_count) {
 		kvm->nr_disks = image_count;
 		kvm->disks    = disk_image__open_all(image_filename, readonly_image, image_count);
-- 
1.7.6