diff mbox

[V4] kvm tool: Use the root partition of the host to boot the guest machine

Message ID 1303223344-3515-1-git-send-email-prasadjoshi124@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Prasad Joshi April 19, 2011, 2:29 p.m. UTC
The kvm run command should automatically pickup the image file to boot if one is
not explicitly specified.

Changes since V1:
 - Deallocate variable 'line' when fopen(/proc/mounts) fails

Changes since V2:
 - Instead of searching from /proc/mounts, use the device file /dev/root to
  detect the device file for root file system
 - Added a helper function get_host_image() to return the image to be used to
  boot the virtual machine.

Changes since V3:
 - The link '/dev/root' might be missing on some of the systems. Switched back
   to using /proc/mounts file.
 - Some simple reformatting

Signed-off-by: Prasad Joshi <prasadjoshi124@gmail.com>
---
 tools/kvm/kvm-run.c |  109 +++++++++++++++++++++++++++++++++++++++++++++-----
 1 files changed, 98 insertions(+), 11 deletions(-)

Comments

Ingo Molnar April 19, 2011, 2:38 p.m. UTC | #1
* Prasad Joshi <prasadjoshi124@gmail.com> wrote:

> The kvm run command should automatically pickup the image file to boot if one is
> not explicitly specified.
> 
> Changes since V1:
>  - Deallocate variable 'line' when fopen(/proc/mounts) fails
> 
> Changes since V2:
>  - Instead of searching from /proc/mounts, use the device file /dev/root to
>   detect the device file for root file system
>  - Added a helper function get_host_image() to return the image to be used to
>   boot the virtual machine.
> 
> Changes since V3:
>  - The link '/dev/root' might be missing on some of the systems. Switched back
>    to using /proc/mounts file.
>  - Some simple reformatting
> 
> Signed-off-by: Prasad Joshi <prasadjoshi124@gmail.com>
> ---
>  tools/kvm/kvm-run.c |  109 +++++++++++++++++++++++++++++++++++++++++++++-----
>  1 files changed, 98 insertions(+), 11 deletions(-)

Looks good here, with your patch applied 'kvm run' will now boot host userspace 
with zero configuration needed (!), when there's a bzImage built in that kernel 
tree:

  aldebaran:~/linux/linux/tools/kvm> ./kvm run

  [...]

  Welcome to Fedora release 16 (Rawhide)!

Tested-by: Ingo Molnar <mingo@elte.hu>

I noticed two quirks:

1)

i mentioned this earlier, 'kvm run' will display a lengthy help screen or will 
just run the bzImage - depending on whether the file is present. Assymetric 
tool behavior like that is not very consistent - i'd suggest to print an 
intermediate help screen instead:

   ./kvm run

   No kernel image found - please see 'kvm run --help' for more options

This informs the user of two things: a) that it tried to find a kernel image 
but failed to find it b) how to get the larger help text.

2)

I get this:

 Warning: Unable to open /dev/net/tun

This is a meaningless error message to the user. What is a '/dev/net/tun' and 
why does the user care? A much better error message would be something like:

 Info: Tried to activate transparent guest networking but was unable to open /dev/net/tun
       See "kvm run --help" about networking setup details.

Thanks,

	Ingo
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diff mbox

Patch

diff --git a/tools/kvm/kvm-run.c b/tools/kvm/kvm-run.c
index 17fef20..c3da21f 100644
--- a/tools/kvm/kvm-run.c
+++ b/tools/kvm/kvm-run.c
@@ -9,6 +9,7 @@ 
 #include <sys/utsname.h>
 #include <sys/types.h>
 #include <sys/stat.h>
+#include <ctype.h>
 
 /* user defined header files */
 #include <linux/types.h>
@@ -214,12 +215,91 @@  static const char *find_kernel(void)
 	return NULL;
 }
 
+static int root_device(char *dev, long *part)
+{
+	FILE   *fp;
+	char   *line;
+	int    tmp;
+	size_t nr_read;
+	char   device[PATH_MAX];
+	char   mnt_pt[PATH_MAX];
+	char   resolved_path[PATH_MAX];
+	char   *p;
+	struct stat st;
+
+	fp = fopen("/proc/mounts", "r");
+	if (!fp)
+		return -1;
+
+	line = NULL;
+	tmp  = 0;
+	while (!feof(fp)) {
+		if (getline(&line, &nr_read, fp) < 0)
+			break;
+		sscanf(line, "%s %s", device, mnt_pt);
+		if (!strncmp(device, "/dev", 4) && !strcmp(mnt_pt, "/")) {
+			tmp = 1;
+			break;
+		}
+	}
+	fclose(fp);
+	free(line);
+
+	if (!tmp)
+		return -1;
+
+	/* get the absolute path */
+	if (!realpath(device, resolved_path))
+		return -1;
+
+	/* find the partition number */
+	p = resolved_path;
+	while (*p) {
+		if (isdigit(*p)) {
+			strncpy(dev, resolved_path, p - resolved_path);
+			*part = atol(p);
+			break;
+		}
+		p++;
+	}
+
+	/* verify the device path */
+	if (stat(dev, &st) < 0)
+		return -1;
+	return 0;
+}
+
+static char *host_image(char *cmd_line, size_t size)
+{
+	char *t;
+	char device[PATH_MAX];
+	long part = 0;
+
+	t = malloc(PATH_MAX);
+	if (!t)
+		return NULL;
+
+	/* check for the root file system */
+	if (root_device(device, &part) < 0) {
+		free(t);
+		return NULL;
+	}
+	strncpy(t, device, PATH_MAX);
+	if (!strstr(cmd_line, "root=")) {
+		char tmp[PATH_MAX];
+		snprintf(tmp, sizeof(tmp), "root=/dev/vda%ld rw ", part);
+		strlcat(cmd_line, tmp, size);
+	}
+	return t;
+}
+
 int kvm_cmd_run(int argc, const char **argv, const char *prefix)
 {
 	static char real_cmdline[2048];
 	int exit_code = 0;
 	int i;
 	struct virtio_net_parameters net_params;
+	char *hi;
 
 	signal(SIGALRM, handle_sigalrm);
 	signal(SIGQUIT, handle_sigquit);
@@ -288,22 +368,29 @@  int kvm_cmd_run(int argc, const char **argv, const char *prefix)
 
 	kvm = kvm__init(kvm_dev, ram_size);
 
+	memset(real_cmdline, 0, sizeof(real_cmdline));
+	strcpy(real_cmdline, "notsc nolapic noacpi pci=conf1 console=ttyS0 ");
+	if (kernel_cmdline)
+		strlcat(real_cmdline, kernel_cmdline, sizeof(real_cmdline));
+
+	hi = NULL;
+	if (!image_filename) {
+		hi = host_image(real_cmdline, sizeof(real_cmdline));
+		if (hi) {
+			image_filename = hi;
+			readonly_image = true;
+		}
+	}
+
+	if (!strstr(real_cmdline, "root="))
+		strlcat(real_cmdline, "root=/dev/vda rw ", sizeof(real_cmdline));
+
 	if (image_filename) {
 		kvm->disk_image	= disk_image__open(image_filename, readonly_image);
 		if (!kvm->disk_image)
 			die("unable to load disk image %s", image_filename);
 	}
-
-	strcpy(real_cmdline, "notsc nolapic noacpi pci=conf1 console=ttyS0 ");
-	if (!kernel_cmdline || !strstr(kernel_cmdline, "root=")) {
-		strlcat(real_cmdline, "root=/dev/vda rw ",
-				sizeof(real_cmdline));
-	}
-
-	if (kernel_cmdline) {
-		strlcat(real_cmdline, kernel_cmdline, sizeof(real_cmdline));
-		real_cmdline[sizeof(real_cmdline)-1] = '\0';
-	}
+	free(hi);
 
 	if (!kvm__load_kernel(kvm, kernel_filename, initrd_filename,
 				real_cmdline))