[Bug 1215911] Re: wait-for-root fails to wait for plain /dev/sdaX partitions.

[Tetsuo Handa]

I confirmed that below patch fixes my problem.

---------- patch start ----------
--- a/src/wait-for-root.c
+++ b/src/wait-for-root.c
@@ -88,7 +88,9 @@ main (int   argc,
 	/* When the device doesn't exist yet, or is still being processed
 	 * by udev, use the monitor socket to wait it to be done.
 	 */
-	while ((udev_device = udev_monitor_receive_device (udev_monitor)) != NULL) {
+	while (1) {
+		while ((udev_device = udev_monitor_receive_device (udev_monitor)) == NULL)
+			sleep (1);
 		if (matching_device (udev_device, devpath)) {
 			type = udev_device_get_property_value (udev_device, "ID_FS_TYPE");
 			if (type) {
---------- patch end ----------

But why need to handle udev_monitor_receive_device() errors?
I think that wait-for-root.c could be written as short as below code.

---------- simplified wait-for-root.c start ----------
#include <libudev.h>

#include <sys/types.h>
#include <sys/stat.h>

#include <stdio.h>
#include <limits.h>
#include <signal.h>
#include <stdlib.h>
#include <string.h>
#include <unistd.h>

static void alarm_handler(int signum)
{
	exit(1);
}

int main(int argc, char *argv[])
{
	const char *devpath;
	char path[PATH_MAX];
	struct udev *udev;

	if (argc != 3) {
		fprintf(stderr, "Usage: %s DEVICE TIMEOUT\n", argv[0]);
		exit(2);
	}

	devpath = argv[1];
	if (!strncmp(devpath, "UUID=", 5))
		snprintf(path, sizeof(path), "/dev/disk/by-uuid/%s", devpath + 5);
	else if (!strncmp(devpath, "LABEL=", 6))
		snprintf(path, sizeof(path), "/dev/disk/by-label/%s", devpath + 6);
	else
		snprintf(path, sizeof(path), "%s", devpath);

	signal(SIGALRM, alarm_handler);
	alarm(atoi(argv[2]));

	udev = udev_new();
	while (1) {
		struct stat devstat;
		const char *type;
		struct udev_device *udev_device;
		if (stat(path, &devstat) || !S_ISBLK(devstat.st_mode)) {
			sleep(1);
			continue;
		}
		udev_device = udev_device_new_from_devnum(udev, 'b', devstat.st_rdev);
		if (!udev_device) {
			sleep(1);
			continue;
		}
		type = udev_device_get_property_value(udev_device, "ID_FS_TYPE");
		if (type)
			printf("%s\n", type);
		udev_device_unref(udev_device);
		if (type)
			break;
	}
	udev_unref(udev);
	exit(0);
}
---------- simplified wait-for-root.c end ----------

-- 
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https://bugs.launchpad.net/bugs/1215911

Title:
  wait-for-root fails to wait for plain /dev/sdaX partitions.

Status in “initramfs-tools” package in Ubuntu:
  New

Bug description:
  Moving the discussion from http://www.spinics.net/lists/hotplug/msg05769.html
  to launchpad, for I think that this bug needs to be handled in initramfs-tools
  package rather than in udev package.

  ----------

  I'm experiencing random boot failures with wait-for-root utility in Ubuntu
  12.04 ( ubuntu-12.04-server-amd64.iso ) on a HP ProLiant DL360p Gen8 server.

  For example, wait-for-root waited for only 0.13 seconds before giving
  up at

    FSTYPE=$(wait-for-root "${ROOT}" ${ROOTDELAY:-30})

  line in scripts/local in the initramfs, and  immediately enters into

    panic "ALERT!  ${ROOT} does not exist.  Dropping to a shell!"

  line.

  This is a race condition and manually entering "exit" from the panic prompt
  boots the system normally. This is a critical bug for this environment because
  it will randomly fail to perform unattended reboot (e.g. automatic reboot after
  saving kdump).

  ----------

  I examined main() in wait-for-root using debug fprintf() and it turned out that
  udev_monitor_receive_device() is sometimes immediately returning NULL (although
  wait-for-root is using blocking socket).

  I examined udev_monitor_receive_device() in libudev.so.0 using debug fprintf()
  and it turned out that recvmsg() in udev_monitor_receive_device() (which is in
  libudev-monitor.c in udev package) is returning ENOBUFS error before recvmsg()
  returns information of the root partition.

  The wait-for-root utility in initramfs-tools package is not expecting recvmsg()
  to return ENOBUFS error. But since ENOBUFS is an inevitable error, I think that
  wait-for-root (i.e. the caller of udev_monitor_receive_device()) should handle
  this error.

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