Automated fsck on boot

[Max Vozeler <max@xxxxxxxxxxxx>]

Hi all,

I'm looking for a user-friendly way to manage automated fsck of
encrypted loop devices during boot. The current way of managing
fscks (losetup -F, fsck, losetup -d, mount) has one big downside
from a usability perspective: It requires the user to enter the
passphrase twice each time the system boots. 

Today I thought of something else that could work, I'm attaching
a quick proof-of-concept patch to describe it. The idea is that we
could do losetup -F, fsck, leave the loop device allocated and have
mount later re-use the loop device. It would require no changes
apart from an optional init script to take care of the fsck.

What do you think about this approach? 

cheers,
Max

-- 
PS: If you are interested, this is one of the last points I want to
solve before integrating loop-AES support into a release version of
Debian installer -- wiki.debian.org/DebianInstaller/PartmanCrypto
The show-stopper bug mentioned is the lack of automated fsck.

--- 2.12r/mount/mount.c~	2006-04-08 16:36:47.000000000 +0200
+++ 2.12r/mount/mount.c	2006-04-08 16:34:19.000000000 +0200
@@ -682,6 +682,10 @@
     if (fake) {
       if (verbose)
 	printf(_("mount: skipping the setup of a loop device\n"));
+    } else if (*loopdev && is_loop_in_use(*loopdev)) {
+      if (verbose)
+	printf(_("mount: skipping the setup of a loop device\n"));
+      *spec = *loopdev;
     } else {
       int loopro = (*flags & MS_RDONLY);
 
--- 2.12r/mount/lomount.h~	2006-04-08 16:36:47.000000000 +0200
+++ 2.12r/mount/lomount.h	2006-04-08 16:24:22.000000000 +0200
@@ -2,6 +2,7 @@
 extern int set_loop(const char *, const char *, int *, const char **, unsigned int *);
 extern int del_loop(const char *);
 extern int is_loop_device(const char *);
+extern int is_loop_in_use(const char *);
 extern char * find_unused_loop_device(void);
 
 extern char *passFDnumber;
--- 2.12r/mount/lomount.c~	2006-04-08 16:36:47.000000000 +0200
+++ 2.12r/mount/lomount.c	2006-04-08 16:25:32.000000000 +0200
@@ -202,6 +202,22 @@
 	return 0;
 }
 
+int is_loop_in_use(const char *dev)
+{
+	int fd;
+	int ret = 0;
+	struct stat statbuf;
+	if (stat (dev, &statbuf) == 0 && S_ISBLK(statbuf.st_mode)) {
+		fd = open (dev, O_RDONLY);
+		if (fd >= 0) {
+			if (is_unused_loop_device(fd) == 0)
+				ret = 1;  /* in use */
+			close(fd);
+		}
+	}
+	return ret;
+}
+
 static int rd_wr_retry(int fd, char *buf, int cnt, int w)
 {
 	int x, y, z;

#!/bin/sh

list_fsck_loops ()
{
	egrep -v '^#' /etc/fstab |
	while read dev mnt fstype opts freq passno; do
		fsck=yes
		loopdev=

		for opt in $(IFS=, && echo $opts); do
			case $opt in
			noauto|sw)
				fsck=no
				;;
			loop=/dev/loop*)
				loopdev=${opt#loop=}
				;;
			esac
		done

		if [ -z "$loopdev" ] || [ "$fsck" = no ]; then
			continue
		fi

		echo $loopdev
	done
}

for dev in $(list_fsck_loops); do
	echo /sbin/losetup -F $dev
	echo distro_specific_fsck_foo $dev
done