I have an EXT2 filesystem on a file that can be read loopback
sometimes, but not others!
I have a box with a root fs on ext2, and another (small) root fs on
msdos. When I boot my box onto the ext2 partition, and run the
following:
# mount /dev/ide/host0/bus0/target0/lun0/p1 /mnt/msdos
# losetup /dev/loop/0 /mnt/msdos/ext2image.bin
# mount /dev/loop/0 /mnt/e2fs
...this results in the ext2 filesystem image being mounted fine. I
can chdir into /mnt/e2fs and read and write fine.
But when I boot into the msdos partition, and execute the following:
ffd = open ("/mnt/msdos/ext2image.bin", O_RDWR);
fd = open ("/dev/loop/0", O_RDWR);
memset (&loopinfo, 0, sizeof(loopinfo));
strncpy (loopinfo.lo_name, "/mnt/msdos/ext2image.bin", LO_NAME_SIZE);
namesize = strlen ("/mnt/msdos/ext2image.bin");
loopinfo.lo_name[namesize];
loopinfo.lo_offset = 0;
loopinfo.lo_encrypt_type = LO_CRYPT_NONE;
loopinfo.lo_encrypt_key_size = 0;
ioctl (fd, LOOP_SET_FD, ffd);
ioctl (fd, LOOP_SET_STATUS, &loopinfo);
close (fd);
close (ffd);
mount ("/dev/loop/0", "/mnt", "ext2", 0, NULL);
chdir ("/mnt");
This results in the following kernel error:
EXT2-fs: unable to read superblock
How is this possible? Why would the exact same file mounted on the
exact same loopback device have a readable superblock in the first
instance, but an unreadable one in the second?
The only difference is which root fs I booted into. The loopback
commands should be the same. Any clues?
Thanks,
Dave
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