On Thu, 2003-05-22 at 19:36, David Wuertele wrote:
> 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?
Are you checking those return values? It that /mnt/msdos/ext2image.bin
path even value when you root FD is the msdos partition?
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