I don't know how this can hang your system, but instead of doing this:
losetup -o $((512 * 63)) /dev/loop1 /dev/loop0
You could use kpartx:
kpartx -a /dev/loop0
You are going to find in /dev/mapper your loop0p1:
Here you can find an example:
[root@shuVak ~]# dd if=/dev/zero of=caca bs=1024k count=100
100+0 records in
100+0 records out
104857600 bytes (105 MB) copied, 0.656977 seconds, 160 MB/s
[root@shuVak ~]# losetup /dev/loop0 caca
[root@shuVak ~]# fdisk /dev/loop0
Device contains neither a valid DOS partition table, nor Sun, SGI or
OSF disklabel
Building a new DOS disklabel. Changes will remain in memory only,
until you decide to write them. After that, of course, the previous
content won't be recoverable.
Warning: invalid flag 0x0000 of partition table 4 will be corrected by w(rite)
Command (m for help): p
Disk /dev/loop0: 104 MB, 104857600 bytes
255 heads, 63 sectors/track, 12 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
Command (m for help): n
Command action
e extended
p primary partition (1-4)
p
Partition number (1-4): 1
First cylinder (1-12, default 1):
Using default value 1
Last cylinder or +size or +sizeM or +sizeK (1-12, default 12):
Using default value 12
Command (m for help): p
Disk /dev/loop0: 104 MB, 104857600 bytes
255 heads, 63 sectors/track, 12 cylinders
Units = cylinders of 16065 * 512 = 8225280 bytes
Device Boot Start End Blocks Id System
/dev/loop0p1 1 12 96358+ 83 Linux
Command (m for help): t
Selected partition 1
Hex code (type L to list codes): 8e
Changed system type of partition 1 to 8e (Linux LVM)
Command (m for help): w
The partition table has been altered!
Calling ioctl() to re-read partition table.
WARNING: Re-reading the partition table failed with error 22: Invalid argument.
The kernel still uses the old table.
The new table will be used at the next reboot.
Syncing disks.
[root@shuVak ~]# ls /dev/loop*
loop0 loop1 loop2 loop3 loop4 loop5 loop6 loop7
[root@shuVak ~]# kpartx -a /dev/loop0
[root@shuVak ~]# ls /dev/mapper/loop0p1
/dev/mapper/loop0p1
regards,
Jordi
On Fri, Oct 24, 2008 at 3:16 AM, Carlo Wood <carlo@xxxxxxxxxx> wrote:
> Hiya, don't know where else to report this. Please
> correct me if this isn't the right place.
>
> I just ran into a serious bug :((
>
> We were trying to create a virtual filesystem
> in an image (file) of around 238 GB.
>
> Let the files name be foo.img, then we did:
>
> losetup /dev/loop0 foo.img
>
> and then used fdisk /dev/loop0 to create this partition
> table:
>
> uxley:~>fdisk -lu /dev/loop0
>
> Disk /dev/loop0: 238.3 GB, 238370684928 bytes
> 255 heads, 63 sectors/track, 28980 cylinders, total 465567744 sectors
> Units = sectors of 1 * 512 = 512 bytes
>
> Device Boot Start End Blocks Id System
> /dev/loop0p1 * 63 401624 200781 83 Linux
> /dev/loop0p2 401625 16048934 7823655 83 Linux
> /dev/loop0p3 16048935 21928724 2939895 82 Linux swap / Solaris
> /dev/loop0p4 21928725 465563699 221817487+ 5 Extended
> /dev/loop0p5 21928788 27808514 2939863+ 83 Linux
> /dev/loop0p6 27808578 47359619 9775521 83 Linux
> /dev/loop0p7 47359683 57143204 4891761 83 Linux
> /dev/loop0p8 57143268 465563699 204210216 83 Linux
>
> Next we did:
>
> losetup -o $((512 * 63)) /dev/loop1 /dev/loop0
>
> which should make the first partition available under /dev/loop1
> (this certainly works if that partition already contains a fs,
> we then can mount it).
>
> Finally, I wanted to create a filesystem and ran the following
> command:
>
> uxley:~>mke2fs -j -L "/boot" /dev/loop1
> mke2fs 1.40-WIP (14-Nov-2006)
> Filesystem label=/boot
> OS type: Linux
> Block size=4096 (log=2)
> Fragment size=4096 (log=2)
> 29097984 inodes, 58195960 blocks
> 2909798 blocks (5.00%) reserved for the super user
> First data block=0
> Maximum filesystem blocks=0
> 1776 block groups
> 32768 blocks per group, 32768 fragments per group
> 16384 inodes per group
> Superblock backups stored on blocks:
> 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208,
> 4096000, 7962624, 11239424, 20480000, 23887872
>
> Writing inode tables: 306/1776
>
>
> Here the machine completely halted/crashed. I don't know what
> happened, because it's a remote machine.
>
> The writing of the inode table started very fast, but it was
> already slowing down the last few - and completely stopped
> at 306, which was 12 minutes ago (my ssh connection to the
> machine still didn't time out, weird enough).
>
> I can still ping the machine I see.
>
> Note that mke2fs says: 29097984 inodes, 58195960 blocks
> That is 58195960 * 4096 = 238370652160 the full size of
> the image file?!?
>
> This partition is only 200MB though!
>
> Did I do something very stupid, or is this a bug in mke2fs ?
>
> --
> Carlo Wood <carlo@xxxxxxxxxx>
>
> _______________________________________________
> Ext3-users mailing list
> Ext3-users@xxxxxxxxxx
> https://www.redhat.com/mailman/listinfo/ext3-users
>
--
Jordi
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