Bug 1000428

Doh.  We fixed the same problem in virt-make-fs too ...

(In reply to Gerd Hoffmann from comment #0)
> While being at it: Having a --label=<text> cmd line switch (to specify a
> volume label for the filesystem) would be great too.  Wanna have a separate
> RFE bug for this?

Don't worry, I'll fix them both.

Fixed upstream in the following commits:

https://github.com/libguestfs/libguestfs/commit/d432ab2b5a965110bab542bfd397785eee9753dd
https://github.com/libguestfs/libguestfs/commit/c46e41cb3c41f6283e0350cac6ef0b9178ed3941
https://github.com/libguestfs/libguestfs/commit/e17cd73fb7e3d7ce5e28f51c8451033f48a39153
https://github.com/libguestfs/libguestfs/commit/a75ca610b80614253f8a9d9828a97dc61d919b8a

Can reproduce with libguestfs-tools-c-1.22.5-3.el7.x86_64

Steps to reproduce:
1. qemu-img create -f qcow2 test.img 100M
2. virt-format --add test.img --format=qcow2 --partition=mbr --filesystem=vfat
3. attach image as usb disk to windows guest

Result:
usbstick doesn't show up in Windows Explorer

(In reply to Lingfei Kong from comment #4)
> Can reproduce with libguestfs-tools-c-1.22.5-3.el7.x86_64
> 
> Steps to reproduce:
> 1. qemu-img create -f qcow2 test.img 100M
> 2. virt-format --add test.img --format=qcow2 --partition=mbr
> --filesystem=vfat
> 3. attach image as usb disk to windows guest

When attaching the image, did you ensure the format is set
to qcow2?  If you set it to raw then Windows would just see
a qcow2 header, everything would be completely broken.

> Result:
> usbstick doesn't show up in Windows Explorer

Can you run:

virt-filesystems -a test.img --all --long -h

The output should show that the MBR byte is set to 0b.
For examples see:
https://github.com/libguestfs/libguestfs/commit/d432ab2b5a965110bab542bfd397785eee9753dd

(In reply to Richard W.M. Jones from comment #5)

> When attaching the image, did you ensure the format is set
> to qcow2?  If you set it to raw then Windows would just see
> a qcow2 header, everything would be completely broken.

Yes, I specified the format as qcow2 in the steps showed in commnet #4, here is the command I used to attach the image file:
/usr/libexec/qemu-kvm -m 1024 -name "VM" -drive file=/root/win.img -usbdevice disk:format=qcow2:/test.img

> Can you run:
> 
> virt-filesystems -a test.img --all --long -h
> 
> The output should show that the MBR byte is set to 0b.

I checked the image file(showed in comment #4, it is created with command: virt-format --add test.img --format=qcow2 --partition=mbr --filesystem=vfat
) with virt-filesystems  tool, the following is the output:
[host]#virt-filesystems -a test.img --all --long -h
Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1  filesystem  vfat  -      -    100M  -
/dev/sda1  partition   -     -      83   100M  /dev/sda
/dev/sda   device      -     -      -    100M  -

It shows the MBR byte is 83 not 0b.

I'm just reading back more closely.  It looks like you have
correctly reproduced the original problem with 1.22.5.

The bug should be fixed in libguestfs >= 1.22.6-5.el7.

Verified it with libguestfs-1.22.6-15.el7

Steps to verify: 
1. #qemu-img create -f qcow2 test.img 100M

2. #virt-format --add test.img --format=qcow2 --partition=mbr --filesystem=vfat

3. attach image as usb disk to windows guest
#/usr/libexec/qemu-kvm -m 1024 -name "VM" -drive file=/var/lib/libvirt/images/vm1.img -usbdevice disk:format=qcow2:/root/lkong/test.img -vnc :0

4.
 # virt-filesystems -a test.img --all --long -h
Name       Type        VFS   Label  MBR  Size  Parent
/dev/sda1  filesystem  vfat  -      -    100M  -
/dev/sda1  partition   -     -      0b   100M  /dev/sda
/dev/sda   device      -     -      -    100M  -


Result:
1. usbstick shows up in Windows Explorer.
2. It shows the MBR byte is 0b in step 4. 

So, this bug is fixed.

This request was resolved in Red Hat Enterprise Linux 7.0.

Contact your manager or support representative in case you have further questions about the request.