[sheepdog] Call to sd_truncate()

[Liu Yuan]

On Thu, Dec 12, 2013 at 01:47:25PM +0100, Hadrien KOHL wrote:
> 2013/12/12 Liu Yuan <namei.unix at gmail.com>
> 
> > On Thu, Dec 12, 2013 at 12:25:52PM +0100, Hadrien KOHL wrote:
> > > I just sent the question to the qemu developer mailing list. But as I
> > did,
> > > I remembered this sd_truncate is also called
> > > from  sd_co_writev(BlockDriverState *bs, int64_t sector_num, int
> > > nb_sectors, QEMUIOVector *qiov):
> > >
> > > static coroutine_fn int sd_co_writev(BlockDriverState *bs, int64_t
> > > sector_num,
> > >                         int nb_sectors, QEMUIOVector *qiov)
> > > {
> > >     SheepdogAIOCB *acb;
> > >      int ret;
> > >
> > >     if (bs->growable && sector_num + nb_sectors > bs->total_sectors) {
> > >         ret = sd_truncate(bs, (sector_num + nb_sectors) *
> > BDRV_SECTOR_SIZE);
> > >         if (ret < 0) {
> > >             return ret;
> > >         }
> >
> > From the code, so if growable is true, seems that sheepdog support
> > automatic
> > grow of volume. So my last email about 'can't resize live VM' is wrong.
> >
> > By a simply glance of the code, seems that bs->growable is set by qcow2.c,
> > which
> > indicate that this might be a feature from qcow2 format.
> >
> > >         bs->total_sectors = sector_num + nb_sectors;
> > >     }
> > >
> > >     acb = sd_aio_setup(bs, qiov, sector_num, nb_sectors);
> > >     acb->aio_done_func = sd_write_done;
> > >     acb->aiocb_type = AIOCB_WRITE_UDATA;
> > >
> > >     ret = sd_co_rw_vector(acb);
> > > ...
> > > }
> > >
> > > This function is mapped to bdrv_co_writev in the qemu driver.
> > > Looking at the test in this function, the only way a shrink could happen
> > -
> > > I guess - is if the units in sector_num and nb_sectors are inconsistent
> > > (esp since there's a conversion to "BDRV_SECTOR_SIZE") in relation to
> > > bs->total_sectors.
> > > I am using qcow2 file format and created the image with qemu-img -t qcow2
> > > create sheepdog:name. Could it be related?
> >
> > I think this might be a bug about running qcow2 in sheepdog, but I can't
> > figure
> > out what is the problem by statically reviewing the code. Is there a
> > reliable
> > way to reproduce it?
> >
> 
> Here is a way to reproduce:
> 
> First I create a test image. Then I boot (here using gentoo live cd).
> 
> # qemu-img create -f qcow2 sheepdog:test 10G
> Formatting 'sheepdog:test', fmt=qcow2 size=10737418240 encryption=off
> cluster_size=65536 lazy_refcounts=off
> # qemu-system-x86_64 -drive
> file=sheepdog:127.0.0.1:7000:test,if=none,id=virtio-disk0,format=qcow2,cache=writeback
> -cdrom /vm/iso/install-amd64-minimal-20131010.iso -boot cd -m 256 -name
> test -vnc 172.16.0.11:0
> 
> Then once logged in the machine via vnc:
> # mkfs.ext4 /dev/vda
> # mkdir /mnt/vda
> 
> Then I start receiving:
> 
> qemu-system-x86_64: shrinking is not supported
> qemu-system-x86_64: shrinking is not supported
> qemu-system-x86_64: shrinking is not supported
> qemu-system-x86_64: shrinking is not supported
> qemu-system-x86_64: shrinking is not supported
> qemu-system-x86_64: shrinking is not supported
> qemu-system-x86_64: shrinking is not supported
> qemu-system-x86_64: shrinking is not supported
> 
> And IO buffer errors on the guest:
> 
> Buffer I/O error on device vda, logical block XXXXXXX
> 
> Hadrien
> 

Just had a test with ubuntu 12.04 live CD following your steps and no problem at
all. I am running latest QEMU, so can you try latest QEMU such as v1.7?

yliu at ubuntu-precise:~/sheepdog$ qemu-img info sheepdog:test
image: sheepdog:test
file format: qcow2
virtual size: 10G (10737418240 bytes)
disk size: 136M
cluster_size: 65536
Format specific information:
    compat: 1.1
    lazy refcounts: false

Thanks
Yuan