On Wed, Mar 30, 2011 at 9:15 AM, Conor Murphy
conor_murphy_v...@hotmail.com wrote:
I'm trying to write a virtio-blk driver for Solaris. I've gotten it to the
point
where Solaris can see the device and create a ZFS file system on it.
However when I try and create a UFS filesystem on the device, the VM crashed
with the error
*** glibc detected *** /usr/bin/qemu-kvm: double free or corruption (!prev):
0x7f2d38000a00 ***
This is a bug in QEMU. A guest must not be able to trigger a crash.
I can reproduce the problem with a simple dd, i.e.
dd if=/dev/zero of=/dev/rdsk/c2d10p0 bs=5000 count=1
I think this a raw character device, which is why you're even able to
perform non-blocksize accesses? Have you looked at how other drivers
(like the Xen pv blkfront) handle this?
My driver will create a virtio-blk request with two elements in the sg list,
one
for the first 4096 byes and the other for the remaining 904.
From stepping through with gdb, virtio_blk_handle_write will sets n_sectors
to 9
(5000 / 512). Later on the code, n_sectors is used the calculate the size of
the
buffer required but 9 * 512 is too small and so when the request is process it
ends up writing past the end of the buffer and I guest this triggers the glibc
error.
We need to validate that (qiov-size % BDRV_SECTOR_SIZE) == 0 and
reject invalid requests.
Is there a requirement for virtio-blk guest drivers that all i/o requests are
sized in multiples of 512 bytes?
There is no strict requirement according to the virtio specification,
but maybe there should be:
http://ozlabs.org/~rusty/virtio-spec/virtio-spec-0.8.9.pdf
Stefan
