[Qemu-devel] Monitor command pci_add regressed (qdev)

[Markus Armbruster <armbru@redhat.com>]

gdb --args qemu -monitor stdio tmp.qcow2 -S
[...]
QEMU 0.10.50 monitor - type 'help' for more information
(qemu) pci_add pci_addr=auto storage if=virtio,file=foo.img
Program received signal SIGSEGV, Segmentation fault.
0x080630c5 in virtio_blk_init (dev=0x849a008)
    at /home/armbru/work/qemu/hw/virtio-blk.c:368
368         bs->private = dev;

This used to work just fine.

Culprit seems to be commit 07e3af9a.  qdev_init_bdrv() fails, and
virtio_blk_init() doesn't check the failure.

I haven't investigated why qdev_init_bdrv() fails (the old code got the
BlockDriverState just fine).  Regardless, there are scenarios where
qdev_init_bdrv() rightly fails, so virtio_blk_init() needs fixing.

Returning NULL would be easy enough, but its caller
virtio_blk_init_pci() doesn't check its value, and it is a qdev init()
callback, which can't fail.  How to handle the error?  exit(1) would be
just fine for -drive, but not for a monitor command.