Hi Michael, > On Dec 10, 2016, at 7:28 PM, Michael S. Tsirkin <m...@redhat.com> wrote: > > On Tue, Dec 06, 2016 at 06:15:34PM -0800, Ben Warren wrote: >> Hi Michael, >> >> I’m well on my way to implementing this, but I am really new to the QEMU >> code base and am struggling with some concepts. Please see below: >>> On Oct 5, 2016, at 6:29 PM, Michael S. Tsirkin <m...@redhat.com> wrote: >>> >>> On Tue, Oct 04, 2016 at 03:51:40PM -0700, Ed Swierk wrote: >>>> On Thu, Sep 15, 2016 at 5:36 PM, Michael S. Tsirkin <m...@redhat.com> >>>> wrote: >>>>> On Thu, Sep 15, 2016 at 05:23:28PM -0700, Ed Swierk wrote: >>>>>> I'm wondering what it will take to finish up work on vmgenid. >>>>>> >>>>>> https://lists.gnu.org/archive/html/qemu-devel/2016-01/msg05599.html >>>>> >>>>> We have ACPI_BUILD_TPMLOG_FILE in tree now and I think it could be >>>>> allocated in a similar way. >>>>> Integrate patch "fw-cfg: support writeable blobs" to communicate the >>>>> allocated address back to QEMU. >>>> >>>> Starting with Igor's last version at >>>> https://github.com/imammedo/qemu/commits/vmgen_wip , it's not clear to >>>> me which changes need to be ported, which changes are obsoleted by >>>> your new fw-cfg stuff and/or upstream churn in ACPI, device >>>> properties, etc. In particular ACPI is still a total mystery to me, >>>> though passing a single address from guest to host can't be that hard, >>>> can it? >>>> >>>> Any clues would be appreciated. >>>> >>>> --Ed >>> >>> It might be best to just re-start from the beginning. >>> So the idea is that ACPI should be about supplying the address >>> to guest. To supply address to host we'll use fw cfg. >>> This would be new I think: >>> >>> - add support for writeable fw cfg blobs >> patch applied >>> - add linker/loader command to write address of a blob into >>> such a fw cfg file >>> - add a new file used for vm gen id, use loader command above >>> to pass the address of a blob allocated for it to host >> I don’t really understand the meaning of “file” in this context. It seems >> to be a way of specifying individual fw_cfg entries without explicitly >> giving an index, but is not something that is visible in either the host or >> guest file system. Is this about right? In my code I’m using “/etc/vmgenid” > > yes > >> As for the blob, I’m thinking this is where my main problem is. The >> ‘fw_cfg_add_*()’ functions take a data pointer but doesn’t seem to copy the >> data anywhere. We pass essentially a pointer via ACPI to the guest, so what >> it points to needs to be in an accessible region. I don’t get how to define >> the blob contents. There are command-line ‘fw-cfg’ options where you can >> specify a file, but it’s not clear to me how to use them. Maybe I reserve >> some IO memory or something? > > Not sure I understand the question. fw cfg device will make > memory accessible to guest. Put the guest physical address there. > the address needs to be calculated by linker. > I’m almost ready to submit a V2 of the patch set, but there’s still one issue that I can’t figure out. From the guest, I can read the contents of the blob. If I make a change to the contents of the blob (via QMP) the guest does not see the changes. Is there something I need to do on the QEMU side to “push” the updated fw_cfg contents to the guest? I’ve noticed this both when writing a qtest for the feature, and also in a Linux kernel module I wrote that reads the ACPI contents in a guest.
thanks, Ben
smime.p7s
Description: S/MIME cryptographic signature