> On Jan 16, 2017, at 6:21 AM, Michael S. Tsirkin <m...@redhat.com> wrote: > > On Sat, Jan 14, 2017 at 10:17:53PM -0800, Ben Warren wrote: >> 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 > > fw cfg entities are assumed to be immutable. This week > I'll merge support for writeable fw cfg entries. > I don't see why you want to change fw cfg transparently > though - I think it should be like this > - guest writes GPA into fw cfg > - qemu writes gen id at this GPA > I’ve tried with your patch "fw-cfg-support-writeable-blobs”, setting the ‘read-only’ flag on my blob to false:
fw_cfg_add_file_callback(s, VMGENID_FW_CFG_FILE, NULL, NULL, vms->guid.data, sizeof(vms->guid.data), false); and it doesn’t seem to make a difference. I think we have a misunderstanding here. I’m storing the VM Generation ID __data__ (a GUID) in a fw_cfg blob, not the address. I’ll submit the patch set ASAP so you will understand. > -- > MST regards, Ben
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