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Re: [Qemu-devel] [PATCH v3 2/4] nvdimm acpi: introduce fit buffer

From: Xiao Guangrong
Subject: Re: [Qemu-devel] [PATCH v3 2/4] nvdimm acpi: introduce fit buffer
Date: Wed, 2 Nov 2016 00:00:12 +0800
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.2.0

On 11/01/2016 11:25 PM, Igor Mammedov wrote:
On Tue, 1 Nov 2016 15:17:01 +0000
Stefan Hajnoczi <address@hidden> wrote:

On Sat, Oct 29, 2016 at 12:35:38AM +0800, Xiao Guangrong wrote:
The buffer is used to save the FIT info for all the presented nvdimm
devices which is updated after the nvdimm device is plugged or
unplugged. In the later patch, it will be used to construct NVDIMM
ACPI _FIT method which reflects the presented nvdimm devices after
nvdimm hotplug

As FIT buffer can not completely mapped into guest address space,
OSPM will exit to QEMU multiple times, however, there is the race
condition - FIT may be changed during these multiple exits, so that
some rules are introduced:
1) the user should hold the @lock to access the buffer and

I don't understand the purpose of the QEMUMutex lock.  Don't all threads
calling nvdimm/acpi code hold the QEMU global mutex (main loop and vcpu

-static void nvdimm_build_nfit(GSList *device_list, GArray *table_offsets,
+static void nvdimm_init_fit_buffer(NvdimmFitBuffer *fit_buf)
+    qemu_mutex_init(&fit_buf->lock);
+    fit_buf->fit = g_array_new(false, true /* clear */, 1);

Is it possible to call nvdimm_build_device_structure() here?  That way
we don't duplicate the g_array_new() details.

diff --git a/hw/core/qdev.c b/hw/core/qdev.c
index 5783442..d835e62 100644
--- a/hw/core/qdev.c
+++ b/hw/core/qdev.c
@@ -945,10 +945,21 @@ static void device_set_realized(Object *obj, bool value, 
Error **errp)
                 goto child_realize_fail;
         if (dev->hotplugged) {
         dev->pending_deleted_event = false;
+        dev->realized = value;
+        if (hotplug_ctrl) {
+            hotplug_handler_post_plug(hotplug_ctrl, dev, &local_err);
+        }
+        if (local_err != NULL) {
+            dev->realized = value;

dev->realized = value was already set above.

In order to preserve semantics you would need a bool old_value =
dev->realized which you can restore in post_realize_fail.  QEMU current
does not assign dev->realized = value when there is a failure!


as agreed on
 "Re: [Qemu-devel] [PULL 00/47] virtio, pc: fixes and features" thread
this series would be merged as is and then as follow up author
will fixup all issues with it.

For this patch it means a patch on top of Michael pull req
to drop lock and drop hotplug_handler_post_plug() code in favor
of existing hotplug_handler_plug().

Thank you, Igor, Michael and Stefan. I will do it asap after
this patchset is merged. :)

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