[virtio-comment] [PATCH v2 1/3] shared memory: Define shared memory regions

["Dr. David Alan Gilbert (git)" <dgilbert@redhat.com>]

From: "Dr. David Alan Gilbert" <dgilbert@redhat.com>

Define the requirements and idea behind shared memory regions.

Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
---
 content.tex    |  2 ++
 shared-mem.tex | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 35 insertions(+)
 create mode 100644 shared-mem.tex

diff --git a/content.tex b/content.tex
index 836ee52..3dd504c 100644
--- a/content.tex
+++ b/content.tex
@@ -371,6 +371,8 @@ making any more buffers available. When VIRTIO_F_NOTIFICATION_DATA
 has been negotiated, these notifications would then have
 identical \field{next_off} and \field{next_wrap} values.
 
+\input{shared-mem.tex}
+
 \chapter{General Initialization And Device Operation}\label{sec:General Initialization And Device Operation}
 
 We start with an overview of device initialization, then expand on the
diff --git a/shared-mem.tex b/shared-mem.tex
new file mode 100644
index 0000000..85b0c55
--- /dev/null
+++ b/shared-mem.tex
@@ -0,0 +1,33 @@
+\section{Shared Memory Regions}\label{sec:Basic Facilities of a Virtio Device / Shared Memory Regions}
+
+Shared memory regions are an additional facility
+available to devices that need a region of memory that's
+continuously shared between the host and the guest, rather
+than passed between them in the way virtqueue elements are.
+
+Example uses include shared caches and version pools for versioned
+data structures.
+
+The region is chosen by the host and presented to the guest, as
+such it is useful in situations where the memory is accessed on
+the host by other libraries that can't safely access guest RAM.
+
+Shared memory regions MUST NOT be used to control the operation
+of the device, nor to stream data; those should still be performed
+using virtqueues.
+
+A device may have multiple shared memory regions associated with
+it.  Each region has a \field{shmid} to identify it, the meaning
+of which is device-specific.
+
+Enumeration and location of shared memory regions is performed
+using a transport-specific data structure and mechanism.
+
+Memory consistency rules vary depending on the region and the
+device.  Devices MUST define the required behaviour for each
+region.
+
+The guest physical address and the host virtual address MUST NOT
+be used to identify structures within the memory regions; all
+addressing MUST be relative to the start of a particular region.
+
-- 
2.20.1


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