commit fb12866ffe94dda9879d8879dee3043df2d60e7a (patch)
parent 66beee3 HTTPS Creative Commons link
tree 14f15baae8ac069ea08875c7cb7da35539fb79da
author Alyssa Ross <hi@alyssa.is> 2020-05-26 17:32:17 +0000
committer Alyssa Ross <hi@alyssa.is> 2020-05-29 18:56:36 +0000
Document crosvm memfd server
Reviewed-by: impaqt <impaqt@vendek.net>
Reviewed-by: Cole Helbling <cole.e.helbling@outlook.com>
---
developer-manual.adoc | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/developer-manual.adoc b/developer-manual.adoc
index a538437..b7eb2cb 100644
--- a/developer-manual.adoc
+++ b/developer-manual.adoc
@@ -194,6 +194,31 @@ compile the policy files into the crosvm binary so paths don't have to
be hardcoded.
+==== The memfd server
+
+Spectrum's crosvm has been augmented with a feature called the "`memfd
+server`" (currently only on the
+https://spectrum-os.org/git/crosvm/log/?h=interguest[interguest]
+branch). This is a small server that listens on a Unix stream socket.
+It receives a request consisting of a name and a size, uses those to
+allocate a
+https://man7.org/linux/man-pages/man2/memfd_create.2.html[memfd], and
+then sends the resulting memfd file descriptor back over the socket in
+response, along with a single byte status code.
+
+The purpose of this is that it can be exposed to the guest over
+virtio_wl. This means that the guest can request and receive
+allocations of host memory. This is important, because virtio_wl only
+allows file descriptors pointing to host memory to be sent over
+virtio_wl -- a memfd allocated in a guest cannot be sent over virtio_wl.
+It is rare that a guest needs to be able to allocate and send shared
+memory in this way, but it is important for a Wayland compositor
+running in a guest to be able to do this.
+
+The memfd server is disabled by default, but is enabled at startup
+with the `--wl-memfd` flag.
+
+
=== Sommelier
https://chromium.googlesource.com/chromiumos/platform2/+/master/vm_tools/sommelier[Sommelier]
glossary
--------
Commit objects reference one tree, and zero or more parents.
Single parent commits can typically generate a patch in
unified diff format via `git format-patch'.
Multiple parents means the commit is a merge.
Root commits have no ancestor. Note that it is
possible to have multiple root commits when merging independent histories.
Every commit references one top-level tree object.
git clone https://inbox.spectrum-os.org/doc