* [PATCH doc] Document crosvm memfd server
@ 2020-05-26 17:37 Alyssa Ross
2020-05-27 0:13 ` impaqt
2020-05-27 23:27 ` [PATCH doc v2] " Alyssa Ross
0 siblings, 2 replies; 7+ messages in thread
From: Alyssa Ross @ 2020-05-26 17:37 UTC (permalink / raw)
To: devel; +Cc: Alyssa Ross
---
Looking for another set of eyes on this to check it makes sense to
people who haven't dedicated several weeks of their life to thinking
about it. ;)
developer-manual.adoc | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/developer-manual.adoc b/developer-manual.adoc
index a538437..5a5f80d 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 receives requests for 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
+time with the `--wl-memfd` flag.
+
+
=== Sommelier
https://chromium.googlesource.com/chromiumos/platform2/+/master/vm_tools/sommelier[Sommelier]
--
2.26.2
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH doc] Document crosvm memfd server
2020-05-26 17:37 [PATCH doc] Document crosvm memfd server Alyssa Ross
@ 2020-05-27 0:13 ` impaqt
2020-05-27 23:27 ` [PATCH doc v2] " Alyssa Ross
1 sibling, 0 replies; 7+ messages in thread
From: impaqt @ 2020-05-27 0:13 UTC (permalink / raw)
To: Alyssa Ross, devel
Makes sense to me, but I think there's a typo here:
> +It receives a request consisting of a name and a size, uses those to
> +allocate a receives requests for a
> +https://man7.org/linux/man-pages/man2/memfd_create.2.html[memfd],
"receives requests" is repeated from the previous line.
^ permalink raw reply [flat|nested] 7+ messages in thread
* [PATCH doc v2] Document crosvm memfd server
2020-05-26 17:37 [PATCH doc] Document crosvm memfd server Alyssa Ross
2020-05-27 0:13 ` impaqt
@ 2020-05-27 23:27 ` Alyssa Ross
2020-05-28 0:40 ` impaqt
` (2 more replies)
1 sibling, 3 replies; 7+ messages in thread
From: Alyssa Ross @ 2020-05-27 23:27 UTC (permalink / raw)
To: devel; +Cc: Alyssa Ross, impaqt, Cole Helbling
---
Thanks for the comments. Should be addressed now.
Please take a(nother) look. If you think it looks good, I'd
appreciate a Reviewed-by tag from you. :)
(Last bit is just something nice for me to put in the git log,
e.g. Reviewed-by: Alyssa Ross <hi@alyssa.is>, and means that you had a
look and don't see anything wrong with the changes. By convention
those should be sent by the reviewer rather than just made up by
me. :))
developer-manual.adoc | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff --git a/developer-manual.adoc b/developer-manual.adoc
index a538437..d69707d 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]
--
2.26.2
^ permalink raw reply [flat|nested] 7+ messages in thread* Re: [PATCH doc v2] Document crosvm memfd server
2020-05-27 23:27 ` [PATCH doc v2] " Alyssa Ross
@ 2020-05-28 0:40 ` impaqt
2020-05-29 18:12 ` Alyssa Ross
2020-05-29 18:49 ` Cole Helbling
2020-05-29 18:59 ` Alyssa Ross
2 siblings, 1 reply; 7+ messages in thread
From: impaqt @ 2020-05-28 0:40 UTC (permalink / raw)
To: Alyssa Ross, devel
Looks good. One minor nitpick, take it or leave it:
> +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.
This should be either a comma or parenthesis, not both.
This is just a personal preference of mine, but one I wish were
more widely adopted: when writing markdown I only wrap the "proper
nouns" in `code blocks` for consistency, e.g. "`memfd` server" not
"`memfd server`". But this isn't a hill I'm prepared to die on.
Reviewed-by: impaqt <impaqt@vendek.net>
^^^ Is this what you meant by a tag?
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH doc v2] Document crosvm memfd server
2020-05-27 23:27 ` [PATCH doc v2] " Alyssa Ross
2020-05-28 0:40 ` impaqt
@ 2020-05-29 18:49 ` Cole Helbling
2020-05-29 18:59 ` Alyssa Ross
2 siblings, 0 replies; 7+ messages in thread
From: Cole Helbling @ 2020-05-29 18:49 UTC (permalink / raw)
To: Alyssa Ross, devel; +Cc: Alyssa Ross, impaqt, Cole
On Wed May 27, 2020 at 11:27 PM, Alyssa Ross wrote:
> ---
> Thanks for the comments. Should be addressed now.
>
> Please take a(nother) look. If you think it looks good, I'd
> appreciate a Reviewed-by tag from you. :)
>
> (Last bit is just something nice for me to put in the git log,
> e.g. Reviewed-by: Alyssa Ross <hi@alyssa.is>, and means that you had a
> look and don't see anything wrong with the changes. By convention
> those should be sent by the reviewer rather than just made up by
> me. :))
>
> developer-manual.adoc | 25 +++++++++++++++++++++++++
> 1 file changed, 25 insertions(+)
LGTM. Sorry for the late response!
Reviewed-by: Cole Helbling <cole.e.helbling@outlook.com>
^ permalink raw reply [flat|nested] 7+ messages in thread
* Re: [PATCH doc v2] Document crosvm memfd server
2020-05-27 23:27 ` [PATCH doc v2] " Alyssa Ross
2020-05-28 0:40 ` impaqt
2020-05-29 18:49 ` Cole Helbling
@ 2020-05-29 18:59 ` Alyssa Ross
2 siblings, 0 replies; 7+ messages in thread
From: Alyssa Ross @ 2020-05-29 18:59 UTC (permalink / raw)
To: devel; +Cc: impaqt, Cole Helbling
[-- Attachment #1: Type: text/plain, Size: 121 bytes --]
Committed as fb12866ffe94dda9879d8879dee3043df2d60e7a.
Thank you both. Nice to be starting to get feedback on here. :)
[-- Attachment #2: signature.asc --]
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^ permalink raw reply [flat|nested] 7+ messages in thread
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2020-05-26 17:37 [PATCH doc] Document crosvm memfd server Alyssa Ross
2020-05-27 0:13 ` impaqt
2020-05-27 23:27 ` [PATCH doc v2] " Alyssa Ross
2020-05-28 0:40 ` impaqt
2020-05-29 18:12 ` Alyssa Ross
2020-05-29 18:49 ` Cole Helbling
2020-05-29 18:59 ` Alyssa Ross
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