Re: [PATCH v4] modules: introduce the MODULE_SCMVERSION config

+++ Will McVicker [06/01/21 10:44 -0800]:

Thanks for the vacation notice Jessica! I'm just letting you know I'm
back as well and am happy to respond to any concerns regarding v4 when
you get all caught up.

I hope you had a relaxing holiday :)

Hi Will - thanks, same to you!

On Fri, Dec 18, 2020 at 4:01 AM Jessica Yu [off-list ref] wrote:

quoted

+++ Will McVicker [16/12/20 22:08 +0000]:

quoted

Config MODULE_SCMVERSION introduces a new module attribute --
`scmversion` -- which can be used to identify a given module's SCM
version.  This is very useful for developers that update their kernel
independently from their kernel modules or vice-versa since the SCM
version provided by UTS_RELEASE (`uname -r`) will now differ from the
module's vermagic attribute.

For example, we have a CI setup that tests new kernel changes on the
hikey960 and db845c devices without updating their kernel modules. When
these tests fail, we need to be able to identify the exact device
configuration the test was using. By including MODULE_SCMVERSION, we can
identify the exact kernel and modules' SCM versions for debugging the
failures.

Additionally, by exposing the SCM version via the sysfs node
/sys/module/MODULENAME/scmversion, one can also verify the SCM versions
of the modules loaded from the initramfs. Currently, modinfo can only
retrieve module attributes from the module's ko on disk and not from the
actual module that is loaded in RAM.

You can retrieve the SCM version in two ways,

1) By using modinfo:
   > modinfo -F scmversion MODULENAME
2) By module sysfs node:
   > cat /sys/module/MODULENAME/scmversion

Signed-off-by: Will McVicker <redacted>
---

[ added back diff ]

quoted

quoted

Changelog since v3:
- Dropped [PATCH v2 1/2] scripts/setlocalversion: allow running in a subdir

Documentation/ABI/stable/sysfs-module | 18 ++++++++++++++++++
include/linux/module.h                |  1 +
init/Kconfig                          | 12 ++++++++++++
kernel/module.c                       |  2 ++
scripts/Makefile.modpost              | 22 ++++++++++++++++++++++
scripts/mod/modpost.c                 | 24 +++++++++++++++++++++++-
6 files changed, 78 insertions(+), 1 deletion(-)

diff --git a/Documentation/ABI/stable/sysfs-module b/Documentation/ABI/stable/sysfs-module
index 6272ae5fb366..2ba731767737 100644
--- a/Documentation/ABI/stable/sysfs-module
+++ b/Documentation/ABI/stable/sysfs-module

@@ -32,3 +32,21 @@ Description:

		Note: If the module is built into the kernel, or if the
		CONFIG_MODULE_UNLOAD kernel configuration value is not enabled,
		this file will not be present.
+
+What:		/sys/module/MODULENAME/scmversion
+Date:		November 2020
+KernelVersion:	5.11

I guess we'll have to bump KernelVersion now (sorry about the timing!)

quoted

quoted

+Contact:	Will McVicker [off-list ref]
+Description:	This read-only file will appear if modpost was supplied with an
+		SCM version for the module. It can be enabled with the config
+		MODULE_SCMVERSION. The SCM version is retrieved by
+		scripts/setlocalversion, which means that the presence of this
+		file depends on CONFIG_LOCALVERSION_AUTO=y or LOCALVERSION=.

I think the "or LOCALVERSION=" part is inaccurate, right? We need
just LOCALVERSION_AUTO for the full scm string for this to work.

quoted

quoted

+		When read, the SCM version that the module was compiled with is
+		returned. The SCM version is returned in the following format::
+
+		===
+		Git:		g[a-f0-9]\+(-dirty)\?
+		Mercurial:	hg[a-f0-9]\+(-dirty)\?
+		Subversion:	svn[0-9]\+
+		===

diff --git a/include/linux/module.h b/include/linux/module.h
index c4e7a887f469..6bd710308863 100644
--- a/include/linux/module.h
+++ b/include/linux/module.h

@@ -372,6 +372,7 @@ struct module {

	struct module_attribute *modinfo_attrs;
	const char *version;
	const char *srcversion;
+	const char *scmversion;
	struct kobject *holders_dir;

	/* Exported symbols */

diff --git a/init/Kconfig b/init/Kconfig
index b77c60f8b963..d9ae12f16ba2 100644
--- a/init/Kconfig
+++ b/init/Kconfig

@@ -2131,6 +2131,18 @@ config MODULE_SRCVERSION_ALL

	  the version).  With this option, such a "srcversion" field
	  will be created for all modules.  If unsure, say N.

+config MODULE_SCMVERSION
+	bool "SCM version for modules"
+	depends on LOCALVERSION_AUTO
+	help
+	  This enables the module attribute "scmversion" which can be used
+	  by developers to identify the SCM version of a given module, e.g.
+	  git sha1 or hg sha1. The SCM version can be queried by modinfo or
+	  via the sysfs node: /sys/modules/MODULENAME/scmversion. This is
+	  useful when the kernel or kernel modules are updated separately
+	  since that causes the vermagic of the kernel and the module to
+	  differ.

Since I consider this a debug/developer option, let's add a "If
unsure, say N." at the end of this, similar to the other
module options.

Thanks!

Jessica