[systemd-devel] [PATCH v2] detect-virt: detect User-Mode Linux

[Ramkumar Ramachandra]

In a User-Mode Linux session:

  $ systemd-detect-virt
  none

Although it is possible to reliably detect virtualization:

  $ cat /proc/cpuinfo
  processor       : 0
  vendor_id       : User Mode Linux
  model name      : UML
  mode            : skas
  host            : Linux kytes 3.11.0-rc1-00009-ge5fd680 (...)
  bogomips        : 7007.43

So, grep for the string "vendor_id\t: User Mode Linux\n" in
/proc/cpuinfo, and say "uml" when asked.

Cc: Lennart Poettering <lennart at poettering.net>
Signed-off-by: Ramkumar Ramachandra <artagnon at gmail.com>
---
 See arch/um/kernel/um_arch.c:75, where it writes the hard-coded
 string "vendor_id\t: User Mode Linux\n".  No variable-width padding,
 so it should be safe to grep for this exact string.

 Also tweaked documentation.

 man/systemd-detect-virt.xml |  1 +
 src/shared/virt.c           | 11 +++++++++++
 2 files changed, 12 insertions(+)

diff --git a/man/systemd-detect-virt.xml b/man/systemd-detect-virt.xml
index 762b6ab..f21493df 100644
--- a/man/systemd-detect-virt.xml
+++ b/man/systemd-detect-virt.xml
@@ -70,6 +70,7 @@
                 <varname>microsoft</varname>,
                 <varname>oracle</varname>, <varname>xen</varname>,
                 <varname>bochs</varname>, <varname>chroot</varname>,
+                <varname>uml</varname>,
                 <varname>openvz</varname>, <varname>lxc</varname>,
                 <varname>lxc-libvirt</varname>,
                 <varname>systemd-nspawn</varname>.</para>
diff --git a/src/shared/virt.c b/src/shared/virt.c
index 1c86a3d..6114b6c 100644
--- a/src/shared/virt.c
+++ b/src/shared/virt.c
@@ -67,6 +67,7 @@ int detect_vm(const char **id) {
         const char *j, *k;
         bool hypervisor;
         _cleanup_free_ char *hvtype = NULL;
+        _cleanup_free_ char *cpuinfo_contents = NULL;
         int r;
 
         /* Try high-level hypervisor sysfs file first:
@@ -164,6 +165,16 @@ int detect_vm(const char **id) {
         }
 
 #endif
+
+        /* Detect User-Mode Linux by reading /proc/cpuinfo */
+        r = read_full_file("/proc/cpuinfo", &cpuinfo_contents, NULL);
+        if (r < 0)
+                return r;
+        if (strstr(cpuinfo_contents, "vendor_id\t: User Mode Linux\n")) {
+                *id = "uml";
+                return 1;
+        }
+
         return 0;
 }
 
-- 
1.8.3.2.736.g869de25