X-Git-Url: http://git.annexia.org/?a=blobdiff_plain;f=virt-what.pod;h=2ef5d08181e7d25ae123aaddc3a433c3109f64ba;hb=fc6413775e8fd011f9583280f30f7c46defa6723;hp=0a724d4b8e3350c4c7574fe61e3c129d7a302f87;hpb=c9622b6019744e7fe13bd8ccd93374abc7770683;p=virt-what.git

diff --git a/virt-what.pod b/virt-what.pod
index 0a724d4..2ef5d08 100644
--- a/virt-what.pod
+++ b/virt-what.pod
@@ -95,7 +95,8 @@ Status: contributed by Justin Clift
 
 The guest is running inside IBM PowerVM Lx86 Linux/x86 emulator.
 
-Status: data supplied by Jeffrey Scheel, not confirmed
+Status: data originally supplied by Jeffrey Scheel, confimed by
+Yufang Zhang and RWMJ
 
 =item B<qemu>
 
@@ -112,6 +113,15 @@ This is a User-Mode Linux (UML) guest.
 
 Status: contributed by Laurent Léonard
 
+=item B<virt>
+
+Some sort of virtualization appears to be present, but we are not sure
+what it is.  In some very rare corner cases where we know that
+virtualization is hard to detect, we will try a timing attack to see
+if certain machine instructions are running much more slowly than they
+should be, which would indicate virtualization.  In this case, the
+generic fact C<virt> is printed.
+
 =item B<virtage>
 
 This is Hitachi Virtualization Manager (HVM) Virtage
@@ -163,6 +173,40 @@ Status: confirmed by RWMJ
 
 =back
 
+=head1 EXIT STATUS
+
+Programs that use or wrap C<virt-what> should check that the exit
+status is 0 before they attempt to parse the output of the command.
+
+A non-zero exit status indicates some error, for example, an
+unrecognized command line argument.  If the exit status is non-zero
+then the output "facts" (if any were printed) cannot be guaranteed and
+should be ignored.
+
+The exit status does I<not> have anything to do with whether the
+program is running on baremetal or under virtualization, nor with
+whether C<virt-what> managed detection "correctly" (which is basically
+unknowable given the large variety of virtualization systems out there
+and that some systems deliberately emulate others).
+
+=head1 RUNNING VIRT-WHAT FROM OTHER PROGRAMS
+
+C<virt-what> is designed so that you can easily run it from
+other programs or wrap it up in a library.
+
+Your program should check the exit status (see the section above).
+
+Some programming languages (notably Python: issue 1652) erroneously
+mask the C<SIGPIPE> signal and do not restore it when executing
+subprocesses.  C<virt-what> is a shell script and some shell commands
+do not work correctly when you do this.  You may see warnings from
+C<virt-what> similar to this:
+
+ echo: write error: Broken pipe
+
+The solution is to set the C<SIGPIPE> signal handler back to C<SIG_DFL>
+before running C<virt-what>.
+
 =head1 IMPORTANT NOTE
 
 Most of the time, using this program is the I<wrong> thing to do.
@@ -185,6 +229,13 @@ tool.
 
 You might include this information in status and monitoring programs.
 
+=item System tuning (sometimes)
+
+You might use this program to tune an operating system so it runs
+better as a virtual machine of a particular hypervisor.  However if
+installing paravirtualized drivers, it's better to check for the
+specific features your drivers need (eg. for the presence of PCI devices).
+
 =back
 
 =head1 SEE ALSO