Document qemu wrappers.

guestfs.pod

@@ -632,6 +632,30 @@ sort of connection control, when the daemon launches it sends an
 initial word (C<GUESTFS_LAUNCH_FLAG>) which indicates that the guest
 and daemon is alive.  This is what C<guestfs_wait_ready> waits for.
 
+=head1 QEMU WRAPPERS
+
+If you want to compile your own qemu, run qemu from a non-standard
+location, or pass extra arguments to qemu, then you can write a
+shell-script wrapper around qemu.
+
+There is one important rule to remember: you I<must C<exec qemu>> as
+the last command in the shell script (so that qemu replaces the shell
+and becomes the direct child of the libguestfs-using program).  If you
+don't do this, then the qemu process won't be cleaned up correctly.
+
+Here is an example of a wrapper, where I have built my own copy of
+qemu from source:
+
+ #!/bin/sh -
+ qemudir=/home/rjones/d/qemu
+ exec $qemudir/x86_64-softmmu/qemu-system-x86_64 -L $qemudir/pc-bios "$@"
+
+Save this script as C</tmp/qemu.wrapper> (or wherever), C<chmod +x>,
+and then use it by setting the LIBGUESTFS_QEMU environment variable.
+For example:
+
+ LIBGUESTFS_QEMU=/tmp/qemu.wrapper guestfish
+
 =head1 ENVIRONMENT VARIABLES
 
 =over 4
@@ -652,6 +676,8 @@ Set the default qemu binary that libguestfs uses.  If not set, then
 the qemu which was found at compile time by the configure script is
 used.
 
+See also L<QEMU WRAPPERS> above.
+
 =back
 
 =head1 SEE ALSO