balloon: Fix documentation of the --balloon parameter and deprecate it

There are two issues with the documentation of the --balloon parameter:
First, "--balloon none" is simply doing nothing. Even if a machine had a
balloon device by default, this option is not disabling anything, it is
simply ignored. Thus let's simply drop this option from the documentation
to avoid to confuse the users (but keep the code in vl.c for backward
compatibility).
Second, the documentation claims that "--balloon virtio" is the default
mode, but this is not true anymore since commit 382f074371f7dc32a34.
Since that commit, the option also has no real use case anymore, since
you can simply use "--device virtio-balloon" nowadays instead. Thus to
simplify our complex parameter zoo a little bit, let's deprecate the
the parameter now and tell the user to use "--device virtio-balloon"
instead.

Fixes: 382f074371f7dc32a34c944c845b1698e83d8c36
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <1519796303-13257-1-git-send-email-thuth@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

3 files changed, 12 insertions, 7 deletions

diff --git a/qemu-doc.texi b/qemu-doc.texi
index 589519a900..39e38c87ec 100644
--- a/qemu-doc.texi
+++ b/qemu-doc.texi
@@ -2707,6 +2707,11 @@ enabled via the ``-machine usb=on'' argument.
 
 The ``-nodefconfig`` argument is a synonym for ``-no-user-config``.
 
+@subsection -balloon (since 2.12.0)
+
+The @option{--balloon virtio} argument has been superseded by
+@option{--device virtio-balloon}.
+
 @subsection -machine s390-squash-mcss=on|off (since 2.12.0)
 
 The ``s390-squash-mcss=on`` property has been obsoleted by allowing the
diff --git a/qemu-options.hx b/qemu-options.hx
index 2a22a62f74..6585058c6c 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -462,16 +462,13 @@ modprobe i810_audio clocking=48000
 ETEXI
 
 DEF("balloon", HAS_ARG, QEMU_OPTION_balloon,
-    "-balloon none   disable balloon device\n"
     "-balloon virtio[,addr=str]\n"
-    "                enable virtio balloon device (default)\n", QEMU_ARCH_ALL)
+    "                enable virtio balloon device (deprecated)\n", QEMU_ARCH_ALL)
 STEXI
-@item -balloon none
-@findex -balloon
-Disable balloon device.
 @item -balloon virtio[,addr=@var{addr}]
-Enable virtio balloon device (default), optionally with PCI address
-@var{addr}.
+@findex -balloon
+Enable virtio balloon device, optionally with PCI address @var{addr}. This
+option is deprecated, use @option{--device virtio-balloon} instead.
 ETEXI
 
 DEF("device", HAS_ARG, QEMU_OPTION_device,
diff --git a/vl.c b/vl.c
index e648bed0e1..dae986b352 100644
--- a/vl.c
+++ b/vl.c
@@ -2209,6 +2209,9 @@ static int balloon_parse(const char *arg)
 {
     QemuOpts *opts;
 
+    warn_report("This option is deprecated. "
+                "Use '--device virtio-balloon' to enable the balloon device.");
+
     if (strcmp(arg, "none") == 0) {
         return 0;
     }