qemu-ga: add guest-sync-delimited

guest-sync leaves it as an exercise to the user as to how to reliably
obtain the response to guest-sync if the client had previously read in a
partial response (due qemu-ga previously being restarted mid-"sentence"
due to reboot, forced restart, etc).

qemu-ga handles this situation on its end by having a client precede
their guest-sync request with a 0xFF byte (invalid UTF-8), which
qemu-ga/QEMU JSON parsers will treat as a flush event. Thus we can
reliably flush the qemu-ga parser state in preparation for receiving
the guest-sync request.

guest-sync-delimited provides the same functionality for a client: when
a guest-sync-delimited is issued, qemu-ga will precede it's response
with a 0xFF byte that the client can use as an indicator to flush its
buffer/parser state in preparation for reliably receiving the
guest-sync-delimited response.

It is also useful as an optimization for clients, since, after issuing a
guest-sync-delimited, clients can safely discard all stale data read
from the channel until the 0xFF is found.

More information available on the wiki:

http://wiki.qemu.org/Features/QAPI/GuestAgent#QEMU_Guest_Agent_Protocol

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>

1 files changed, 0 insertions, 3 deletions

diff --git a/qga/commands-posix.c b/qga/commands-posix.c
index 5b77fa9eee..7b2be2f936 100644
--- a/qga/commands-posix.c
+++ b/qga/commands-posix.c
@@ -35,8 +35,6 @@
 #include "qemu-queue.h"
 #include "host-utils.h"
 
-static GAState *ga_state;
-
 static void reopen_fd_to_null(int fd)
 {
     int nullfd;
@@ -909,7 +907,6 @@ error:
 /* register init/cleanup routines for stateful command groups */
 void ga_command_state_init(GAState *s, GACommandState *cs)
 {
-    ga_state = s;
 #if defined(CONFIG_FSFREEZE)
     ga_command_state_add(cs, guest_fsfreeze_init, guest_fsfreeze_cleanup);
 #endif