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>
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@ -1,5 +1,40 @@
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# *-*- Mode: Python -*-*
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# *-*- Mode: Python -*-*
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##
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#
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# Echo back a unique integer value, and prepend to response a
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# leading sentinel byte (0xFF) the client can check scan for.
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#
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# This is used by clients talking to the guest agent over the
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# wire to ensure the stream is in sync and doesn't contain stale
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# data from previous client. It must be issued upon initial
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# connection, and after any client-side timeouts (including
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# timeouts on receiving a response to this command).
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#
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# After issuing this request, all guest agent responses should be
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# ignored until the response containing the unique integer value
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# the client passed in is returned. Receival of the 0xFF sentinel
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# byte must be handled as an indication that the client's
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# lexer/tokenizer/parser state should be flushed/reset in
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# preparation for reliably receiving the subsequent response. As
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# an optimization, clients may opt to ignore all data until a
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# sentinel value is receiving to avoid unecessary processing of
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# stale data.
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#
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# Similarly, clients should also precede this *request*
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# with a 0xFF byte to make sure the guest agent flushes any
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# partially read JSON data from a previous client connection.
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#
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# @id: randomly generated 64-bit integer
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#
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# Returns: The unique integer id passed in by the client
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#
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# Since: 1.1
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# ##
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{ 'command': 'guest-sync-delimited'
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'data': { 'id': 'int' },
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'returns': 'int' }
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##
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##
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# @guest-sync:
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# @guest-sync:
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#
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#
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@ -13,8 +48,19 @@
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# partially-delivered JSON text in such a way that this response
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# partially-delivered JSON text in such a way that this response
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# can be obtained.
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# can be obtained.
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#
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#
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# In cases where a partial stale response was previously
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# received by the client, this cannot always be done reliably.
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# One particular scenario being if qemu-ga responses are fed
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# character-by-character into a JSON parser. In these situations,
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# using guest-sync-delimited may be optimal.
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#
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# For clients that fetch responses line by line and convert them
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# to JSON objects, guest-sync should be sufficient, but note that
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# in cases where the channel is dirty some attempts at parsing the
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# response may result in a parser error.
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#
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# Such clients should also precede this command
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# Such clients should also precede this command
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# with a 0xFF byte to make such the guest agent flushes any
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# with a 0xFF byte to make sure the guest agent flushes any
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# partially read JSON data from a previous session.
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# partially read JSON data from a previous session.
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#
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#
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# @id: randomly generated 64-bit integer
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# @id: randomly generated 64-bit integer
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27
qemu-ga.c
27
qemu-ga.c
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@ -41,6 +41,7 @@
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#define QGA_VIRTIO_PATH_DEFAULT "\\\\.\\Global\\org.qemu.guest_agent.0"
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#define QGA_VIRTIO_PATH_DEFAULT "\\\\.\\Global\\org.qemu.guest_agent.0"
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#endif
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#endif
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#define QGA_PIDFILE_DEFAULT "/var/run/qemu-ga.pid"
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#define QGA_PIDFILE_DEFAULT "/var/run/qemu-ga.pid"
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#define QGA_SENTINEL_BYTE 0xFF
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struct GAState {
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struct GAState {
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JSONMessageParser parser;
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JSONMessageParser parser;
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@ -54,9 +55,10 @@ struct GAState {
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#ifdef _WIN32
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#ifdef _WIN32
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GAService service;
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GAService service;
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#endif
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#endif
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bool delimit_response;
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};
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};
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static struct GAState *ga_state;
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struct GAState *ga_state;
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#ifdef _WIN32
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#ifdef _WIN32
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DWORD WINAPI service_ctrl_handler(DWORD ctrl, DWORD type, LPVOID data,
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DWORD WINAPI service_ctrl_handler(DWORD ctrl, DWORD type, LPVOID data,
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@ -198,6 +200,11 @@ static void ga_log(const gchar *domain, GLogLevelFlags level,
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}
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}
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}
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}
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void ga_set_response_delimited(GAState *s)
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{
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s->delimit_response = true;
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}
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#ifndef _WIN32
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#ifndef _WIN32
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static void become_daemon(const char *pidfile)
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static void become_daemon(const char *pidfile)
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{
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{
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@ -254,7 +261,7 @@ fail:
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static int send_response(GAState *s, QObject *payload)
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static int send_response(GAState *s, QObject *payload)
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{
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{
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const char *buf;
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const char *buf;
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QString *payload_qstr;
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QString *payload_qstr, *response_qstr;
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GIOStatus status;
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GIOStatus status;
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g_assert(payload && s->channel);
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g_assert(payload && s->channel);
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@ -264,10 +271,20 @@ static int send_response(GAState *s, QObject *payload)
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return -EINVAL;
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return -EINVAL;
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}
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}
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qstring_append_chr(payload_qstr, '\n');
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if (s->delimit_response) {
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buf = qstring_get_str(payload_qstr);
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s->delimit_response = false;
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status = ga_channel_write_all(s->channel, buf, strlen(buf));
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response_qstr = qstring_new();
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qstring_append_chr(response_qstr, QGA_SENTINEL_BYTE);
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qstring_append(response_qstr, qstring_get_str(payload_qstr));
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QDECREF(payload_qstr);
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QDECREF(payload_qstr);
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} else {
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response_qstr = payload_qstr;
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}
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qstring_append_chr(response_qstr, '\n');
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buf = qstring_get_str(response_qstr);
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status = ga_channel_write_all(s->channel, buf, strlen(buf));
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QDECREF(response_qstr);
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if (status != G_IO_STATUS_NORMAL) {
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if (status != G_IO_STATUS_NORMAL) {
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return -EIO;
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return -EIO;
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}
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}
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@ -35,8 +35,6 @@
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#include "qemu-queue.h"
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#include "qemu-queue.h"
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#include "host-utils.h"
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#include "host-utils.h"
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static GAState *ga_state;
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static void reopen_fd_to_null(int fd)
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static void reopen_fd_to_null(int fd)
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{
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{
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int nullfd;
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int nullfd;
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/* register init/cleanup routines for stateful command groups */
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/* register init/cleanup routines for stateful command groups */
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void ga_command_state_init(GAState *s, GACommandState *cs)
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void ga_command_state_init(GAState *s, GACommandState *cs)
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{
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{
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ga_state = s;
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#if defined(CONFIG_FSFREEZE)
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#if defined(CONFIG_FSFREEZE)
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ga_command_state_add(cs, guest_fsfreeze_init, guest_fsfreeze_cleanup);
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ga_command_state_add(cs, guest_fsfreeze_init, guest_fsfreeze_cleanup);
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#endif
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#endif
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va_end(ap);
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va_end(ap);
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}
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}
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int64_t qmp_guest_sync_delimited(int64_t id, Error **errp)
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{
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ga_set_response_delimited(ga_state);
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return id;
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}
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int64_t qmp_guest_sync(int64_t id, Error **errp)
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int64_t qmp_guest_sync(int64_t id, Error **errp)
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{
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{
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return id;
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return id;
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typedef struct GAState GAState;
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typedef struct GAState GAState;
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typedef struct GACommandState GACommandState;
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typedef struct GACommandState GACommandState;
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extern GAState *ga_state;
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void ga_command_state_init(GAState *s, GACommandState *cs);
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void ga_command_state_init(GAState *s, GACommandState *cs);
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void ga_command_state_add(GACommandState *cs,
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void ga_command_state_add(GACommandState *cs,
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void ga_disable_logging(GAState *s);
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void ga_disable_logging(GAState *s);
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void ga_enable_logging(GAState *s);
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void ga_enable_logging(GAState *s);
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void slog(const gchar *fmt, ...);
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void slog(const gchar *fmt, ...);
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void ga_set_response_delimited(GAState *s);
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