diff options
Diffstat (limited to 'docs')
| -rw-r--r-- | docs/qmp/README | 88 | ||||
| -rw-r--r-- | docs/qmp/qmp-events.txt | 502 | ||||
| -rw-r--r-- | docs/qmp/qmp-spec.txt | 282 |
3 files changed, 872 insertions, 0 deletions
diff --git a/docs/qmp/README b/docs/qmp/README new file mode 100644 index 0000000000..c95a08c234 --- /dev/null +++ b/docs/qmp/README @@ -0,0 +1,88 @@ + QEMU Monitor Protocol + ===================== + +Introduction +------------- + +The QEMU Monitor Protocol (QMP) allows applications to communicate with +QEMU's Monitor. + +QMP is JSON[1] based and currently has the following features: + +- Lightweight, text-based, easy to parse data format +- Asynchronous messages support (ie. events) +- Capabilities Negotiation + +For detailed information on QMP's usage, please, refer to the following files: + +o qmp-spec.txt QEMU Monitor Protocol current specification +o qmp-commands.txt QMP supported commands (auto-generated at build-time) +o qmp-events.txt List of available asynchronous events + +There is also a simple Python script called 'qmp-shell' available. + +IMPORTANT: It's strongly recommended to read the 'Stability Considerations' +section in the qmp-commands.txt file before making any serious use of QMP. + + +[1] http://www.json.org + +Usage +----- + +To enable QMP, you need a QEMU monitor instance in "control mode". There are +two ways of doing this. + +The simplest one is using the '-qmp' command-line option. The following +example makes QMP available on localhost port 4444: + + $ qemu [...] -qmp tcp:localhost:4444,server + +However, in order to have more complex combinations, like multiple monitors, +the '-mon' command-line option should be used along with the '-chardev' one. +For instance, the following example creates one user monitor on stdio and one +QMP monitor on localhost port 4444. + + $ qemu [...] -chardev stdio,id=mon0 -mon chardev=mon0,mode=readline \ + -chardev socket,id=mon1,host=localhost,port=4444,server \ + -mon chardev=mon1,mode=control + +Please, refer to QEMU's manpage for more information. + +Simple Testing +-------------- + +To manually test QMP one can connect with telnet and issue commands by hand: + +$ telnet localhost 4444 +Trying 127.0.0.1... +Connected to localhost. +Escape character is '^]'. +{"QMP": {"version": {"qemu": {"micro": 50, "minor": 13, "major": 0}, "package": ""}, "capabilities": []}} +{ "execute": "qmp_capabilities" } +{"return": {}} +{ "execute": "query-version" } +{"return": {"qemu": {"micro": 50, "minor": 13, "major": 0}, "package": ""}} + +Development Process +------------------- + +When changing QMP's interface (by adding new commands, events or modifying +existing ones) it's mandatory to update the relevant documentation, which is +one (or more) of the files listed in the 'Introduction' section*. + +Also, it's strongly recommended to send the documentation patch first, before +doing any code change. This is so because: + + 1. Avoids the code dictating the interface + + 2. Review can improve your interface. Letting that happen before + you implement it can save you work. + +* The qmp-commands.txt file is generated from the qmp-commands.hx one, which + is the file that should be edited. + +Homepage +-------- + +http://wiki.qemu.org/QMP diff --git a/docs/qmp/qmp-events.txt b/docs/qmp/qmp-events.txt new file mode 100644 index 0000000000..4b24ec900d --- /dev/null +++ b/docs/qmp/qmp-events.txt @@ -0,0 +1,502 @@ + QEMU Monitor Protocol Events + ============================ + +BALLOON_CHANGE +-------------- + +Emitted when the guest changes the actual BALLOON level. This +value is equivalent to the 'actual' field return by the +'query-balloon' command + +Data: + +- "actual": actual level of the guest memory balloon in bytes (json-number) + +Example: + +{ "event": "BALLOON_CHANGE", + "data": { "actual": 944766976 }, + "timestamp": { "seconds": 1267020223, "microseconds": 435656 } } + +BLOCK_IMAGE_CORRUPTED +--------------------- + +Emitted when a disk image is being marked corrupt. + +Data: + +- "device": Device name (json-string) +- "msg": Informative message (e.g., reason for the corruption) (json-string) +- "offset": If the corruption resulted from an image access, this is the access + offset into the image (json-int) +- "size": If the corruption resulted from an image access, this is the access + size (json-int) + +Example: + +{ "event": "BLOCK_IMAGE_CORRUPTED", + "data": { "device": "ide0-hd0", + "msg": "Prevented active L1 table overwrite", "offset": 196608, + "size": 65536 }, + "timestamp": { "seconds": 1378126126, "microseconds": 966463 } } + +BLOCK_IO_ERROR +-------------- + +Emitted when a disk I/O error occurs. + +Data: + +- "device": device name (json-string) +- "operation": I/O operation (json-string, "read" or "write") +- "action": action that has been taken, it's one of the following (json-string): + "ignore": error has been ignored + "report": error has been reported to the device + "stop": error caused VM to be stopped + +Example: + +{ "event": "BLOCK_IO_ERROR", + "data": { "device": "ide0-hd1", + "operation": "write", + "action": "stop" }, + "timestamp": { "seconds": 1265044230, "microseconds": 450486 } } + +Note: If action is "stop", a STOP event will eventually follow the +BLOCK_IO_ERROR event. + +BLOCK_JOB_CANCELLED +------------------- + +Emitted when a block job has been cancelled. + +Data: + +- "type": Job type (json-string; "stream" for image streaming + "commit" for block commit) +- "device": Device name (json-string) +- "len": Maximum progress value (json-int) +- "offset": Current progress value (json-int) + On success this is equal to len. + On failure this is less than len. +- "speed": Rate limit, bytes per second (json-int) + +Example: + +{ "event": "BLOCK_JOB_CANCELLED", + "data": { "type": "stream", "device": "virtio-disk0", + "len": 10737418240, "offset": 134217728, + "speed": 0 }, + "timestamp": { "seconds": 1267061043, "microseconds": 959568 } } + +BLOCK_JOB_COMPLETED +------------------- + +Emitted when a block job has completed. + +Data: + +- "type": Job type (json-string; "stream" for image streaming + "commit" for block commit) +- "device": Device name (json-string) +- "len": Maximum progress value (json-int) +- "offset": Current progress value (json-int) + On success this is equal to len. + On failure this is less than len. +- "speed": Rate limit, bytes per second (json-int) +- "error": Error message (json-string, optional) + Only present on failure. This field contains a human-readable + error message. There are no semantics other than that streaming + has failed and clients should not try to interpret the error + string. + +Example: + +{ "event": "BLOCK_JOB_COMPLETED", + "data": { "type": "stream", "device": "virtio-disk0", + "len": 10737418240, "offset": 10737418240, + "speed": 0 }, + "timestamp": { "seconds": 1267061043, "microseconds": 959568 } } + +BLOCK_JOB_ERROR +--------------- + +Emitted when a block job encounters an error. + +Data: + +- "device": device name (json-string) +- "operation": I/O operation (json-string, "read" or "write") +- "action": action that has been taken, it's one of the following (json-string): + "ignore": error has been ignored, the job may fail later + "report": error will be reported and the job canceled + "stop": error caused job to be paused + +Example: + +{ "event": "BLOCK_JOB_ERROR", + "data": { "device": "ide0-hd1", + "operation": "write", + "action": "stop" }, + "timestamp": { "seconds": 1265044230, "microseconds": 450486 } } + +BLOCK_JOB_READY +--------------- + +Emitted when a block job is ready to complete. + +Data: + +- "device": device name (json-string) + +Example: + +{ "event": "BLOCK_JOB_READY", + "data": { "device": "ide0-hd1" }, + "timestamp": { "seconds": 1265044230, "microseconds": 450486 } } + +Note: The "ready to complete" status is always reset by a BLOCK_JOB_ERROR +event. + +DEVICE_DELETED +----------------- + +Emitted whenever the device removal completion is acknowledged +by the guest. +At this point, it's safe to reuse the specified device ID. +Device removal can be initiated by the guest or by HMP/QMP commands. + +Data: + +- "device": device name (json-string, optional) +- "path": device path (json-string) + +{ "event": "DEVICE_DELETED", + "data": { "device": "virtio-net-pci-0", + "path": "/machine/peripheral/virtio-net-pci-0" }, + "timestamp": { "seconds": 1265044230, "microseconds": 450486 } } + +DEVICE_TRAY_MOVED +----------------- + +It's emitted whenever the tray of a removable device is moved by the guest +or by HMP/QMP commands. + +Data: + +- "device": device name (json-string) +- "tray-open": true if the tray has been opened or false if it has been closed + (json-bool) + +{ "event": "DEVICE_TRAY_MOVED", + "data": { "device": "ide1-cd0", + "tray-open": true + }, + "timestamp": { "seconds": 1265044230, "microseconds": 450486 } } + +NIC_RX_FILTER_CHANGED +----------------- + +The event is emitted once until the query command is executed, +the first event will always be emitted. + +Data: + +- "name": net client name (json-string) +- "path": device path (json-string) + +{ "event": "NIC_RX_FILTER_CHANGED", + "data": { "name": "vnet0", + "path": "/machine/peripheral/vnet0/virtio-backend" }, + "timestamp": { "seconds": 1368697518, "microseconds": 326866 } } +} + +RESET +----- + +Emitted when the Virtual Machine is reseted. + +Data: None. + +Example: + +{ "event": "RESET", + "timestamp": { "seconds": 1267041653, "microseconds": 9518 } } + +RESUME +------ + +Emitted when the Virtual Machine resumes execution. + +Data: None. + +Example: + +{ "event": "RESUME", + "timestamp": { "seconds": 1271770767, "microseconds": 582542 } } + +RTC_CHANGE +---------- + +Emitted when the guest changes the RTC time. + +Data: + +- "offset": Offset between base RTC clock (as specified by -rtc base), and +new RTC clock value (json-number) + +Example: + +{ "event": "RTC_CHANGE", + "data": { "offset": 78 }, + "timestamp": { "seconds": 1267020223, "microseconds": 435656 } } + +SHUTDOWN +-------- + +Emitted when the Virtual Machine is powered down. + +Data: None. + +Example: + +{ "event": "SHUTDOWN", + "timestamp": { "seconds": 1267040730, "microseconds": 682951 } } + +Note: If the command-line option "-no-shutdown" has been specified, a STOP +event will eventually follow the SHUTDOWN event. + +SPICE_CONNECTED, SPICE_DISCONNECTED +----------------------------------- + +Emitted when a SPICE client connects or disconnects. + +Data: + +- "server": Server information (json-object) + - "host": IP address (json-string) + - "port": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") +- "client": Client information (json-object) + - "host": IP address (json-string) + - "port": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + +Example: + +{ "timestamp": {"seconds": 1290688046, "microseconds": 388707}, + "event": "SPICE_CONNECTED", + "data": { + "server": { "port": "5920", "family": "ipv4", "host": "127.0.0.1"}, + "client": {"port": "52873", "family": "ipv4", "host": "127.0.0.1"} +}} + +SPICE_INITIALIZED +----------------- + +Emitted after initial handshake and authentication takes place (if any) +and the SPICE channel is up'n'running + +Data: + +- "server": Server information (json-object) + - "host": IP address (json-string) + - "port": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + - "auth": authentication method (json-string, optional) +- "client": Client information (json-object) + - "host": IP address (json-string) + - "port": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + - "connection-id": spice connection id. All channels with the same id + belong to the same spice session (json-int) + - "channel-type": channel type. "1" is the main control channel, filter for + this one if you want track spice sessions only (json-int) + - "channel-id": channel id. Usually "0", might be different needed when + multiple channels of the same type exist, such as multiple + display channels in a multihead setup (json-int) + - "tls": whevener the channel is encrypted (json-bool) + +Example: + +{ "timestamp": {"seconds": 1290688046, "microseconds": 417172}, + "event": "SPICE_INITIALIZED", + "data": {"server": {"auth": "spice", "port": "5921", + "family": "ipv4", "host": "127.0.0.1"}, + "client": {"port": "49004", "family": "ipv4", "channel-type": 3, + "connection-id": 1804289383, "host": "127.0.0.1", + "channel-id": 0, "tls": true} +}} + +STOP +---- + +Emitted when the Virtual Machine is stopped. + +Data: None. + +Example: + +{ "event": "STOP", + "timestamp": { "seconds": 1267041730, "microseconds": 281295 } } + +SUSPEND +------- + +Emitted when guest enters S3 state. + +Data: None. + +Example: + +{ "event": "SUSPEND", + "timestamp": { "seconds": 1344456160, "microseconds": 309119 } } + +SUSPEND_DISK +------------ + +Emitted when the guest makes a request to enter S4 state. + +Data: None. + +Example: + +{ "event": "SUSPEND_DISK", + "timestamp": { "seconds": 1344456160, "microseconds": 309119 } } + +Note: QEMU shuts down when entering S4 state. + +VNC_CONNECTED +------------- + +Emitted when a VNC client establishes a connection. + +Data: + +- "server": Server information (json-object) + - "host": IP address (json-string) + - "service": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + - "auth": authentication method (json-string, optional) +- "client": Client information (json-object) + - "host": IP address (json-string) + - "service": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + +Example: + +{ "event": "VNC_CONNECTED", + "data": { + "server": { "auth": "sasl", "family": "ipv4", + "service": "5901", "host": "0.0.0.0" }, + "client": { "family": "ipv4", "service": "58425", + "host": "127.0.0.1" } }, + "timestamp": { "seconds": 1262976601, "microseconds": 975795 } } + + +Note: This event is emitted before any authentication takes place, thus +the authentication ID is not provided. + +VNC_DISCONNECTED +---------------- + +Emitted when the connection is closed. + +Data: + +- "server": Server information (json-object) + - "host": IP address (json-string) + - "service": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + - "auth": authentication method (json-string, optional) +- "client": Client information (json-object) + - "host": IP address (json-string) + - "service": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + - "x509_dname": TLS dname (json-string, optional) + - "sasl_username": SASL username (json-string, optional) + +Example: + +{ "event": "VNC_DISCONNECTED", + "data": { + "server": { "auth": "sasl", "family": "ipv4", + "service": "5901", "host": "0.0.0.0" }, + "client": { "family": "ipv4", "service": "58425", + "host": "127.0.0.1", "sasl_username": "luiz" } }, + "timestamp": { "seconds": 1262976601, "microseconds": 975795 } } + +VNC_INITIALIZED +--------------- + +Emitted after authentication takes place (if any) and the VNC session is +made active. + +Data: + +- "server": Server information (json-object) + - "host": IP address (json-string) + - "service": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + - "auth": authentication method (json-string, optional) +- "client": Client information (json-object) + - "host": IP address (json-string) + - "service": port number (json-string) + - "family": address family (json-string, "ipv4" or "ipv6") + - "x509_dname": TLS dname (json-string, optional) + - "sasl_username": SASL username (json-string, optional) + +Example: + +{ "event": "VNC_INITIALIZED", + "data": { + "server": { "auth": "sasl", "family": "ipv4", + "service": "5901", "host": "0.0.0.0"}, + "client": { "family": "ipv4", "service": "46089", + "host": "127.0.0.1", "sasl_username": "luiz" } }, + "timestamp": { "seconds": 1263475302, "microseconds": 150772 } } + +WAKEUP +------ + +Emitted when the guest has woken up from S3 and is running. + +Data: None. + +Example: + +{ "event": "WATCHDOG", + "timestamp": { "seconds": 1344522075, "microseconds": 745528 } } + +WATCHDOG +-------- + +Emitted when the watchdog device's timer is expired. + +Data: + +- "action": Action that has been taken, it's one of the following (json-string): + "reset", "shutdown", "poweroff", "pause", "debug", or "none" + +Example: + +{ "event": "WATCHDOG", + "data": { "action": "reset" }, + "timestamp": { "seconds": 1267061043, "microseconds": 959568 } } + +Note: If action is "reset", "shutdown", or "pause" the WATCHDOG event is +followed respectively by the RESET, SHUTDOWN, or STOP events. + +GUEST_PANICKED +-------------- + +Emitted when guest OS panic is detected. + +Data: + +- "action": Action that has been taken (json-string, currently always "pause"). + +Example: + +{ "event": "GUEST_PANICKED", + "data": { "action": "pause" } } diff --git a/docs/qmp/qmp-spec.txt b/docs/qmp/qmp-spec.txt new file mode 100644 index 0000000000..a27789692b --- /dev/null +++ b/docs/qmp/qmp-spec.txt @@ -0,0 +1,282 @@ + QEMU Monitor Protocol Specification - Version 0.1 + +1. Introduction +=============== + +This document specifies the QEMU Monitor Protocol (QMP), a JSON-based protocol +which is available for applications to control QEMU at the machine-level. + +To enable QMP support, QEMU has to be run in "control mode". This is done by +starting QEMU with the appropriate command-line options. Please, refer to the +QEMU manual page for more information. + +2. Protocol Specification +========================= + +This section details the protocol format. For the purpose of this document +"Client" is any application which is communicating with QEMU in control mode, +and "Server" is QEMU itself. + +JSON data structures, when mentioned in this document, are always in the +following format: + + json-DATA-STRUCTURE-NAME + +Where DATA-STRUCTURE-NAME is any valid JSON data structure, as defined by +the JSON standard: + +http://www.ietf.org/rfc/rfc4627.txt + +For convenience, json-object members and json-array elements mentioned in +this document will be in a certain order. However, in real protocol usage +they can be in ANY order, thus no particular order should be assumed. + +2.1 General Definitions +----------------------- + +2.1.1 All interactions transmitted by the Server are json-objects, always + terminating with CRLF + +2.1.2 All json-objects members are mandatory when not specified otherwise + +2.2 Server Greeting +------------------- + +Right when connected the Server will issue a greeting message, which signals +that the connection has been successfully established and that the Server is +ready for capabilities negotiation (for more information refer to section +'4. Capabilities Negotiation'). + +The format is: + +{ "QMP": { "version": json-object, "capabilities": json-array } } + + Where, + +- The "version" member contains the Server's version information (the format + is the same of the 'query-version' command) +- The "capabilities" member specify the availability of features beyond the + baseline specification + +2.3 Issuing Commands +-------------------- + +The format for command execution is: + +{ "execute": json-string, "arguments": json-object, "id": json-value } + + Where, + +- The "execute" member identifies the command to be executed by the Server +- The "arguments" member is used to pass any arguments required for the + execution of the command, it is optional when no arguments are required +- The "id" member is a transaction identification associated with the + command execution, it is optional and will be part of the response if + provided + +2.4 Commands Responses +---------------------- + +There are two possible responses which the Server will issue as the result +of a command execution: success or error. + +2.4.1 success +------------- + +The success response is issued when the command execution has finished +without errors. + +The format is: + +{ "return": json-object, "id": json-value } + + Where, + +- The "return" member contains the command returned data, which is defined + in a per-command basis or an empty json-object if the command does not + return data +- The "id" member contains the transaction identification associated + with the command execution (if issued by the Client) + +2.4.2 error +----------- + +The error response is issued when the command execution could not be +completed because of an error condition. + +The format is: + +{ "error": { "class": json-string, "desc": json-string }, "id": json-value } + + Where, + +- The "class" member contains the error class name (eg. "GenericError") +- The "desc" member is a human-readable error message. Clients should + not attempt to parse this message. +- The "id" member contains the transaction identification associated with + the command execution (if issued by the Client) + +NOTE: Some errors can occur before the Server is able to read the "id" member, +in these cases the "id" member will not be part of the error response, even +if provided by the client. + +2.5 Asynchronous events +----------------------- + +As a result of state changes, the Server may send messages unilaterally +to the Client at any time. They are called 'asynchronous events'. + +The format is: + +{ "event": json-string, "data": json-object, + "timestamp": { "seconds": json-number, "microseconds": json-number } } + + Where, + +- The "event" member contains the event's name +- The "data" member contains event specific data, which is defined in a + per-event basis, it is optional +- The "timestamp" member contains the exact time of when the event occurred + in the Server. It is a fixed json-object with time in seconds and + microseconds + +For a listing of supported asynchronous events, please, refer to the +qmp-events.txt file. + +3. QMP Examples +=============== + +This section provides some examples of real QMP usage, in all of them +'C' stands for 'Client' and 'S' stands for 'Server'. + +3.1 Server greeting +------------------- + +S: {"QMP": {"version": {"qemu": "0.12.50", "package": ""}, "capabilities": []}} + +3.2 Simple 'stop' execution +--------------------------- + +C: { "execute": "stop" } +S: {"return": {}} + +3.3 KVM information +------------------- + +C: { "execute": "query-kvm", "id": "example" } +S: {"return": {"enabled": true, "present": true}, "id": "example"} + +3.4 Parsing error +------------------ + +C: { "execute": } +S: {"error": {"class": "GenericError", "desc": "Invalid JSON syntax" } } + +3.5 Powerdown event +------------------- + +S: {"timestamp": {"seconds": 1258551470, "microseconds": 802384}, "event": +"POWERDOWN"} + +4. Capabilities Negotiation +---------------------------- + +When a Client successfully establishes a connection, the Server is in +Capabilities Negotiation mode. + +In this mode only the 'qmp_capabilities' command is allowed to run, all +other commands will return the CommandNotFound error. Asynchronous messages +are not delivered either. + +Clients should use the 'qmp_capabilities' command to enable capabilities +advertised in the Server's greeting (section '2.2 Server Greeting') they +support. + +When the 'qmp_capabilities' command is issued, and if it does not return an +error, the Server enters in Command mode where capabilities changes take +effect, all commands (except 'qmp_capabilities') are allowed and asynchronous +messages are delivered. + +5 Compatibility Considerations +------------------------------ + +All protocol changes or new features which modify the protocol format in an +incompatible way are disabled by default and will be advertised by the +capabilities array (section '2.2 Server Greeting'). Thus, Clients can check +that array and enable the capabilities they support. + +The QMP Server performs a type check on the arguments to a command. It +generates an error if a value does not have the expected type for its +key, or if it does not understand a key that the Client included. The +strictness of the Server catches wrong assumptions of Clients about +the Server's schema. Clients can assume that, when such validation +errors occur, they will be reported before the command generated any +side effect. + +However, Clients must not assume any particular: + +- Length of json-arrays +- Size of json-objects; in particular, future versions of QEMU may add + new keys and Clients should be able to ignore them. +- Order of json-object members or json-array elements +- Amount of errors generated by a command, that is, new errors can be added + to any existing command in newer versions of the Server + +Of course, the Server does guarantee to send valid JSON. But apart from +this, a Client should be "conservative in what they send, and liberal in +what they accept". + +6. Downstream extension of QMP +------------------------------ + +We recommend that downstream consumers of QEMU do *not* modify QMP. +Management tools should be able to support both upstream and downstream +versions of QMP without special logic, and downstream extensions are +inherently at odds with that. + +However, we recognize that it is sometimes impossible for downstreams to +avoid modifying QMP. Both upstream and downstream need to take care to +preserve long-term compatibility and interoperability. + +To help with that, QMP reserves JSON object member names beginning with +'__' (double underscore) for downstream use ("downstream names"). This +means upstream will never use any downstream names for its commands, +arguments, errors, asynchronous events, and so forth. + +Any new names downstream wishes to add must begin with '__'. To +ensure compatibility with other downstreams, it is strongly +recommended that you prefix your downstram names with '__RFQDN_' where +RFQDN is a valid, reverse fully qualified domain name which you +control. For example, a qemu-kvm specific monitor command would be: + + (qemu) __org.linux-kvm_enable_irqchip + +Downstream must not change the server greeting (section 2.2) other than +to offer additional capabilities. But see below for why even that is +discouraged. + +Section '5 Compatibility Considerations' applies to downstream as well +as to upstream, obviously. It follows that downstream must behave +exactly like upstream for any input not containing members with +downstream names ("downstream members"), except it may add members +with downstream names to its output. + +Thus, a client should not be able to distinguish downstream from +upstream as long as it doesn't send input with downstream members, and +properly ignores any downstream members in the output it receives. + +Advice on downstream modifications: + +1. Introducing new commands is okay. If you want to extend an existing + command, consider introducing a new one with the new behaviour + instead. + +2. Introducing new asynchronous messages is okay. If you want to extend + an existing message, consider adding a new one instead. + +3. Introducing new errors for use in new commands is okay. Adding new + errors to existing commands counts as extension, so 1. applies. + +4. New capabilities are strongly discouraged. Capabilities are for + evolving the basic protocol, and multiple diverging basic protocol + dialects are most undesirable. |