diff options
author | Luiz Capitulino <lcapitulino@redhat.com> | 2013-09-10 17:00:45 -0400 |
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committer | Luiz Capitulino <lcapitulino@redhat.com> | 2013-09-18 08:57:02 -0400 |
commit | 7537fe0487c3f7991584ca1c4bf9b6c58cd33968 (patch) | |
tree | 118664e8db755f95683b4e141724e802a2c818b0 /QMP | |
parent | d076a2adddece29ad33afcce01e441bfc1c6923d (diff) |
QMP: QMP/ -> docs/qmp/
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Diffstat (limited to 'QMP')
-rw-r--r-- | QMP/README | 88 | ||||
-rw-r--r-- | QMP/qmp-events.txt | 502 | ||||
-rw-r--r-- | QMP/qmp-spec.txt | 282 |
3 files changed, 0 insertions, 872 deletions
diff --git a/QMP/README b/QMP/README deleted file mode 100644 index c95a08c234..0000000000 --- a/QMP/README +++ /dev/null @@ -1,88 +0,0 @@ - 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/QMP/qmp-events.txt b/QMP/qmp-events.txt deleted file mode 100644 index 4b24ec900d..0000000000 --- a/QMP/qmp-events.txt +++ /dev/null @@ -1,502 +0,0 @@ - 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/QMP/qmp-spec.txt b/QMP/qmp-spec.txt deleted file mode 100644 index a27789692b..0000000000 --- a/QMP/qmp-spec.txt +++ /dev/null @@ -1,282 +0,0 @@ - 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. |