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NAME | DESCRIPTION | AUTHOR | COPYRIGHT | COLOPHON |
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OVSDB-SERVER(7) Open vSwitch OVSDB-SERVER(7)
ovsdb-server - Open vSwitch Database Server Protocol
ovsdb-server implements the Open vSwitch Database (OVSDB)
protocol specified in RFC 7047. This document provides
clarifications for how ovsdb-server implements the protocol and
describes the extensions that it provides beyond RFC 7047.
Numbers in section headings refer to corresponding sections in
RFC 7047.
3.1 JSON Usage
RFC 4627 says that names within a JSON object should be unique.
The Open vSwitch JSON parser discards all but the last value for
a name that is specified more than once.
The definition of <error> allows for implementation extensions.
Currently ovsdb-server uses the following additional error
strings (which might change in later releases):
syntax error or unknown column
The request could not be parsed as an OVSDB request. An
additional syntax member, whose value is a string that
contains JSON, may narrow down the particular syntax that
could not be parsed.
internal error
The request triggered a bug in ovsdb-server.
ovsdb error
A map or set contains a duplicate key.
permission error
The request was denied by the role-based access control
extension, introduced in version 2.8.
3.2 Schema Format
RFC 7047 requires the version field in <database-schema>.
Current versions of ovsdb-server allow it to be omitted (future
versions are likely to require it).
RFC 7047 allows columns that contain weak references to be
immutable. This raises the issue of the behavior of the weak
reference when the rows that it references are deleted. Since
version 2.6, ovsdb-server forces columns that contain weak
references to be mutable.
Since version 2.8, the table name RBAC_Role is used internally by
the role-based access control extension to ovsdb-server and
should not be used for purposes other than defining mappings of
role names to table access permissions. This table has one row
per role name and the following columns:
name The role name.
permissions
A map of table name to a reference to a row in a separate
permission table.
The separate RBAC permission table has one row per access control
configuration and the following columns:
name The name of the table to which the row applies.
authorization
The set of column names and column:key pairs to be
compared with the client ID in order to determine the
authorization status of the requested operation.
insert_delete
A boolean value, true if authorized insertions and
deletions are allowed, false if no insertions or deletions
are allowed.
update The set of columns and column:key pairs for which
authorized update and mutate operations should be
permitted.
4 Wire Protocol
The original OVSDB specifications included the following reasons,
omitted from RFC 7047, to operate JSON-RPC directly over a stream
instead of over HTTP:
• JSON-RPC is a peer-to-peer protocol, but HTTP is a
client-server protocol, which is a poor match. Thus, JSON-RPC
over HTTP requires the client to periodically poll the server
to receive server requests.
• HTTP is more complicated than stream connections and doesn’t
provide any corresponding advantage.
• The JSON-RPC specification for HTTP transport is incomplete.
4.1.3 Transact
Since version 2.8, role-based access controls can be applied to
operations within a transaction that would modify the contents of
the database (these operations include row insert, row delete,
column update, and column mutate). Role-based access controls are
applied when the database schema contains a table with the name
RBAC_Role and the connection on which the transaction request was
received has an associated role name (from the role column in the
remote connection table). When role-based access controls are
enabled, transactions that are otherwise well-formed may be
rejected depending on the client’s role, ID, and the contents of
the RBAC_Role table and associated permissions table.
4.1.5 Monitor
For backward compatibility, ovsdb-server currently permits a
single <monitor-request> to be used instead of an array; it is
treated as a single-element array. Future versions of
ovsdb-server might remove this compatibility feature.
Because the <json-value> parameter is used to match subsequent
update notifications (see below) to the request, it must be
unique among all active monitors. ovsdb-server rejects attempt
to create two monitors with the same identifier.
When a given client sends a transact request that changes a table
that the same client is monitoring, ovsdb-server always sends the
update (or update2 or update3) for these changes before it sends
the reply to the transact request. Thus, when a client receives
a transact reply, it can know immediately what changes (if any)
the transaction made. (If ovsdb-server might use the other
order, then a client that wishes to act on based on the results
of its own transactions would not know when this was guaranteed
to have taken place.)
4.1.7 Monitor Cancellation
When a database monitored by a session is removed, and database
change awareness is enabled for the session (see Section 4.1.16),
the database server spontaneously cancels all monitors (including
conditional monitors described in Section 4.1.12) for the removed
database. For each canceled monitor, it issues a notification in
the following form:
"method": "monitor_canceled"
"params": [<json-value>]
"id": null
4.1.12 Monitor_cond
A new monitor method added in Open vSwitch version 2.6. The
monitor_cond request enables a client to replicate subsets of
tables within an OVSDB database by requesting notifications of
changes to rows matching one of the conditions specified in where
by receiving the specified contents of these rows when table
updates occur. monitor_cond also allows a more efficient update
notifications by receiving <table-updates2> notifications
(described below).
The monitor method described in Section 4.1.5 also applies to
monitor_cond, with the following exceptions:
• RPC request method becomes monitor_cond.
• Reply result follows <table-updates2>, described in Section
4.1.14.
• Subsequent changes are sent to the client using the update2
monitor notification, described in Section 4.1.14
• Update notifications are being sent only for rows matching
[<condition>*].
The request object has the following members:
"method": "monitor_cond"
"params": [<db-name>, <json-value>, <monitor-cond-requests>]
"id": <nonnull-json-value>
The <json-value> parameter is used to match subsequent update
notifications (see below) to this request. The
<monitor-cond-requests> object maps the name of the table to an
array of <monitor-cond-request>.
Each <monitor-cond-request> is an object with the following
members:
"columns": [<column>*] optional
"where": [<condition>*] optional
"select": <monitor-select> optional
The columns, if present, define the columns within the table to
be monitored that match conditions. If not present, all columns
are monitored.
The where, if present, is a JSON array of <condition> and boolean
values. If not present or condition is an empty array, implicit
True will be considered and updates on all rows will be sent.
<monitor-select> is an object with the following members:
"initial": <boolean> optional
"insert": <boolean> optional
"delete": <boolean> optional
"modify": <boolean> optional
The contents of this object specify how the columns or table are
to be monitored as explained in more detail below.
The response object has the following members:
"result": <table-updates2>
"error": null
"id": same "id" as request
The <table-updates2> object is described in detail in Section
4.1.14. It contains the contents of the tables for which initial
rows are selected. If no tables initial contents are requested,
then result is an empty object.
Subsequently, when changes to a specified table that match one of
the conditions in <monitor-cond-request> are committed, the
changes are automatically sent to the client using the update2
monitor notification (see Section 4.1.14). This monitoring
persists until the JSON-RPC session terminates or until the
client sends a monitor_cancel JSON-RPC request.
Each <monitor-cond-request> specifies one or more conditions and
the manner in which the rows that match the conditions are to be
monitored. The circumstances in which an update notification is
sent for a row within the table are determined by
<monitor-select>:
• If initial is omitted or true, every row in the original table
that matches one of the conditions is sent as part of the
response to the monitor_cond request.
• If insert is omitted or true, update notifications are sent for
rows newly inserted into the table that match conditions or for
rows modified in the table so that their old version does not
match the condition and new version does.
• If delete is omitted or true, update notifications are sent for
rows deleted from the table that match conditions or for rows
modified in the table so that their old version does match the
conditions and new version does not.
• If modify is omitted or true, update notifications are sent
whenever a row in the table that matches conditions in both old
and new version is modified.
Both monitor and monitor_cond sessions can exist concurrently.
However, monitor and monitor_cond shares the same <json-value>
parameter space; it must be unique among all monitor and
monitor_cond sessions.
4.1.13 Monitor_cond_change
The monitor_cond_change request enables a client to change an
existing monitor_cond replication of the database by specifying a
new condition and columns for each replicated table. Currently
changing the columns set is not supported.
The request object has the following members:
"method": "monitor_cond_change"
"params": [<json-value>, <json-value>, <monitor-cond-update-requests>]
"id": <nonnull-json-value>
The <json-value> parameter should have a value of an existing
conditional monitoring session from this client. The second
<json-value> in params array is the requested value for this
session. This value is valid only after monitor_cond_change is
committed. A user can use these values to distinguish between
update messages before conditions update and after. The
<monitor-cond-update-requests> object maps the name of the table
to an array of <monitor-cond-update-request>. Monitored tables
not included in <monitor-cond-update-requests> retain their
current conditions.
Each <monitor-cond-update-request> is an object with the
following members:
"columns": [<column>*] optional
"where": [<condition>*] optional
The columns specify a new array of columns to be monitored,
although this feature is not yet supported.
The where specify a new array of conditions to be applied to this
monitoring session.
The response object has the following members:
"result": {}
"error": null
"id": same "id" as request
Subsequent <table-updates2> notifications are described in detail
in Section 4.1.14 in the RFC. If insert contents are requested
by original monitor_cond request, <table-updates2> will contain
rows that match the new condition and do not match the old
condition. If deleted contents are requested by origin monitor
request, <table-updates2> will contain any matched rows by old
condition and not matched by the new condition.
Changes according to the new conditions are automatically sent to
the client using the update2 or update3 monitor notification
depending on the monitor method. An update, if any, as a result
of a condition change, will be sent to the client before the
reply to the monitor_cond_change request.
4.1.14 Update2 notification
The update2 notification is sent by the server to the client to
report changes in tables that are being monitored following a
monitor_cond request as described above. The notification has the
following members:
"method": "update2"
"params": [<json-value>, <table-updates2>]
"id": null
The <json-value> in params is the same as the value passed as the
<json-value> in params for the corresponding monitor request.
<table-updates2> is an object that maps from a table name to a
<table-update2>. A <table-update2> is an object that maps from
row’s UUID to a <row-update2> object. A <row-update2> is an
object with one of the following members:
"initial": <row>
present for initial updates
"insert": <row>
present for insert updates
"delete": <row>
present for delete updates
"modify": <row>"
present for modify updates
The format of <row> is described in Section 5.1.
<row> is always a null object for a delete update. In initial
and insert updates, <row> omits columns whose values equal the
default value of the column type.
For a modify update, <row> contains only the columns that are
modified. <row> stores the difference between the old and new
value for those columns, as described below.
For columns with single value, the difference is the value of the
new column.
The difference between two sets are all elements that only belong
to one of the sets.
The difference between two maps are all key-value pairs whose
keys appears in only one of the maps, plus the key-value pairs
whose keys appear in both maps but with different values. For
the latter elements, <row> includes the value from the new
column.
Initial views of rows are not presented in update2 notifications,
but in the response object to the monitor_cond request. The
formatting of the <table-updates2> object, however, is the same
in either case.
4.1.15 Monitor_cond_since
A new monitor method added in Open vSwitch version 2.12. The
monitor_cond_since request enables a client to request changes
that happened after a specific transaction id. A client can use
this feature to request only latest changes after a server
connection reset instead of re-transfer all data from the server
again.
The monitor_cond method described in Section 4.1.12 also applies
to monitor_cond_since, with the following exceptions:
• RPC request method becomes monitor_cond_since.
• Reply result includes extra parameters.
• Subsequent changes are sent to the client using the update3
monitor notification, described in Section 4.1.16
The request object has the following members:
"method": "monitor_cond_since"
"params": [<db-name>, <json-value>, <monitor-cond-requests>, <last-txn-id>]
"id": <nonnull-json-value>
The <last-txn-id> parameter is the transaction id that identifies
the latest data the client already has, and it requests server to
send changes AFTER this transaction (exclusive).
All other parameters are the same as monitor_cond method.
The response object has the following members:
"result": [<found>, <last-txn-id>, <table-updates2>]
"error": null
"id": same "id" as request
The <found> is a boolean value that tells if the <last-txn-id>
requested by client is found in server’s history or not. If true,
the changes after that version up to current is sent. Otherwise,
all data is sent.
The <last-txn-id> is the transaction id that identifies the
latest transaction included in the changes in <table-updates2> of
this response, so that client can keep tracking. If there is no
change involved in this response, it is the same as the
<last-txn-id> in the request if <found> is true, or zero uuid if
<found> is false. If the server does not support transaction
uuid, it will be zero uuid as well.
All other parameters are the same as in response object of
monitor_cond method.
Like in monitor_cond, subsequent changes that match conditions in
<monitor-cond-request> are automatically sent to the client, but
using update3 monitor notification (see Section 4.1.16), instead
of update2.
4.1.16 Update3 notification
The update3 notification is sent by the server to the client to
report changes in tables that are being monitored following a
monitor_cond_since request as described above. The notification
has the following members:
"method": "update3"
"params": [<json-value>, <last-txn-id>, <table-updates2>]
"id": null
The <last-txn-id> is the same as described in the response object
of monitor_cond_since.
All other parameters are the same as in update2 monitor
notification (see Section 4.1.14).
4.1.17 Get Server ID
A new RPC method added in Open vSwitch version 2.7. The request
contains the following members:
"method": "get_server_id"
"params": null
"id": <nonnull-json-value>
The response object contains the following members:
"result": "<server_id>"
"error": null
"id": same "id" as request
<server_id> is JSON string that contains a UUID that uniquely
identifies the running OVSDB server process. A fresh UUID is
generated when the process restarts.
4.1.18 Database Change Awareness
RFC 7047 does not provide a way for a client to find out about
some kinds of configuration changes, such as about databases
added or removed while a client is connected to the server, or
databases changing between read/write and read-only due to a
transition between active and backup roles. Traditionally,
ovsdb-server disconnects all of its clients when this happens,
because this prompts a well-written client to reassess what is
available from the server when it reconnects.
OVS 2.9 provides a way for clients to keep track of these kinds
of changes, by monitoring the Database table in the _Server
database introduced in this release (see ovsdb-server(5) for
details). By itself, this does not suppress ovsdb-server
disconnection behavior, because a client might monitor this
database without understanding its special semantics. Instead,
ovsdb-server provides a special request:
"method": "set_db_change_aware"
"params": [<boolean>]
"id": <nonnull-json-value>
If the boolean in the request is true, it suppresses the
connection-closing behavior for the current connection, and false
restores the default behavior. The reply is always the same:
"result": {}
"error": null
"id": same "id" as request
4.1.19 Schema Conversion
Open vSwitch 2.9 adds a new JSON-RPC request to convert an online
database from one schema to another. The request contains the
following members:
"method": "convert"
"params": [<db-name>, <database-schema>]
"id": <nonnull-json-value>
Upon receipt, the server converts database <db-name> to schema
<database-schema>. The schema’s name must be <db-name>. The
conversion is atomic, consistent, isolated, and durable. The
data in the database must be valid when interpreted under
<database-schema>, with only one exception: data for tables and
columns that do not exist in the new schema are ignored. Columns
that exist in <database-schema> but not in the database are set
to their default values. All of the new schema’s constraints
apply in full.
If the conversion is successful, the server notifies clients that
use the set_db_change_aware RPC introduced in Open vSwitch 2.9
and cancels their outstanding transactions and monitors. The
server disconnects other clients, enabling them to notice the
change when they reconnect. The server sends the following
reply:
"result": {}
"error": null
"id": same "id" as request
If the conversion fails, then the server sends an error reply in
the following form:
"result": null
"error": [<error>]
"id": same "id" as request
5.1 Notation
For <condition>, RFC 7047 only allows the use of !=, ==,
includes, and excludes operators with set types. Open vSwitch
2.4 and later extend <condition> to allow the use of <, <=, >=,
and > operators with a column with type “set of 0 or 1 integer”
and an integer argument, and with “set of 0 or 1 real” and a real
argument. These conditions evaluate to false when the column is
empty, and otherwise as described in RFC 7047 for integer and
real types.
<condition> is specified in Section 5.1 in the RFC with the
following change: A condition can be either a 3-element JSON
array as described in the RFC or a boolean value. In case of an
empty array an implicit true boolean value will be considered.
5.2.1 Insert
As an extension, Open vSwitch 2.13 and later allow an optional
uuid member to specify the UUID for the new row. The specified
UUID must be unique within the table when it is inserted and not
the UUID of a row previously deleted within the transaction. If
the UUID violates these rules, then the operation fails with a
duplicate uuid error.
5.2.6 Wait, 5.2.7 Commit, 5.2.9 Comment
RFC 7047 says that the wait, commit, and comment operations have
no corresponding result object. This is not true. Instead, when
such an operation is successful, it yields a result object with
no members.
The Open vSwitch Development Community
2016-2021, The Open vSwitch Development Community
This page is part of the Open vSwitch (a distributed virtual
multilayer switch) project. Information about the project can be
found at ⟨http://openvswitch.org/⟩. If you have a bug report for
this manual page, send it to bugs@openvswitch.org. This page was
obtained from the project's upstream Git repository
⟨https://github.com/openvswitch/ovs.git⟩ on 2023-12-22. (At that
time, the date of the most recent commit that was found in the
repository was 2023-12-21.) If you discover any rendering
problems in this HTML version of the page, or you believe there
is a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
3.2.90 Dec 22, 2023 OVSDB-SERVER(7)
Pages that refer to this page: ovsdb-server(1), ovsdb-server(5)
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HTML rendering created 2023-12-22 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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