.\" $OpenBSD: agentx.3,v 1.10 2022/10/14 21:44:06 jmc Exp $
.\"
.\" Copyright (c) 2020 Martijn van Duren <martijn@openbsd.org>
.\"
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.\" purpose with or without fee is hereby granted, provided that the above
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.Dd $Mdocdate: October 14 2022 $
.Dt AGENTX 3
.Os
.Sh NAME
.Nm agentx_log_fatal ,
.Nm agentx_log_warn ,
.Nm agentx_log_info ,
.Nm agentx_log_debug ,
.Nm agentx ,
.Nm agentx_connect ,
.Nm agentx_retry ,
.Nm agentx_read ,
.Nm agentx_write ,
.Nm agentx_wantwrite ,
.Nm agentx_free ,
.Nm agentx_session ,
.Nm agentx_session_free ,
.Nm agentx_context ,
.Nm agentx_context_object_find ,
.Nm agentx_context_object_nfind ,
.Nm agentx_context_uptime ,
.Nm agentx_context_free ,
.Nm agentx_region ,
.Nm agentx_region_free ,
.Nm agentx_agentcaps ,
.Nm agentx_agentcaps_free ,
.Nm agentx_index_integer_new ,
.Nm agentx_index_integer_any ,
.Nm agentx_index_integer_value ,
.Nm agentx_index_integer_dynamic ,
.Nm agentx_index_string_dynamic ,
.Nm agentx_index_nstring_dynamic ,
.Nm agentx_index_oid_dynamic ,
.Nm agentx_index_noid_dynamic ,
.Nm agentx_index_ipaddress_dynamic ,
.Nm agentx_index_free ,
.Nm agentx_object ,
.Nm agentx_object_free ,
.Nm agentx_varbind_integer ,
.Nm agentx_varbind_string ,
.Nm agentx_varbind_nstring ,
.Nm agentx_varbind_printf ,
.Nm agentx_varbind_null ,
.Nm agentx_varbind_oid ,
.Nm agentx_varbind_object ,
.Nm agentx_varbind_index ,
.Nm agentx_varbind_ipaddress ,
.Nm agentx_varbind_counter32 ,
.Nm agentx_varbind_gauge32 ,
.Nm agentx_varbind_unsigned32 ,
.Nm agentx_varbind_timeticks ,
.Nm agentx_varbind_opaque ,
.Nm agentx_varbind_counter64 ,
.Nm agentx_varbind_notfound ,
.Nm agentx_varbind_error ,
.Nm agentx_varbind_request ,
.Nm agentx_varbind_get_index_integer ,
.Nm agentx_varbind_get_index_string ,
.Nm agentx_varbind_get_index_oid ,
.Nm agentx_varbind_get_index_ipaddress ,
.Nm agentx_varbind_set_index_integer ,
.Nm agentx_varbind_set_index_string ,
.Nm agentx_varbind_set_index_nstring ,
.Nm agentx_varbind_set_index_oid ,
.Nm agentx_varbind_set_index_object ,
.Nm agentx_varbind_set_index_ipaddress
.Nd manage an interface to an agentx master
.Sh SYNOPSIS
.In agentx.h
.Ft extern void
.Fn (*agentx_log_fatal) "const char *fmt" ...
.Ft extern void
.Fn (*agentx_log_warn) "const char *fmt" ...
.Ft extern void
.Fn (*agentx_log_info) "const char *fmt" ...
.Ft extern void
.Fn (*agentx_log_debug) "const char *fmt" ...
.Ft struct agentx *
.Fn agentx "void (*nofd)(struct agentx *, void *, int)" "void *cookie"
.Ft void
.Fn agentx_connect "struct agentx *sa" "int fd"
.Ft void
.Fn agentx_retry "struct agentx *sa"
.Ft void
.Fn agentx_read "struct agentx *sa"
.Ft void
.Fn agentx_write "struct agentx *sa"
.Ft extern void
.Fn (*agentx_wantwrite) "struct agentx *sa" "int fd"
.Ft void
.Fn agentx_free "struct agentx *sa"
.Ft struct agentx_session *
.Fo agentx_session
.Fa "struct agentx *sa" "uint32_t oid[]" "size_t oidlen"
.Fa "const char *descr" "uint8_t timeout"
.Fc
.Ft void
.Fn agentx_session_free "struct agentx_session *sas"
.Ft struct agentx_context *
.Fn agentx_context "struct agentx_session *sas" "const char *name"
.Ft struct agentx_object *
.Fo agentx_context_object_find
.Fa "struct agentx_context *sac" "const uint32_t oid[]" "size_t oidlen"
.Fa "int active" "int instance"
.Fc
.Ft struct agentx_object *
.Fo agentx_context_object_nfind
.Fa "struct agentx_context *" "const uint32_t oid[]" "size_t oidlen"
.Fa "int active" "int inclusive"
.Fc
.Ft uint32_t
.Fn agentx_context_uptime "struct agentx_context *sac"
.Ft void
.Fn agentx_context_free "struct agentx_context *sac"
.Ft struct agentx_agentcaps *
.Fo agentx_agentcaps
.Fa "struct agentx_context *sac" "uint32_t oid[]" "size_t oidlen"
.Fa "const char *descr"
.Fc
.Ft void
.Fn agentx_agentcaps_free "struct agentx_agentcaps *saa"
.Ft struct agentx_region *
.Fo agentx_region
.Fa "struct agentx_context *sac" "uint32_t oid[]"
.Fa "size_t oidlen" "uint8_t timeout"
.Fc
.Ft void
.Fn agentx_region_free "struct agentx_region *sar"
.Ft struct agentx_index *
.Fo agentx_index_integer_new
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fc
.Ft struct agentx_index *
.Fo agentx_index_integer_any
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fc
.Ft struct agentx_index *
.Fo agentx_index_integer_value
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fa "int32_t value"
.Fc
.Ft struct agentx_index *
.Fo agentx_index_integer_dynamic
.Fa "struct agentx_region *sar" "uint32_t oid[] "size_t oidlen"
.Fc
.Ft struct agentx_index *
.Fo agentx_index_string_dynamic
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fc
.Ft struct agentx_index *
.Fo agentx_index_nstring_dynamic
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fa "size_t slen"
.Fc
.Ft struct agentx_index *
.Fo agentx_index_oid_dynamic
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fc
.Ft struct agentx_index *
.Fo agentx_index_noid_dynamic
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fa "size_t vlen"
.Fc
.Ft struct agentx_index *
.Fo agentx_index_ipaddress_dynamic
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fc
.Ft void
.Fn agentx_index_free "struct agentx_index *sai"
.Ft struct agentx_object *
.Fo agentx_object
.Fa "struct agentx_region *sar" "uint32_t oid[]" "size_t oidlen"
.Fa "struct agentx_index *index[]" "size_t indexlen" "int implied"
.Fa "void (*getcb)(struct agentx_varbind *)"
.Fc
.Ft void
.Fn agentx_object_free "struct agentx_object *sao"
.Ft void
.Fn agentx_varbind_integer "struct agentx_varbind *sav" "int32_t value"
.Ft void
.Fn agentx_varbind_string "struct agentx_varbind *sav" "const char *value"
.Ft void
.Fo agentx_varbind_nstring
.Fa "struct agentx_varbind *sav" "const char *value" "size_t slen"
.Fc
.Ft void
.Fo agentx_varbind_printf
.Fa "struct agentx_varbind *sav" "const char *fmt" ...
.Fc
.Ft void
.Fn agentx_varbind_null "struct agentx_varbind *sav"
.Ft void
.Fo agentx_varbind_oid
.Fa "struct agentx_varbind *sav" "const uint32_t oid[]" "size_t oidlen"
.Fc
.Ft void
.Fo agentx_varbind_object
.Fa "struct agentx_varbind *sav" "struct agentx_object *sao"
.Fc
.Ft void
.Fo agentx_varbind_index
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fc
.Ft void
.Fo agentx_varbind_ipaddress
.Fa "struct agentx_varbind *sav" "const struct in_addr *addr"
.Fc
.Ft void
.Fn agentx_varbind_counter32 "struct agentx_varbind *sav" "uint32_t value"
.Ft void
.Fn agentx_varbind_gauge32 "struct agentx_varbind *sav" "uint32_t value"
.Ft void
.Fn agentx_varbind_unsigned32 "struct agentx_varbind *sav" "uint32_t value"
.Ft void
.Fo agentx_varbind_timeticks
.Fa "struct agentx_varbind *sav"  "uint32_t value"
.Fc
.Ft void
.Fo agentx_varbind_opaque
.Fa "struct agentx_varbind *sav" "const char *value" "size_t slen"
.Fc
.Ft void
.Fn agentx_varbind_counter64 "struct agentx_varbind *sav" "uint64_t value"
.Ft void
.Fn agentx_varbind_notfound "struct agentx_varbind *sav"
.Ft void
.Fn agentx_varbind_error "struct agentx_varbind *sav"
.Ft enum agentx_request_type
.Fn agentx_varbind_request "struct agentx_varbind *sav"
.Ft int32_t
.Fo agentx_varbind_get_index_integer
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fc
.Ft const unsigned char *
.Fo agentx_varbind_get_index_string
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai" "size_t *slen"
.Fa "int *implied"
.Fc
.Ft const uint32_t *
.Fo agentx_varbind_get_index_oid
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fa "size_t *oidlen" "int *implied"
.Fc
.Ft const struct in_addr *
.Fo agentx_varbind_get_index_ipaddress
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fc
.Ft void
.Fo agentx_varbind_set_index_integer
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fa "int32_t value"
.Fc
.Ft void
.Fo agentx_varbind_set_index_string
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fa "const unsigned char *value"
.Fc
.Ft void
.Fo agentx_varbind_set_index_nstring
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fa "const unsigned char *value" "size_t slen"
.Fc
.Ft void
.Fo agentx_varbind_set_index_oid
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fa "const uint32_t *oid" "size_t oidlen"
.Fc
.Ft void
.Fo agentx_varbind_set_index_object
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fa "struct agentx_object *sao"
.Fc
.Ft void
.Fo agentx_varbind_set_index_ipaddress
.Fa "struct agentx_varbind *sav" "struct agentx_index *sai"
.Fa "const struct in_addr *addr"
.Fc
.Bd -literal
enum agentx_request_type {
        AGENTX_REQUEST_TYPE_GET,
        AGENTX_REQUEST_TYPE_GETNEXT,
        AGENTX_REQUEST_TYPE_GETNEXTINCLUSIVE
};
.Ed
.Fd #define AGENTX_MASTER_PATH \(dq/var/agentx/master\(dq
.Fd #define AGENTX_OID_MAX_LEN 128
.Fd #define AGENTX_OID_INDEX_MAX_LEN 10
.Fd #define AGENTX_OID(...)
.Fd #define AGENTX_MIB2 1, 3, 6, 1, 2, 1
.Fd #define AGENTX_ENTERPRISES 1, 3, 6, 1, 4, 1
.Sh DESCRIPTION
The
.Nm agentx
functions allow an application to describe their MIB layout and provide an
.Fa fd
based interface to control the internal agentx state.
.Nm agentx
is not thread safe.
.Ss DESCRIBING THE MIB
.Nm agentx
is a framework to abstract away the agentx protocol from the application.
For the framework to report information to the administrator, the
.Fn agentx_log_fatal ,
.Fn agentx_log_warn ,
.Fn agentx_log_info
and
.Fn agentx_log_debug
functions must be set.
.Pp
When
.Fa sa
is created by
.Fn agentx
or when
.Fa sa
detects that there is no connection to the agentx master, it calls out to
.Fa nofd
with itself,
.Fa cookie
and an integer
.Fa close
as arguments.
If
.Fa close
is not set,
.Fn nofd
is expected to set up a new
.Fa fd
to the agentx master.
This one can usually be found at
.Dv AGENTX_MASTER_PATH .
This
.Fa fd
can be returned to
.Fa sa
at any moment via
.Fn agentx_connect ,
but must always be done as a result of a call to
.Fn nofd .
Once
.Fn agentx_connect
has been called,
the application is responsible for retrieving data when available
on
.Fa fd
by calling
.Fn agentx_read .
If nonblocking writes are desirable, the
.Fn agentx_wantwrite
pointer can be set to an application function and will be called as soon as
there's data available to be written out.
Once
.Fa fd
is ready for a write, the function
.Fn agentx_write
should be called.
.Pp
If any of the session, agentcaps, region, index, or objects failed to enable
correctly
.Pq as can be seen by the admin through the logs
they can be retried through
.Fn agentx_retry .
.Pp
.Fa sa
can be freed via
.Fn agentx_free .
It will close all active sessions and free all derived objects.
Once freed, no new objects can be derived from the freed objects.
Once all sessions are closed, it will call out to
.Fn nofd
with
.Fa close
set, indicating that the application can clean up any context related to
.Fa sa .
.Pp
On top of the
.Fa sa
connection a
.Vt agentx_session
must be set up.
Normally there's only a single session per
.Fa sa .
The
.Fa timeout
argument specifies the maximum time in seconds the master should wait for a
reply before determining we're gone.
If set to 0, the agentx master determines the timeout.
The
.Fa oid
and
.Fa oidlen
combination identifies the subagent and will be visible through the
agentxSessionObjectID object on the agentx master.
The
.Fa descr
is a short displaystring description of the agent and will be visible through
the agentxSessionDescr object on the agentx master.
.Pp
The
.Vt agentx_context
is the SNMPv3 context in which the objects operate and is built on top of
agentx_session
.Fa sas .
If the default context is requested,
.Fa name
must be NULL.
.Pp
.Fn agentx_agentcaps
registers an entry in the agentx master's sysORTable.
The
.Fa oid ,
.Fa oidlen
combination should point to an AGENT-CAPABILITIES object which describes the
capabilities of the subagent.
.Fa descr
should be a textual description of the capabilities.
If no AGENT-CAPABILITIES object is defined, this function can be omitted.
.Pp
A
.Vt agentx_region
indicates a region inside the object-tree for which get- and set-requests will
be queried.
If the OID has already been claimed by another subagent, it will try to claim it
on a lower priority.
The
.Fa timeout
parameter overrules its
.Vt agentx_session
counterpart.
.Pp
For objects in a table one or more
.Ft agentx_index
elements must be supplied.
.Fn agentx_index_integer_new ,
.Fn agentx_index_integer_any
and
.Fn agentx_index_integer_value
register an integer index at the agentx master.
Of these
.Fn agentx_index_integer_new
registers a new, previously unused, index;
.Fn agentx_index_integer_any
registers the first available index;
and
.Fn agentx_index_integer_value
tries to register a specific value.
If the registration of an index fails, an error will be logged and all objects
using it will remain disabled.
The OID where the index should be registered is documented by the MIB.
These registered indices are usually used for tables where multiple subagents
are registered.
.Pp
For dynamic indices the agentx_index_*_dynamic functions can be used, based
on the data type of the object.
The data type should match the data type in the MIB at the
.Fa oid
object.
Indices of data type string or oid with a fixed length should be created via
.Fn agentx_index_nstring_dynamic
and
.Fn agentx_index_noid_dynamic
respectively.
.Pp
.Vt agentx_object
is an object as described in the MIB.
For scalar objects
.Pq without indices
the final zero must be omitted.
For table entries a list of 1 or more indices must be added via
.Fa index
and
.Fa indexlen .
The list of indices must match the INDEX list on the ENTRY object in the MIB.
The total length of the OID, including indices, can't be more than
.Dv AGENTX_OID_MAX_LEN
and indexlen can't be more than
.Dv AGENTX_OID_INDEX_MAX_LEN .
If
.Fa implied
is set, the final index must be of type OID or string and will omit the leading
length indicator.
This value must only be set if specified in the MIB.
.Fn getcb
will be called for each varbind in a GET, GETNEXT or GETBULK request that
matches the object.
.Ss HANDLING GET REQUESTS
A call to
.Fn getcb
must eventually result in a call to one of the following functions:
.Bl -tag -width agentx_varbind_counter32()
.It Fn agentx_varbind_integer
Set the return value to an int32_t value.
.It Fn agentx_varbind_string
A C string wrapper around
.Fn agentx_varbind_nstring .
.It Fn agentx_varbind_nstring
Set the return value to an octetstring.
.It Fn agentx_varbind_printf
A printf wrapper around
.Fn agentx_varbind_nstring .
.It Fn agentx_varbind_null
Set the return value to null.
.It Fn agentx_varbind_oid
Set the return value to an OID value.
.It Fn agentx_varbind_object
An agentx_object wrapper around
.Fn agentx_varbind_oid .
.It Fn agentx_varbind_index
An agentx_index wrapper around
.Fn agentx_varbind_oid .
.It Fn agentx_varbind_ipaddress
Set the return value to ipaddress.
.It Fn agentx_varbind_counter32
Set the return value to an uint32_t of type counter32.
.It Fn agentx_varbind_gauge32
Set the return value to an uint32_t of type gauge32.
.It Fn agentx_varbind_unsigned32
A wrapper around agentx_varbind_gauge32.
.It Fn agentx_varbind_timeticks
Set the return value to an uint32_t of type timeticks.
.It Fn agentx_varbind_opaque
Set the return value to an opaque value.
.It Fn agentx_varbind_counter64
Set the return value to an uint64_t of type counter64.
.It Fn agentx_varbind_notfound
When the request is of type GET, return a nosuchinstance error.
When the request is of type GETNEXT or GETBULK, return an endofmibview error.
On endofmibview the next object is queried.
This function can only be called on objects that contain one or more *_dynamic
indices.
.It Fn agentx_varbind_error
Returns a GENERR error to the client.
.El
.Pp
For objects containing *_dynamic indices the following support functions are to
be used:
.Bl -tag -width Ds
.It Fn agentx_varbind_request
Returns whether the request is of type GET, GETNEXT or GETNEXTINCLUSIVE.
.It Fn agentx_varbind_get_index_integer
Retrieve a single int32_t index value.
.It Fn agentx_varbind_get_index_string
Retrieve an octetstring index value.
.Fa slen
is the length of the string and
.Fa implied
indicates if the next value for this index should be length sorted before
alphabetically sorted.
.It Fn agentx_varbind_get_index_oid
Retrieve an oid index value.
.Fa oidlen
is the length of the oid and
.Fa implied
indicates if the next value for this index should be length sorted before
alphabetically sorted.
.It Fn agentx_varbind_get_index_ipaddress
Retrieve an ipaddress index value.
.It Fn agentx_varbind_set_index_integer
Sets a single int32_t index value.
.It Fn agentx_varbind_set_index_string
A C string wrapper around
.Fn agentx_varbind_set_index_nstring .
.It Fn agentx_varbind_set_index_nstring
Set an octetstring index value.
.It Fn agentx_varbind_set_index_oid
Set an oid index value.
.It Fn agentx_varbind_set_index_object
A agentx_object wrapper around
.Fn agentx_varbind_set_index_oid .
.It Fn agentx_varbind_set_index_ipaddress
Set an ipaddress index value.
.El
.Pp
For these functions
.Fa sai
must be part of the object the request is performed on.
The function type must also match the data type of
.Fa sai .
.Pp
Other functions that can retrieve information from the agentx context are:
.Bl -tag -width Ds
.It Fn agentx_context_object_find
Find an agentx_object created inside agentx_context
.Fa sac
based on
.Fa oid
and
.Fa oidlen .
If
.Fa active
is set the object must be reachable from the agentx master, else NULL is
returned.
If
.Fa oid
can be an instance, find its parent object.
.It Fn agentx_context_object_nfind
Find the next agentx_object created inside agentx_context
.Fa sac
based on
.Fa oid
and
.Fa oidlen .
If
.Fa active
is set the object must be reachable from the agentx master, else NULL is
returned.
If
.Fa inclusive
is set, the object returned may also exactly match
.Fa oid .
.It Fn agentx_context_uptime
Returns the sysuptime in seconds for
.Fa sac
in timeticks.
.El
.Sh SEE ALSO
.Xr snmp 1 ,
.Xr snmpd 8
.Sh STANDARDS
.Rs
.%A M. Daniele
.%A B. Wijnen
.%A M. Ellison, Ed.
.%A D. Francisco, Ed.
.%D January 2000
.%R RFC 2741
.%T Agent Extensibility (AgentX) Protocol Version 1
.Re
.Pp
.Rs
.%A L. Heintz
.%A S. Gudur
.%A M. Ellison, Ed.
.%D January 2000
.%R RFC 2742
.%T Definitions of Managed Objects for Extensible SNMP Agents
.Re
.Sh HISTORY
The
.Nm agentx
API first appeared in
.Ox 6.9 .
.Sh AUTHORS
.An Martijn van Duren Aq Mt martijn@openbsd.org