dl_data_req.7

7号信令功能代码,为开源代码

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.TH DL_DATA_REQ 7 "2004/01/12 23:45:11" "LiS-2_16_18-8" "Linux STREAMS"
.SH NAME
.B DL_DATA_REQ
\- conveys a complete DLSDU from the DLS user to the DLS provider for
transmission over the data link connection.
.SH SYNOPSIS
The message consists of one or more
.B M_DATA
message blocks containing at least one byte of data.
.SH DECRIPTION
To simplify the support of a
.BR read (2)/ write (2)
interface to the data link layer, the DLS provider must recognize and process
messages that consist of one or more
.B M_DATA
message blocks with non preceding
.B M_PROTO
message block.  This message type may originate from the
.BR write (2)
system call.
.PP
This does not imply that DLPI will directly support a pure
.BR read (2)/ write (2).
If such an interface is desired, a STREAMS module could be implemented to be
pushed above the DLS provider.
.SH STATE
The message is valid in state
.BR DL_DATAXFER .
If it is received in state
.BR DL_IDLE " or " DL_PROV_RESET_PENDING ,
it should be discarded without generating an error.
.SH "NEW STATE"
The resulting state is unchanged.
.SH RESPONSE
If the request is valid, no response is generated.
.PP
If the request is erroneous, a STREAMS
.B M_ERROR
message should be issued to the DLS user specifying an
.IR errno (3)
value of
.BR EPROTO .
This action should be interpreted as a fatal, unrecoverable, protocol error.
A request is considered erroneous under the following conditions:
.IP \(em 4
The primitive was issued from an invalid state.  If the request is issued in
state
.BR DL_IDLE " or " DL_PROV_RESET_PENDING ,
however,
it is silently discarded with no fatal error generated.
.IP \(em
The amount of data in the current DLSDU is not within the DLS provider's
acceptable bounds as spcified by
.IR dl_min_sdu " and " dl_max_sdu
in the
.BR DL_INFO_ACK (7).
.SH NOTES
A STREAMS module would implement "more" field processing itself to support
direct user-level access.  This module could collect messages and send them in
one larger message to the DLS provider, or break large DLSDUs passed to the
DLS user into smaller messages.  The module would only be pushed if the DLS
user was a user-level process.
.SH VERSIONS
.PP
This manpage was written for
.B LiS\c
.
.[
LiS
.]
.br
The Data Link Provider Interface first appeared in SVR 4.
.[
svr4
.]
.br
This interface conforms to DLPI Revision 2.
.XX
.[
dlpi
.]
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magic
.]
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advprog
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$LIST$
.]
.T2