.TH mtcp_get_uctx 3 2017-02-02 "Linux" "mOS Library Functions Manual"
.SH NAME
mtcp_get_uctx \- get private per-flow user-context data
.SH SYNOPSIS
.B #include <mos_api.h>
.sp
.BI "int mtcp_get_uctx(mctx_t " mctx ", int " sockid );

.SH DESCRIPTION
.BR mtcp_get_uctx () 
can be used to retrieve flow-specific monitoring data to
a flow record in the application layer. It is generally used
in tandem with
.BR mtcp_set_uctx () .
The flow-specific data is stored with the socket that can
referred to by the
.I "sockid"
argument.
The private data can be stored as a void *. It is the
responsibility of the user to free up the private data (if it
is dynamically allocated from memory) when the flow
record gets deleted from the stack (due to, e.g., connection
termination).

The 
.BR mtcp_get_uctx ()
call takes an additional argument named 
.I "mctx"
that represents the per-core mTCP context in an application
(see
.BR mtcp_create_context()
for details).
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.SH RETURN VALUE
Returns pointer to the private data as void * on success; NULL on failure. In case
of failure,
.I "errno"
is set appropriately.
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.SH ERRORS
.TP 10
.B "EACCES"
.I "mctx"
is not a valid.

.TP 10
.B "EBADF"
.I "sockid"
is not a valid socket descriptor for binding to an address.

.TP 10
.B "EPERM"
The user does not have permission to access the data.
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.\""""".SH CONFORMING TO
.\"""""POSIX.1-2001.
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.SH AUTHORS
mOS development team <mtcp-user@list.ndsl.kaist.edu>
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.SH SEE ALSO
.BR mtcp_socket (),
.BR mtcp_set_uctx (),
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.SH COLOPHON
This page is part of mOS release 0.3
.I "docs"
section. A description of the project, and information
about reporting bugs, can be found at
\%http://mos.kaist.edu/.
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