man/keyctl_read.3

.\"
.\" Copyright (C) 2006 Red Hat, Inc. All Rights Reserved.
.\" Written by David Howells (dhowells@redhat.com)
.\"
.\" This program is free software; you can redistribute it and/or
.\" modify it under the terms of the GNU General Public License
.\" as published by the Free Software Foundation; either version
.\" 2 of the License, or (at your option) any later version.
.\"
.TH KEYCTL_READ 3 "21 Feb 2014" Linux "Linux Key Management Calls"
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.SH NAME
keyctl_read \- read a key
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.SH SYNOPSIS
.nf
.B #include <keyutils.h>
.sp
.BI "long keyctl_read(key_serial_t " key ", char *" buffer ,
.BI "size_t" buflen ");"
.sp
.BI "long keyctl_read_alloc(key_serial_t " key ", void **" _buffer ");"
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.SH DESCRIPTION
.BR keyctl_read ()
reads the payload of a key if the key type supports it.
.P
The caller must have
.B read
permission on a key to be able to read it.
.P
.I buffer
and
.I buflen
specify the buffer into which the payload data will be placed.  If the buffer
is too small, the full size of the payload will be returned and no copy will
take place.
.P
.BR keyctl_read_alloc ()
is similar to
.BR keyctl_read ()
except that it allocates a buffer big enough to hold the payload data and
places the data in it.  If successful, a pointer to the buffer is placed in
.IR *_buffer .
The caller must free the buffer.
.P
.BR keyctl_read_alloc ()
adds a NUL character after the data it retrieves, though this is not counted
in the size value it returns.
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.SH READING KEYRINGS
This call can be used to list the contents of a keyring.  The data is
presented to the user as an array of
.B key_serial_t
values, each of which corresponds to a key to which the keyring holds a link.
.P
The size of the keyring will be sizeof(key_serial_t) multiplied by the number
of keys.  The size of key_serial_t is invariant across different word sizes,
though the byte-ordering is as appropriate for the kernel.
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.SH RETURN VALUE
On success
.BR keyctl_read ()
returns the amount of data placed into the buffer.  If the buffer was too
small, then the size of buffer required will be returned, but no data will be
transferred.
.P
On success
.BR keyctl_read_alloc ()
returns the amount of data in the buffer.
.P
On error, both functions set
.I errno
to an appropriate code and return the value
.BR -1 .
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.SH ERRORS
.TP
.B ENOKEY
The key specified is invalid.
.TP
.B EKEYEXPIRED
The key specified has expired.
.TP
.B EKEYREVOKED
The key specified had been revoked.
.TP
.B EACCES
The key exists, but is not
.B readable
by the calling process.
.TP
.B EOPNOTSUPP
The key type does not support reading of the payload data.
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.SH LINKING
This is a library function that can be found in
.IR libkeyutils .
When linking,
.B -lkeyutils
should be specified to the linker.
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.SH SEE ALSO
.ad l
.nh
.BR keyctl (1),
.BR add_key (2),
.BR keyctl (2),
.BR request_key (2),
.BR keyctl (3),
.BR keyrings (7),
.BR keyutils (7)