NAME

       keyctl_read - read a key

SYNOPSIS

       #include <keyutils.h>

       long keyctl_read(key_serial_t key, char *buffer, size_t buflen);

       long keyctl_read_alloc(key_serial_t key, void **_buffer);

DESCRIPTION

       keyctl_read() reads the payload of a key if the key type supports it.

       The caller must have read permission on a key to be able to read it.

       buffer  and  buflen  specify the buffer into which the payload data will be placed.  If the buffer is too
       small, then the full size of the payload will be  returned,  and  the  contents  of  the  buffer  may  be
       overwritten in some undefined way.

       keyctl_read_alloc()  is similar to 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  *_buffer.
       The caller must free the buffer.

       keyctl_read_alloc()  adds  a NUL character after the data it retrieves, though this is not counted in the
       size value it returns.

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 key_serial_t values, each of which corresponds to a key to which the keyring holds a link.

       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.

RETURN VALUE

       On success 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,  and  the  contents  of  the  buffer  may  have  been
       overwritten in some undefined way.

       On success keyctl_read_alloc() returns the amount of data in the buffer.

       On error, both functions set errno to an appropriate code and return the value -1.

ERRORS

       ENOKEY The key specified is invalid.

       EKEYEXPIRED
              The key specified has expired.

       EKEYREVOKED
              The key specified had been revoked.

       EACCES The key exists, but is not readable by the calling process.

       EOPNOTSUPP
              The key type does not support reading of the payload data.

LINKING

       This  is  a  library  function  that  can  be  found  in libkeyutils.  When linking, -lkeyutils should be
       specified to the linker.

SEE ALSO

       keyctl(1), add_key(2), keyctl(2), request_key(2), keyctl(3), keyrings(7), keyutils(7)