#include <keyutils.h>

       key_serial_t request_key(const char *type, const char *description,
                                const char *callout_info,
                                key_serial_t keyring);

       request_key()  asks  the  kernel  to  find a key of the given type that
       matches the specified description and, if successful, to attach  it  to
       the nominated keyring and to return its serial number.

       request_key()  first  recursively searches all the keyrings attached to
       the calling process in the order thread-specific keyring,  process-spe-
       cific keyring and then session keyring for a matching key.

       If  request_key()  is called from a program invoked by request_key() on
       behalf of some other process to generate a key, then  the  keyrings  of
       that  other  process  will be searched next, using that other process's
       UID, GID, groups, and security context to control access.

       The keys in each keyring searched are checked for a  match  before  any
       child  keyrings  are  recursed into.  Only keys that are searchable for
       the caller may be found, and only searchable keyrings may be searched.

       If the key is not found, then, if callout_info is  set,  this  function
       will  attempt to look further afield.  In such a case, the callout_info
       is passed to a user-space service such as /sbin/request-key to generate
       the key.

       If  that  is  unsuccessful  also, then an error will be returned, and a
       temporary negative key will be  installed  in  the  nominated  keyring.
       This  will  expire after a few seconds, but will cause subsequent calls
       to request_key() to fail until it does.

       The keyring serial number may be that of a valid keyring to  which  the
       caller has write permission, or it may be a special keyring ID:

              This specifies the caller's thread-specific keyring.

              This specifies the caller's process-specific keyring.

              This specifies the caller's session-specific keyring.

              This specifies the caller's UID-specific keyring.

              This specifies the caller's UID-session keyring.

       If  a  key is created, no matter whether it's a valid key or a negative
       key, it will displace any other key of the same  type  and  description
       EDQUOT The  key  quota for this user would be exceeded by creating this
              key or linking it to the keyring.

              An expired key was found, but no replacement could be obtained.

              The attempt to generate a new key was rejected.

              A revoked key was found, but no replacement could be obtained.

       ENOMEM Insufficient memory to create a key.

       ENOKEY No matching key was found.

       Although this is a Linux system call, it is not present in libc but can
       be  found  rather  in  libkeyutils.  When linking, -lkeyutils should be
       specified to the linker.

       keyctl(1),  add_key(2),  keyctl(2),  keyctl(3),  keyrings(7),  request-

       This  page  is  part of release 4.04 of the Linux man-pages project.  A
       description of the project, information about reporting bugs,  and  the
       latest     version     of     this    page,    can    be    found    at

Linux                             2015-05-07                    REQUEST_KEY(2)
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