keyctl_capabilities(3) — Linux manual page



NAME         top

       keyctl_capabilities - Query subsystem capabilities

SYNOPSIS         top

       #include <keyutils.h>

       long keyctl_capabilities(unsigned char *buffer, size_t buflen);

DESCRIPTION         top

       keyctl_capabilities() queries the keyrings subsystem in the kernel to
       ask about its capabilities and fills in the array in the buffer with
       bits that indicate the presence or absence of specific features in
       the keyrings subsystem.

       The function returns the amount of data the kernel has available,
       irrespective of the amount of buffer space available.  If the buffer
       is shorter than the data, a short copy will be made; if the buffer is
       larger than the data, the excess space will be cleared.

       If this operation is not available in the kernel, the keyutils
       library will emulate it as best it can and the capability bit that
       indicates if the kernel operation is available will be cleared.

       In buffer[0], the following capabilities exist:

              This is set if the kernel supports this operation and cleared
              otherwise.  If it is cleared, the rest of the flags are

              This is set if the kernel supports persistent keyrings and
              cleared otherwise.  See keyctl_get_persistent(3).

              This is set if the kernel supports Diffie-Hellman calculation
              and cleared otherwise.  See keyctl_dh_compute(3).

              This is set if the kernel supports public-key operations and
              cleared otherwise.  See keyctl_pkey_query(3).

              This is set if the kernel supports the big_key key type and
              cleared otherwise.

              This is set if the kernel supports key invalidation and
              cleared otherwise.  See keyctl_invalidate(3).

              This is set if the kernel supports restrictions on keyrings
              and cleared otherwise.  See keyctl_restrict_keyring(3).

              This is set if the kernel supports the move key operation and
              cleared otherwise.  See keyctl_move(3).

       In buffer[1], the following capabilities exist:

              This is set if the keyring names are segregated according to
              the user-namespace in which a keyring is created.

              This is set if a key or keyring may get tagged with a
              namespace, thereby allowing multiple keys with the same type
              and description, but different namespace tags, to coexist
              within the same keyring.  Tagging may be automatic depending
              on the key type.  Only network-namespace tagging is currently

RETURN VALUE         top

       On success keyctl_capabilities() returns the size of the data it has
       available, irrespective of the size of the buffer.  On error, the
       value -1 will be returned and errno will have been set to an
       appropriate error.

ERRORS         top

       EFAULT The buffer cannot be written to.

LINKING         top

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

SEE ALSO         top

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

COLOPHON         top

       This page is part of the keyutils (key management utilities) project.
       Information about the project can be found at [unknown -- if you
       know, please contact] If you have a bug report for
       this manual page, send it to  This page was
       obtained from the project's upstream Git repository
       on 2020-08-13.  (At that time, the date of the most recent commit
       that was found in the repository was 2020-07-07.)  If you discover
       any rendering problems in this HTML version of the page, or you
       believe there is a better or more up-to-date source for the page, or
       you have corrections or improvements to the information in this
       COLOPHON (which is not part of the original manual page), send a mail

Linux                            30 May 2019          KEYCTL_CAPABILITIES(3)

Pages that refer to this page: keyctl(3)