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-.\" Copyright (C) 2016 Intel Corporation
-.\"
-.\" SPDX-License-Identifier: Linux-man-pages-copyleft
-.\"
-.TH pkey_alloc 2 (date) "Linux man-pages (unreleased)"
-.SH NAME
-pkey_alloc, pkey_free \- allocate or free a protection key
-.SH LIBRARY
-Standard C library
-.RI ( libc ", " \-lc )
-.SH SYNOPSIS
-.nf
-.BR "#define _GNU_SOURCE" " /* See feature_test_macros(7) */"
-.B #include <sys/mman.h>
-.P
-.BI "int pkey_alloc(unsigned int " flags ", unsigned int " access_rights ");"
-.BI "int pkey_free(int " pkey ");"
-.fi
-.SH DESCRIPTION
-.BR pkey_alloc ()
-allocates a protection key (pkey) and allows it to be passed to
-.BR pkey_mprotect (2).
-.P
-The
-.BR pkey_alloc ()
-.I flags
-is reserved for future use and currently must always be specified as 0.
-.P
-The
-.BR pkey_alloc ()
-.I access_rights
-argument may contain zero or more disable operations:
-.TP
-.B PKEY_DISABLE_ACCESS
-Disable all data access to memory covered by the returned protection key.
-.TP
-.B PKEY_DISABLE_WRITE
-Disable write access to memory covered by the returned protection key.
-.P
-.BR pkey_free ()
-frees a protection key and makes it available for later
-allocations.
-After a protection key has been freed, it may no longer be used
-in any protection-key-related operations.
-.P
-An application should not call
-.BR pkey_free ()
-on any protection key which has been assigned to an address
-range by
-.BR pkey_mprotect (2)
-and which is still in use.
-The behavior in this case is undefined and may result in an error.
-.SH RETURN VALUE
-On success,
-.BR pkey_alloc ()
-returns a positive protection key value.
-On success,
-.BR pkey_free ()
-returns zero.
-On error, \-1 is returned, and
-.I errno
-is set to indicate the error.
-.SH ERRORS
-.TP
-.B EINVAL
-.IR pkey ,
-.IR flags ,
-or
-.I access_rights
-is invalid.
-.TP
-.B ENOSPC
-.RB ( pkey_alloc ())
-All protection keys available for the current process have
-been allocated.
-The number of keys available is architecture-specific and
-implementation-specific and may be reduced by kernel-internal use
-of certain keys.
-There are currently 15 keys available to user programs on x86.
-.IP
-This error will also be returned if the processor or operating system
-does not support protection keys.
-Applications should always be prepared to handle this error, since
-factors outside of the application's control can reduce the number
-of available pkeys.
-.SH STANDARDS
-Linux.
-.SH HISTORY
-Linux 4.9,
-glibc 2.27.
-.SH NOTES
-.BR pkey_alloc ()
-is always safe to call regardless of whether or not the operating system
-supports protection keys.
-It can be used in lieu of any other mechanism for detecting pkey support
-and will simply fail with the error
-.B ENOSPC
-if the operating system has no pkey support.
-.P
-The kernel guarantees that the contents of the hardware rights
-register (PKRU) will be preserved only for allocated protection
-keys.
-Any time a key is unallocated (either before the first call
-returning that key from
-.BR pkey_alloc ()
-or after it is freed via
-.BR pkey_free ()),
-the kernel may make arbitrary changes to the parts of the
-rights register affecting access to that key.
-.SH EXAMPLES
-See
-.BR pkeys (7).
-.SH SEE ALSO
-.BR pkey_mprotect (2),
-.BR pkeys (7)