#include <sys/types.h>int modify_ldt(int func, void *ptr, unsigned long bytecount);
DESCRIPTION
modify_ldt()
reads or writes the local descriptor table (ldt) for a process.
The ldt is a per-process memory management table used by the i386 processor.
For more information on this table, see an Intel 386 processor handbook.
When
func
is 0,
modify_ldt()
reads the ldt into the memory pointed to by
ptr.
The number of bytes read is the smaller of
bytecount
and the actual size of the ldt.
When
func
is 1,
modify_ldt()
modifies one ldt entry.
ptr
points to a
user_desc
structure
and
bytecount
must equal the size of this structure.
The
user_desc
structure is defined in <asm/ldt.h> as:
struct user_desc {
unsigned int entry_number;
unsigned long base_addr;
unsigned int limit;
unsigned int seg_32bit:1;
unsigned int contents:2;
unsigned int read_exec_only:1;
unsigned int limit_in_pages:1;
unsigned int seg_not_present:1;
unsigned int useable:1;
};
In Linux 2.4 and earlier, this structure was named
modify_ldt_ldt_s.
RETURN VALUE
On success,
modify_ldt()
returns either the actual number of bytes read (for reading)
or 0 (for writing).
On failure,
modify_ldt()
returns -1 and sets
errno
to indicate the error.
ERRORS
EFAULT
ptr
points outside the address space.
EINVAL
ptr
is 0,
or
func
is 1 and
bytecount
is not equal to the size of the structure
modify_ldt_ldt_s,
or
func
is 1 and the new ldt entry has invalid values.
ENOSYS
func
is neither 0 nor 1.
CONFORMING TO
This call is Linux-specific and should not be used in programs intended
to be portable.
NOTES
Glibc does not provide a wrapper for this system call; call it using
syscall(2).
This page is part of release 3.14 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
