1. 根目录:
2. arch
3. x86
4. um
5. asm
6. segment.h

#ifndef __UM_SEGMENT_H
#define __UM_SEGMENT_H

extern int host_gdt_entry_tls_min;

#define GDT_ENTRY_TLS_ENTRIES 3
#define GDT_ENTRY_TLS_MIN host_gdt_entry_tls_min
#define GDT_ENTRY_TLS_MAX (GDT_ENTRY_TLS_MIN + GDT_ENTRY_TLS_ENTRIES - 1)

typedef struct {
	unsigned long seg;
} mm_segment_t;

#define MAKE_MM_SEG(s)	((mm_segment_t) { (s) })
#define KERNEL_DS	MAKE_MM_SEG(~0UL)
#define USER_DS		MAKE_MM_SEG(TASK_SIZE)

#endif