Linux Audio

Check our new training course

Embedded Linux Audio

Check our new training course
with Creative Commons CC-BY-SA
lecture materials

Bootlin logo

Elixir Cross Referencer

Loading...
  1
  2
  3
  4
  5
  6
  7
  8
  9
 10
 11
 12
 13
 14
 15
 16
 17
 18
 19
 20
 21
 22
 23
 24
 25
 26
 27
 28
 29
 30
 31
 32
 33
 34
 35
 36
 37
 38
 39
 40
 41
 42
 43
 44
 45
 46
 47
 48
 49
 50
 51
 52
 53
 54
 55
 56
 57
 58
 59
 60
 61
 62
 63
 64
 65
 66
 67
 68
 69
 70
 71
 72
 73
 74
 75
 76
 77
 78
 79
 80
 81
 82
 83
 84
 85
 86
 87
 88
 89
 90
 91
 92
 93
 94
 95
 96
 97
 98
 99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
219
220
221
222
223
224
225
226
227
228
229
230
231
232
233
234
235
236
237
238
239
240
241
242
243
244
245
246
247
248
249
250
251
252
253
254
255
256
257
258
259
260
261
262
263
264
265
266
267
268
269
270
271
272
273
274
275
276
277
278
279
280
281
282
283
284
285
286
287
288
289
290
291
292
293
294
295
296
297
298
299
300
301
302
303
304
305
306
307
308
309
310
311
312
313
314
315
316
317
318
319
320
321
322
323
324
325
326
327
328
329
330
331
332
333
334
335
336
337
338
339
340
341
342
343
344
345
346
347
348
349
350
351
352
353
354
355
356
357
358
359
360
361
362
363
364
365
366
367
368
369
370
371
372
373
374
375
376
377
378
379
380
381
382
383
384
385
386
387
388
389
390
391
392
393
394
395
396
397
398
399
400
401
402
403
404
405
406
407
408
409
410
411
412
413
414
415
416
417
418
419
420
421
422
423
424
425
426
427
428
429
430
431
432
433
434
435
436
437
438
439
440
441
442
443
444
445
446
447
448
449
450
451
452
453
454
455
456
457
458
459
460
461
462
463
464
465
466
467
468
469
470
471
472
473
474
475
476
477
478
479
480
481
482
483
484
485
486
487
488
489
490
491
492
493
494
495
496
497
498
499
500
501
502
503
504
505
506
507
508
509
510
511
512
513
514
515
516
517
518
519
520
521
522
523
524
525
526
527
528
529
530
531
532
533
534
535
536
537
538
539
540
541
542
543
544
545
546
547
548
549
550
551
552
553
554
555
556
557
558
559
560
561
562
563
564
565
566
567
568
569
570
571
572
573
574
575
576
577
578
579
580
581
582
583
584
585
586
587
588
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613
614
615
616
617
618
619
620
621
622
623
624
625
626
627
628
629
630
631
632
633
634
635
636
637
638
639
640
641
642
643
644
645
646
647
648
649
650
651
652
653
654
655
656
657
658
659
660
661
662
663
664
665
666
667
668
669
670
671
672
673
674
675
676
677
678
679
680
681
682
683
684
685
686
687
688
689
690
691
692
693
694
695
696
697
698
699
700
701
702
703
704
705
706
707
708
709
710
711
712
713
714
715
716
717
718
719
720
721
722
723
724
725
726
727
728
729
730
731
732
733
734
735
736
737
738
739
740
741
742
743
744
745
746
747
748
749
750
751
752
753
754
755
756
757
758
759
760
761
762
763
764
765
766
767
768
769
770
771
772
773
774
775
776
777
778
779
780
781
782
783
784
785
786
787
788
789
790
791
792
793
794
795
796
797
798
799
800
801
802
803
804
805
806
807
808
809
810
811
812
813
814
815
816
817
818
819
820
821
822
823
824
825
826
827
828
829
830
831
832
833
834
835
836
837
838
839
840
841
842
843
844
845
846
847
848
849
850
851
852
853
854
855
856
857
858
859
860
861
862
863
864
865
866
867
868
869
870
871
872
873
874
875
876
877
878
/*
 *	linux/mm/mmap.c
 *
 * Written by obz.
 */
#include <linux/slab.h>
#include <linux/shm.h>
#include <linux/mman.h>
#include <linux/pagemap.h>
#include <linux/swap.h>
#include <linux/swapctl.h>
#include <linux/smp_lock.h>
#include <linux/init.h>
#include <linux/file.h>

#include <asm/uaccess.h>
#include <asm/pgtable.h>

/* description of effects of mapping type and prot in current implementation.
 * this is due to the limited x86 page protection hardware.  The expected
 * behavior is in parens:
 *
 * map_type	prot
 *		PROT_NONE	PROT_READ	PROT_WRITE	PROT_EXEC
 * MAP_SHARED	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
 *		w: (no) no	w: (no) no	w: (yes) yes	w: (no) no
 *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
 *		
 * MAP_PRIVATE	r: (no) no	r: (yes) yes	r: (no) yes	r: (no) yes
 *		w: (no) no	w: (no) no	w: (copy) copy	w: (no) no
 *		x: (no) no	x: (no) yes	x: (no) yes	x: (yes) yes
 *
 */
pgprot_t protection_map[16] = {
	__P000, __P001, __P010, __P011, __P100, __P101, __P110, __P111,
	__S000, __S001, __S010, __S011, __S100, __S101, __S110, __S111
};

/* SLAB cache for vm_area_struct's. */
kmem_cache_t *vm_area_cachep;

int sysctl_overcommit_memory;

/* Check that a process has enough memory to allocate a
 * new virtual mapping.
 */
int vm_enough_memory(long pages)
{
	/* Stupid algorithm to decide if we have enough memory: while
	 * simple, it hopefully works in most obvious cases.. Easy to
	 * fool it, but this should catch most mistakes.
	 */
	/* 23/11/98 NJC: Somewhat less stupid version of algorithm,
	 * which tries to do "TheRightThing".  Instead of using half of
	 * (buffers+cache), use the minimum values.  Allow an extra 2%
	 * of num_physpages for safety margin.
	 */

	long free;
	
        /* Sometimes we want to use more memory than we have. */
	if (sysctl_overcommit_memory)
	    return 1;

	free = buffermem >> PAGE_SHIFT;
	free += page_cache_size;
	free += nr_free_pages;
	free += nr_swap_pages;
	free -= (page_cache.min_percent + buffer_mem.min_percent + 2)*num_physpages/100; 
	return free > pages;
}

/* Remove one vm structure from the inode's i_mmap ring. */
static inline void remove_shared_vm_struct(struct vm_area_struct *vma)
{
	struct file * file = vma->vm_file;

	if (file) {
		if (vma->vm_flags & VM_DENYWRITE)
			file->f_dentry->d_inode->i_writecount++;
		if(vma->vm_next_share)
			vma->vm_next_share->vm_pprev_share = vma->vm_pprev_share;
		*vma->vm_pprev_share = vma->vm_next_share;
	}
}

asmlinkage unsigned long sys_brk(unsigned long brk)
{
	unsigned long rlim, retval;
	unsigned long newbrk, oldbrk;
	struct mm_struct *mm = current->mm;

	down(&mm->mmap_sem);

	/*
	 * This lock-kernel is one of the main contention points for
	 * certain normal loads.  And it really should not be here: almost
	 * everything in brk()/mmap()/munmap() is protected sufficiently by
	 * the mmap semaphore that we got above.
	 *
	 * We should move this into the few things that really want the
	 * lock, namely anything that actually touches a file descriptor
	 * etc.  We can do all the normal anonymous mapping cases without
	 * ever getting the lock at all - the actual memory management
	 * code is already completely thread-safe.
	 */
	lock_kernel();

	if (brk < mm->end_code)
		goto out;
	newbrk = PAGE_ALIGN(brk);
	oldbrk = PAGE_ALIGN(mm->brk);
	if (oldbrk == newbrk)
		goto set_brk;

	/* Always allow shrinking brk. */
	if (brk <= mm->brk) {
		if (!do_munmap(newbrk, oldbrk-newbrk))
			goto set_brk;
		goto out;
	}

	/* Check against rlimit and stack.. */
	rlim = current->rlim[RLIMIT_DATA].rlim_cur;
	if (rlim < RLIM_INFINITY && brk - mm->end_code > rlim)
		goto out;

	/* Check against existing mmap mappings. */
	if (find_vma_intersection(mm, oldbrk, newbrk+PAGE_SIZE))
		goto out;

	/* Check if we have enough memory.. */
	if (!vm_enough_memory((newbrk-oldbrk) >> PAGE_SHIFT))
		goto out;

	/* Ok, looks good - let it rip. */
	if (do_mmap(NULL, oldbrk, newbrk-oldbrk,
		   PROT_READ|PROT_WRITE|PROT_EXEC,
		   MAP_FIXED|MAP_PRIVATE, 0) != oldbrk)
		goto out;
set_brk:
	mm->brk = brk;
out:
	retval = mm->brk;
	unlock_kernel();
	up(&mm->mmap_sem);
	return retval;
}

/* Combine the mmap "prot" and "flags" argument into one "vm_flags" used
 * internally. Essentially, translate the "PROT_xxx" and "MAP_xxx" bits
 * into "VM_xxx".
 */
static inline unsigned long vm_flags(unsigned long prot, unsigned long flags)
{
#define _trans(x,bit1,bit2) \
((bit1==bit2)?(x&bit1):(x&bit1)?bit2:0)

	unsigned long prot_bits, flag_bits;
	prot_bits =
		_trans(prot, PROT_READ, VM_READ) |
		_trans(prot, PROT_WRITE, VM_WRITE) |
		_trans(prot, PROT_EXEC, VM_EXEC);
	flag_bits =
		_trans(flags, MAP_GROWSDOWN, VM_GROWSDOWN) |
		_trans(flags, MAP_DENYWRITE, VM_DENYWRITE) |
		_trans(flags, MAP_EXECUTABLE, VM_EXECUTABLE);
	return prot_bits | flag_bits;
#undef _trans
}

unsigned long do_mmap(struct file * file, unsigned long addr, unsigned long len,
	unsigned long prot, unsigned long flags, unsigned long off)
{
	struct mm_struct * mm = current->mm;
	struct vm_area_struct * vma;
	int error;

	if (file && (!file->f_op || !file->f_op->mmap))
		return -ENODEV;

	if ((len = PAGE_ALIGN(len)) == 0)
		return addr;

	if (len > TASK_SIZE || addr > TASK_SIZE-len)
		return -EINVAL;

	/* offset overflow? */
	if (off + len - 1 < off)
		return -EINVAL;

	/* Too many mappings? */
	if (mm->map_count > MAX_MAP_COUNT)
		return -ENOMEM;

	/* mlock MCL_FUTURE? */
	if (mm->def_flags & VM_LOCKED) {
		unsigned long locked = mm->locked_vm << PAGE_SHIFT;
		locked += len;
		if ((current->rlim[RLIMIT_MEMLOCK].rlim_cur < RLIM_INFINITY) &&
		   (locked > current->rlim[RLIMIT_MEMLOCK].rlim_cur))
			return -EAGAIN;
	}

	/* Do simple checking here so the lower-level routines won't have
	 * to. we assume access permissions have been handled by the open
	 * of the memory object, so we don't do any here.
	 */
	if (file != NULL) {
		switch (flags & MAP_TYPE) {
		case MAP_SHARED:
			if ((prot & PROT_WRITE) && !(file->f_mode & 2))
				return -EACCES;

			/* Make sure we don't allow writing to an append-only file.. */
			if (IS_APPEND(file->f_dentry->d_inode) && (file->f_mode & 2))
				return -EACCES;

			/* make sure there are no mandatory locks on the file. */
			if (locks_verify_locked(file->f_dentry->d_inode))
				return -EAGAIN;

			/* fall through */
		case MAP_PRIVATE:
			if (!(file->f_mode & 1))
				return -EACCES;
			break;

		default:
			return -EINVAL;
		}
	} else if ((flags & MAP_TYPE) != MAP_PRIVATE)
		return -EINVAL;

	/* Obtain the address to map to. we verify (or select) it and ensure
	 * that it represents a valid section of the address space.
	 */
	if (flags & MAP_FIXED) {
		if (addr & ~PAGE_MASK)
			return -EINVAL;
	} else {
		addr = get_unmapped_area(addr, len);
		if (!addr)
			return -ENOMEM;
	}

	/* Determine the object being mapped and call the appropriate
	 * specific mapper. the address has already been validated, but
	 * not unmapped, but the maps are removed from the list.
	 */
	vma = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
	if (!vma)
		return -ENOMEM;

	vma->vm_mm = mm;
	vma->vm_start = addr;
	vma->vm_end = addr + len;
	vma->vm_flags = vm_flags(prot,flags) | mm->def_flags;

	if (file) {
		if (file->f_mode & 1)
			vma->vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
		if (flags & MAP_SHARED) {
			vma->vm_flags |= VM_SHARED | VM_MAYSHARE;

			/* This looks strange, but when we don't have the file open
			 * for writing, we can demote the shared mapping to a simpler
			 * private mapping. That also takes care of a security hole
			 * with ptrace() writing to a shared mapping without write
			 * permissions.
			 *
			 * We leave the VM_MAYSHARE bit on, just to get correct output
			 * from /proc/xxx/maps..
			 */
			if (!(file->f_mode & 2))
				vma->vm_flags &= ~(VM_MAYWRITE | VM_SHARED);
		}
	} else
		vma->vm_flags |= VM_MAYREAD | VM_MAYWRITE | VM_MAYEXEC;
	vma->vm_page_prot = protection_map[vma->vm_flags & 0x0f];
	vma->vm_ops = NULL;
	vma->vm_offset = off;
	vma->vm_file = NULL;
	vma->vm_pte = 0;

	/* Clear old maps */
	error = -ENOMEM;
	if (do_munmap(addr, len))
		goto free_vma;

	/* Check against address space limit. */
	if ((current->rlim[RLIMIT_AS].rlim_cur < RLIM_INFINITY) &&
	    ((mm->total_vm << PAGE_SHIFT) + len
	    > current->rlim[RLIMIT_AS].rlim_cur))
		goto free_vma;

	/* Private writable mapping? Check memory availability.. */
	if ((vma->vm_flags & (VM_SHARED | VM_WRITE)) == VM_WRITE &&
	    !(flags & MAP_NORESERVE)				 &&
	    !vm_enough_memory(len >> PAGE_SHIFT))
		goto free_vma;

	if (file) {
		int correct_wcount = 0;
		if (vma->vm_flags & VM_DENYWRITE) {
			if (file->f_dentry->d_inode->i_writecount > 0) {
				error = -ETXTBSY;
				goto free_vma;
			}
	        	/* f_op->mmap might possibly sleep
			 * (generic_file_mmap doesn't, but other code
			 * might). In any case, this takes care of any
			 * race that this might cause.
			 */
			file->f_dentry->d_inode->i_writecount--;
			correct_wcount = 1;
		}
		error = file->f_op->mmap(file, vma);
		/* Fix up the count if necessary, then check for an error */
		if (correct_wcount)
			file->f_dentry->d_inode->i_writecount++;
		if (error)
			goto unmap_and_free_vma;
		vma->vm_file = file;
		file->f_count++;
	}

	/*
	 * merge_segments may merge our vma, so we can't refer to it
	 * after the call.  Save the values we need now ...
	 */
	flags = vma->vm_flags;
	addr = vma->vm_start; /* can addr have changed?? */
	insert_vm_struct(mm, vma);
	merge_segments(mm, vma->vm_start, vma->vm_end);
	
	mm->total_vm += len >> PAGE_SHIFT;
	if (flags & VM_LOCKED) {
		mm->locked_vm += len >> PAGE_SHIFT;
		make_pages_present(addr, addr + len);
	}
	return addr;

unmap_and_free_vma:
	/* Undo any partial mapping done by a device driver. */
	flush_cache_range(mm, vma->vm_start, vma->vm_end);
	zap_page_range(mm, vma->vm_start, vma->vm_end - vma->vm_start);
	flush_tlb_range(mm, vma->vm_start, vma->vm_end);
free_vma:
	kmem_cache_free(vm_area_cachep, vma);
	return error;
}

/* Get an address range which is currently unmapped.
 * For mmap() without MAP_FIXED and shmat() with addr=0.
 * Return value 0 means ENOMEM.
 */
unsigned long get_unmapped_area(unsigned long addr, unsigned long len)
{
	struct vm_area_struct * vmm;

	if (len > TASK_SIZE)
		return 0;
	if (!addr)
		addr = TASK_UNMAPPED_BASE;
	addr = PAGE_ALIGN(addr);

	for (vmm = find_vma(current->mm, addr); ; vmm = vmm->vm_next) {
		/* At this point:  (!vmm || addr < vmm->vm_end). */
		if (TASK_SIZE - len < addr)
			return 0;
		if (!vmm || addr + len <= vmm->vm_start)
			return addr;
		addr = vmm->vm_end;
	}
}

#define vm_avl_empty	(struct vm_area_struct *) NULL

#include "mmap_avl.c"

/* Look up the first VMA which satisfies  addr < vm_end,  NULL if none. */
struct vm_area_struct * find_vma(struct mm_struct * mm, unsigned long addr)
{
	struct vm_area_struct *vma = NULL;

	if (mm) {
		/* Check the cache first. */
		/* (Cache hit rate is typically around 35%.) */
		vma = mm->mmap_cache;
		if (!(vma && vma->vm_end > addr && vma->vm_start <= addr)) {
			if (!mm->mmap_avl) {
				/* Go through the linear list. */
				vma = mm->mmap;
				while (vma && vma->vm_end <= addr)
					vma = vma->vm_next;
			} else {
				/* Then go through the AVL tree quickly. */
				struct vm_area_struct * tree = mm->mmap_avl;
				vma = NULL;
				for (;;) {
					if (tree == vm_avl_empty)
						break;
					if (tree->vm_end > addr) {
						vma = tree;
						if (tree->vm_start <= addr)
							break;
						tree = tree->vm_avl_left;
					} else
						tree = tree->vm_avl_right;
				}
			}
			if (vma)
				mm->mmap_cache = vma;
		}
	}
	return vma;
}

/* Same as find_vma, but also return a pointer to the previous VMA in *pprev. */
struct vm_area_struct * find_vma_prev(struct mm_struct * mm, unsigned long addr,
				      struct vm_area_struct **pprev)
{
	if (mm) {
		if (!mm->mmap_avl) {
			/* Go through the linear list. */
			struct vm_area_struct * prev = NULL;
			struct vm_area_struct * vma = mm->mmap;
			while (vma && vma->vm_end <= addr) {
				prev = vma;
				vma = vma->vm_next;
			}
			*pprev = prev;
			return vma;
		} else {
			/* Go through the AVL tree quickly. */
			struct vm_area_struct * vma = NULL;
			struct vm_area_struct * last_turn_right = NULL;
			struct vm_area_struct * prev = NULL;
			struct vm_area_struct * tree = mm->mmap_avl;
			for (;;) {
				if (tree == vm_avl_empty)
					break;
				if (tree->vm_end > addr) {
					vma = tree;
					prev = last_turn_right;
					if (tree->vm_start <= addr)
						break;
					tree = tree->vm_avl_left;
				} else {
					last_turn_right = tree;
					tree = tree->vm_avl_right;
				}
			}
			if (vma) {
				if (vma->vm_avl_left != vm_avl_empty) {
					prev = vma->vm_avl_left;
					while (prev->vm_avl_right != vm_avl_empty)
						prev = prev->vm_avl_right;
				}
				if ((prev ? prev->vm_next : mm->mmap) != vma)
					printk("find_vma_prev: tree inconsistent with list\n");
				*pprev = prev;
				return vma;
			}
		}
	}
	*pprev = NULL;
	return NULL;
}

/* Normal function to fix up a mapping
 * This function is the default for when an area has no specific
 * function.  This may be used as part of a more specific routine.
 * This function works out what part of an area is affected and
 * adjusts the mapping information.  Since the actual page
 * manipulation is done in do_mmap(), none need be done here,
 * though it would probably be more appropriate.
 *
 * By the time this function is called, the area struct has been
 * removed from the process mapping list, so it needs to be
 * reinserted if necessary.
 *
 * The 4 main cases are:
 *    Unmapping the whole area
 *    Unmapping from the start of the segment to a point in it
 *    Unmapping from an intermediate point to the end
 *    Unmapping between to intermediate points, making a hole.
 *
 * Case 4 involves the creation of 2 new areas, for each side of
 * the hole.  If possible, we reuse the existing area rather than
 * allocate a new one, and the return indicates whether the old
 * area was reused.
 */
static struct vm_area_struct * unmap_fixup(struct vm_area_struct *area,
	unsigned long addr, size_t len, struct vm_area_struct *extra)
{
	struct vm_area_struct *mpnt;
	unsigned long end = addr + len;

	area->vm_mm->total_vm -= len >> PAGE_SHIFT;
	if (area->vm_flags & VM_LOCKED)
		area->vm_mm->locked_vm -= len >> PAGE_SHIFT;

	/* Unmapping the whole area. */
	if (addr == area->vm_start && end == area->vm_end) {
		if (area->vm_ops && area->vm_ops->close)
			area->vm_ops->close(area);
		if (area->vm_file)
			fput(area->vm_file);
		kmem_cache_free(vm_area_cachep, area);
		return extra;
	}

	/* Work out to one of the ends. */
	if (end == area->vm_end)
		area->vm_end = addr;
	else if (addr == area->vm_start) {
		area->vm_offset += (end - area->vm_start);
		area->vm_start = end;
	} else {
	/* Unmapping a hole: area->vm_start < addr <= end < area->vm_end */
		/* Add end mapping -- leave beginning for below */
		mpnt = extra;
		extra = NULL;

		mpnt->vm_mm = area->vm_mm;
		mpnt->vm_start = end;
		mpnt->vm_end = area->vm_end;
		mpnt->vm_page_prot = area->vm_page_prot;
		mpnt->vm_flags = area->vm_flags;
		mpnt->vm_ops = area->vm_ops;
		mpnt->vm_offset = area->vm_offset + (end - area->vm_start);
		mpnt->vm_file = area->vm_file;
		mpnt->vm_pte = area->vm_pte;
		if (mpnt->vm_file)
			mpnt->vm_file->f_count++;
		if (mpnt->vm_ops && mpnt->vm_ops->open)
			mpnt->vm_ops->open(mpnt);
		area->vm_end = addr;	/* Truncate area */
		insert_vm_struct(current->mm, mpnt);
	}

	insert_vm_struct(current->mm, area);
	return extra;
}

/*
 * Try to free as many page directory entries as we can,
 * without having to work very hard at actually scanning
 * the page tables themselves.
 *
 * Right now we try to free page tables if we have a nice
 * PGDIR-aligned area that got free'd up. We could be more
 * granular if we want to, but this is fast and simple,
 * and covers the bad cases.
 *
 * "prev", if it exists, points to a vma before the one
 * we just free'd - but there's no telling how much before.
 */
static void free_pgtables(struct mm_struct * mm, struct vm_area_struct *prev,
	unsigned long start, unsigned long end)
{
	unsigned long first = start & PGDIR_MASK;
	unsigned long last = (end + PGDIR_SIZE - 1) & PGDIR_MASK;

	if (!prev) {
		prev = mm->mmap;
		if (!prev)
			goto no_mmaps;
		if (prev->vm_end > start) {
			if (last > prev->vm_start)
				last = prev->vm_start;
			goto no_mmaps;
		}
	}
	for (;;) {
		struct vm_area_struct *next = prev->vm_next;

		if (next) {
			if (next->vm_start < start) {
				prev = next;
				continue;
			}
			if (last > next->vm_start)
				last = next->vm_start;
		}
		if (prev->vm_end > first)
			first = prev->vm_end + PGDIR_SIZE - 1;
		break;
	}
no_mmaps:
	first = first >> PGDIR_SHIFT;
	last = last >> PGDIR_SHIFT;
	if (last > first)
		clear_page_tables(mm, first, last-first);
}

/* Munmap is split into 2 main parts -- this part which finds
 * what needs doing, and the areas themselves, which do the
 * work.  This now handles partial unmappings.
 * Jeremy Fitzhardine <jeremy@sw.oz.au>
 */
int do_munmap(unsigned long addr, size_t len)
{
	struct mm_struct * mm;
	struct vm_area_struct *mpnt, *prev, **npp, *free, *extra;

	if ((addr & ~PAGE_MASK) || addr > TASK_SIZE || len > TASK_SIZE-addr)
		return -EINVAL;

	if ((len = PAGE_ALIGN(len)) == 0)
		return -EINVAL;

	/* Check if this memory area is ok - put it on the temporary
	 * list if so..  The checks here are pretty simple --
	 * every area affected in some way (by any overlap) is put
	 * on the list.  If nothing is put on, nothing is affected.
	 */
	mm = current->mm;
	mpnt = find_vma_prev(mm, addr, &prev);
	if (!mpnt)
		return 0;
	/* we have  addr < mpnt->vm_end  */

	if (mpnt->vm_start >= addr+len)
		return 0;

	/* If we'll make "hole", check the vm areas limit */
	if ((mpnt->vm_start < addr && mpnt->vm_end > addr+len)
	    && mm->map_count >= MAX_MAP_COUNT)
		return -ENOMEM;

	/*
	 * We may need one additional vma to fix up the mappings ... 
	 * and this is the last chance for an easy error exit.
	 */
	extra = kmem_cache_alloc(vm_area_cachep, SLAB_KERNEL);
	if (!extra)
		return -ENOMEM;

	npp = (prev ? &prev->vm_next : &mm->mmap);
	free = NULL;
	for ( ; mpnt && mpnt->vm_start < addr+len; mpnt = *npp) {
		*npp = mpnt->vm_next;
		mpnt->vm_next = free;
		free = mpnt;
		if (mm->mmap_avl)
			avl_remove(mpnt, &mm->mmap_avl);
	}

	/* Ok - we have the memory areas we should free on the 'free' list,
	 * so release them, and unmap the page range..
	 * If the one of the segments is only being partially unmapped,
	 * it will put new vm_area_struct(s) into the address space.
	 */
	while ((mpnt = free) != NULL) {
		unsigned long st, end, size;

		free = free->vm_next;

		st = addr < mpnt->vm_start ? mpnt->vm_start : addr;
		end = addr+len;
		end = end > mpnt->vm_end ? mpnt->vm_end : end;
		size = end - st;

		if (mpnt->vm_ops && mpnt->vm_ops->unmap)
			mpnt->vm_ops->unmap(mpnt, st, size);

		remove_shared_vm_struct(mpnt);
		mm->map_count--;

		flush_cache_range(mm, st, end);
		zap_page_range(mm, st, size);
		flush_tlb_range(mm, st, end);

		/*
		 * Fix the mapping, and free the old area if it wasn't reused.
		 */
		extra = unmap_fixup(mpnt, st, size, extra);
	}

	/* Release the extra vma struct if it wasn't used */
	if (extra)
		kmem_cache_free(vm_area_cachep, extra);

	free_pgtables(mm, prev, addr, addr+len);

	mm->mmap_cache = NULL;	/* Kill the cache. */
	return 0;
}

asmlinkage int sys_munmap(unsigned long addr, size_t len)
{
	int ret;

	down(&current->mm->mmap_sem);
	lock_kernel();
	ret = do_munmap(addr, len);
	unlock_kernel();
	up(&current->mm->mmap_sem);
	return ret;
}

/* Build the AVL tree corresponding to the VMA list. */
void build_mmap_avl(struct mm_struct * mm)
{
	struct vm_area_struct * vma;

	mm->mmap_avl = NULL;
	for (vma = mm->mmap; vma; vma = vma->vm_next)
		avl_insert(vma, &mm->mmap_avl);
}

/* Release all mmaps. */
void exit_mmap(struct mm_struct * mm)
{
	struct vm_area_struct * mpnt;

	mpnt = mm->mmap;
	mm->mmap = mm->mmap_avl = mm->mmap_cache = NULL;
	mm->rss = 0;
	mm->total_vm = 0;
	mm->locked_vm = 0;
	while (mpnt) {
		struct vm_area_struct * next = mpnt->vm_next;
		unsigned long start = mpnt->vm_start;
		unsigned long end = mpnt->vm_end;
		unsigned long size = end - start;

		if (mpnt->vm_ops) {
			if (mpnt->vm_ops->unmap)
				mpnt->vm_ops->unmap(mpnt, start, size);
			if (mpnt->vm_ops->close)
				mpnt->vm_ops->close(mpnt);
		}
		mm->map_count--;
		remove_shared_vm_struct(mpnt);
		zap_page_range(mm, start, size);
		if (mpnt->vm_file)
			fput(mpnt->vm_file);
		kmem_cache_free(vm_area_cachep, mpnt);
		mpnt = next;
	}

	/* This is just debugging */
	if (mm->map_count)
		printk("exit_mmap: map count is %d\n", mm->map_count);

	clear_page_tables(mm, 0, USER_PTRS_PER_PGD);
}

/* Insert vm structure into process list sorted by address
 * and into the inode's i_mmap ring.
 */
void insert_vm_struct(struct mm_struct *mm, struct vm_area_struct *vmp)
{
	struct vm_area_struct **pprev;
	struct file * file;

	if (!mm->mmap_avl) {
		pprev = &mm->mmap;
		while (*pprev && (*pprev)->vm_start <= vmp->vm_start)
			pprev = &(*pprev)->vm_next;
	} else {
		struct vm_area_struct *prev, *next;
		avl_insert_neighbours(vmp, &mm->mmap_avl, &prev, &next);
		pprev = (prev ? &prev->vm_next : &mm->mmap);
		if (*pprev != next)
			printk("insert_vm_struct: tree inconsistent with list\n");
	}
	vmp->vm_next = *pprev;
	*pprev = vmp;

	mm->map_count++;
	if (mm->map_count >= AVL_MIN_MAP_COUNT && !mm->mmap_avl)
		build_mmap_avl(mm);

	file = vmp->vm_file;
	if (file) {
		struct inode * inode = file->f_dentry->d_inode;
		if (vmp->vm_flags & VM_DENYWRITE)
			inode->i_writecount--;
      
		/* insert vmp into inode's share list */
		if((vmp->vm_next_share = inode->i_mmap) != NULL)
			inode->i_mmap->vm_pprev_share = &vmp->vm_next_share;
		inode->i_mmap = vmp;
		vmp->vm_pprev_share = &inode->i_mmap;
	}
}

/* Merge the list of memory segments if possible.
 * Redundant vm_area_structs are freed.
 * This assumes that the list is ordered by address.
 * We don't need to traverse the entire list, only those segments
 * which intersect or are adjacent to a given interval.
 *
 * We must already hold the mm semaphore when we get here..
 */
void merge_segments (struct mm_struct * mm, unsigned long start_addr, unsigned long end_addr)
{
	struct vm_area_struct *prev, *mpnt, *next, *prev1;

	mpnt = find_vma_prev(mm, start_addr, &prev1);
	if (!mpnt)
		return;

	if (prev1) {
		prev = prev1;
	} else {
		prev = mpnt;
		mpnt = mpnt->vm_next;
	}

	/* prev and mpnt cycle through the list, as long as
	 * start_addr < mpnt->vm_end && prev->vm_start < end_addr
	 */
	for ( ; mpnt && prev->vm_start < end_addr ; prev = mpnt, mpnt = next) {
		next = mpnt->vm_next;

		/* To share, we must have the same file, operations.. */
		if ((mpnt->vm_file != prev->vm_file)||
		    (mpnt->vm_pte != prev->vm_pte)	||
		    (mpnt->vm_ops != prev->vm_ops)	||
		    (mpnt->vm_flags != prev->vm_flags)	||
		    (prev->vm_end != mpnt->vm_start))
			continue;

		/*
		 * If we have a file or it's a shared memory area
		 * the offsets must be contiguous..
		 */
		if ((mpnt->vm_file != NULL) || (mpnt->vm_flags & VM_SHM)) {
			unsigned long off = prev->vm_offset+prev->vm_end-prev->vm_start;
			if (off != mpnt->vm_offset)
				continue;
		}

		/* merge prev with mpnt and set up pointers so the new
		 * big segment can possibly merge with the next one.
		 * The old unused mpnt is freed.
		 */
		if (mm->mmap_avl)
			avl_remove(mpnt, &mm->mmap_avl);
		prev->vm_end = mpnt->vm_end;
		prev->vm_next = mpnt->vm_next;
		if (mpnt->vm_ops && mpnt->vm_ops->close) {
			mpnt->vm_offset += mpnt->vm_end - mpnt->vm_start;
			mpnt->vm_start = mpnt->vm_end;
			mpnt->vm_ops->close(mpnt);
		}
		mm->map_count--;
		remove_shared_vm_struct(mpnt);
		if (mpnt->vm_file)
			fput(mpnt->vm_file);
		kmem_cache_free(vm_area_cachep, mpnt);
		mpnt = prev;
	}
	mm->mmap_cache = NULL;		/* Kill the cache. */
}

void __init vma_init(void)
{
	vm_area_cachep = kmem_cache_create("vm_area_struct",
					   sizeof(struct vm_area_struct),
					   0, SLAB_HWCACHE_ALIGN,
					   NULL, NULL);
	if(!vm_area_cachep)
		panic("vma_init: Cannot alloc vm_area_struct cache.");

	mm_cachep = kmem_cache_create("mm_struct",
				      sizeof(struct mm_struct),
				      0, SLAB_HWCACHE_ALIGN,
				      NULL, NULL);
	if(!mm_cachep)
		panic("vma_init: Cannot alloc mm_struct cache.");
}