summaryrefslogtreecommitdiffstats
path: root/src/H5Ocache.c
blob: 3ccdf1182123dc6196dcc34af07de7d1aa5b207b (plain)
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
879
880
881
882
883
884
885
886
887
888
889
890
891
892
893
894
895
896
897
898
899
900
901
902
903
904
905
906
907
908
909
910
911
912
913
914
915
916
917
918
919
920
921
922
923
924
925
926
927
928
929
930
931
932
933
934
935
936
937
938
939
940
941
942
943
944
945
946
947
948
949
950
951
952
953
954
955
956
957
958
959
960
961
962
963
964
965
966
967
968
969
970
971
972
973
974
975
976
977
978
979
980
981
982
983
984
985
986
987
988
989
990
991
992
993
994
995
996
997
998
999
1000
1001
1002
1003
1004
1005
1006
1007
1008
1009
1010
1011
1012
1013
1014
1015
1016
1017
1018
1019
1020
1021
1022
1023
1024
1025
1026
1027
1028
1029
1030
1031
1032
1033
1034
1035
1036
1037
1038
1039
1040
1041
1042
1043
1044
1045
1046
1047
1048
1049
1050
1051
1052
1053
1054
1055
1056
1057
1058
1059
1060
1061
1062
1063
1064
1065
1066
1067
1068
1069
1070
1071
1072
1073
1074
1075
1076
1077
1078
1079
1080
1081
1082
1083
1084
1085
1086
1087
1088
1089
1090
1091
1092
1093
1094
1095
1096
1097
1098
1099
1100
1101
1102
1103
1104
1105
1106
1107
1108
1109
1110
1111
1112
1113
1114
1115
1116
1117
1118
1119
1120
1121
1122
1123
1124
1125
1126
1127
1128
1129
1130
1131
1132
1133
1134
1135
1136
1137
1138
1139
1140
1141
1142
1143
1144
1145
1146
1147
1148
1149
1150
1151
1152
1153
1154
1155
1156
1157
1158
1159
1160
1161
1162
1163
1164
1165
1166
1167
1168
1169
1170
1171
1172
1173
1174
1175
1176
1177
1178
1179
1180
1181
1182
1183
1184
1185
1186
1187
1188
1189
1190
1191
1192
1193
1194
1195
1196
1197
1198
1199
1200
1201
1202
1203
1204
1205
1206
1207
1208
1209
1210
1211
1212
1213
1214
1215
1216
1217
1218
1219
1220
1221
1222
1223
1224
1225
1226
1227
1228
1229
1230
1231
1232
1233
1234
1235
1236
1237
1238
1239
1240
1241
1242
1243
1244
1245
1246
1247
1248
1249
1250
1251
1252
1253
1254
1255
1256
1257
1258
1259
1260
1261
1262
1263
1264
1265
1266
1267
1268
1269
1270
1271
1272
1273
1274
1275
1276
1277
1278
1279
1280
1281
1282
1283
1284
1285
1286
1287
1288
1289
1290
1291
1292
1293
1294
1295
1296
1297
1298
1299
1300
1301
1302
1303
1304
1305
1306
1307
1308
1309
1310
1311
1312
1313
1314
1315
1316
1317
1318
1319
1320
1321
1322
1323
1324
1325
1326
1327
1328
1329
1330
1331
1332
1333
1334
1335
1336
1337
1338
1339
1340
1341
1342
1343
1344
1345
1346
1347
1348
1349
1350
1351
1352
1353
1354
1355
1356
1357
1358
1359
1360
1361
1362
1363
1364
1365
1366
1367
1368
1369
1370
1371
1372
1373
1374
1375
1376
1377
1378
1379
1380
1381
1382
1383
1384
1385
1386
1387
1388
1389
1390
1391
1392
1393
1394
1395
1396
1397
1398
1399
1400
1401
1402
1403
1404
1405
1406
1407
1408
1409
1410
1411
1412
1413
1414
1415
1416
1417
1418
1419
1420
1421
1422
1423
1424
1425
1426
1427
1428
1429
1430
1431
1432
1433
1434
1435
1436
1437
1438
1439
1440
1441
1442
1443
1444
1445
1446
1447
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
 * Copyright by The HDF Group.                                               *
 * Copyright by the Board of Trustees of the University of Illinois.         *
 * All rights reserved.                                                      *
 *                                                                           *
 * This file is part of HDF5.  The full HDF5 copyright notice, including     *
 * terms governing use, modification, and redistribution, is contained in    *
 * the files COPYING and Copyright.html.  COPYING can be found at the root   *
 * of the source code distribution tree; Copyright.html can be found at the  *
 * root level of an installed copy of the electronic HDF5 document set and   *
 * is linked from the top-level documents page.  It can also be found at     *
 * http://hdfgroup.org/HDF5/doc/Copyright.html.  If you do not have          *
 * access to either file, you may request a copy from help@hdfgroup.org.     *
 * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */

/*-------------------------------------------------------------------------
 *
 * Created:		H5Ocache.c
 *			Sep 28 2005
 *			Quincey Koziol <koziol@ncsa.uiuc.edu>
 *
 * Purpose:		Object header metadata cache virtual functions.
 *
 *-------------------------------------------------------------------------
 */

/****************/
/* Module Setup */
/****************/

#define H5O_PACKAGE		/*suppress error about including H5Opkg	  */


/***********/
/* Headers */
/***********/
#include "H5private.h"		/* Generic Functions			*/
#include "H5Eprivate.h"		/* Error handling		  	*/
#include "H5FLprivate.h"	/* Free lists                           */
#include "H5MFprivate.h"	/* File memory management		*/
#include "H5Opkg.h"             /* Object headers			*/
#include "H5WBprivate.h"        /* Wrapped Buffers                      */


/****************/
/* Local Macros */
/****************/

/* Set the object header size to speculatively read in */
/* (needs to be more than the object header prefix size to work at all and
 *      should be larger than the largest object type's default object header
 *      size to save the extra I/O operations) */
#define H5O_SPEC_READ_SIZE 512


/******************/
/* Local Typedefs */
/******************/


/********************/
/* Package Typedefs */
/********************/


/********************/
/* Local Prototypes */
/********************/

/* Metadata cache callbacks */
static H5O_t *H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, void *udata);
static herr_t H5O_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5O_t *oh, unsigned UNUSED * flags_ptr);
static herr_t H5O_dest(H5F_t *f, H5O_t *oh);
static herr_t H5O_clear(H5F_t *f, H5O_t *oh, hbool_t destroy);
static herr_t H5O_size(const H5F_t *f, const H5O_t *oh, size_t *size_ptr);

static H5O_chunk_proxy_t *H5O_cache_chk_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, void *udata);
static herr_t H5O_cache_chk_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr, H5O_chunk_proxy_t *chk_proxy, unsigned UNUSED * flags_ptr);
static herr_t H5O_cache_chk_dest(H5F_t *f, H5O_chunk_proxy_t *chk_proxy);
static herr_t H5O_cache_chk_clear(H5F_t *f, H5O_chunk_proxy_t *chk_proxy, hbool_t destroy);
static herr_t H5O_cache_chk_size(const H5F_t *f, const H5O_chunk_proxy_t *chk_proxy, size_t *size_ptr);

/* Chunk proxy routines */
static herr_t H5O__chunk_proxy_dest(H5O_chunk_proxy_t *chunk_proxy);

/* Chunk routines */
static herr_t H5O__chunk_deserialize(H5O_t *oh, haddr_t addr, size_t len,
    const uint8_t *image, H5O_common_cache_ud_t *udata, hbool_t *dirty);
static herr_t H5O__chunk_serialize(const H5F_t *f, H5O_t *oh, unsigned chunkno);

/* Misc. routines */
static herr_t H5O__add_cont_msg(H5O_cont_msgs_t *cont_msg_info,
    const H5O_cont_t *cont);


/*********************/
/* Package Variables */
/*********************/

/* H5O object header prefix inherits cache-like properties from H5AC */
const H5AC_class_t H5AC_OHDR[1] = {{
    H5AC_OHDR_ID,
    (H5AC_load_func_t)H5O_load,
    (H5AC_flush_func_t)H5O_flush,
    (H5AC_dest_func_t)H5O_dest,
    (H5AC_clear_func_t)H5O_clear,
    (H5AC_notify_func_t)NULL,
    (H5AC_size_func_t)H5O_size,
}};

/* H5O object header chunk inherits cache-like properties from H5AC */
const H5AC_class_t H5AC_OHDR_CHK[1] = {{
    H5AC_OHDR_CHK_ID,
    (H5AC_load_func_t)H5O_cache_chk_load,
    (H5AC_flush_func_t)H5O_cache_chk_flush,
    (H5AC_dest_func_t)H5O_cache_chk_dest,
    (H5AC_clear_func_t)H5O_cache_chk_clear,
    (H5AC_notify_func_t)NULL,
    (H5AC_size_func_t)H5O_cache_chk_size,
}};

/* Declare external the free list for H5O_unknown_t's */
H5FL_EXTERN(H5O_unknown_t);

/* Declare extern the free list for H5O_chunk_proxy_t's */
H5FL_EXTERN(H5O_chunk_proxy_t);

/* Declare the free list for H5O_cont_t sequences */
H5FL_SEQ_DEFINE(H5O_cont_t);


/*****************************/
/* Library Private Variables */
/*****************************/


/*******************/
/* Local Variables */
/*******************/



/*-------------------------------------------------------------------------
 * Function:	H5O_load
 *
 * Purpose:	Loads an object header from disk.
 *
 * Return:	Success:	Pointer to the new object header.
 *
 *		Failure:	NULL
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  5 1997
 *
 *-------------------------------------------------------------------------
 */
static H5O_t *
H5O_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, void *_udata)
{
    H5O_t	*oh = NULL;     /* Object header read in */
    H5O_cache_ud_t *udata = (H5O_cache_ud_t *)_udata;       /* User data for callback */
    H5WB_t      *wb = NULL;     /* Wrapped buffer for prefix data */
    uint8_t     read_buf[H5O_SPEC_READ_SIZE];       /* Buffer for speculative read */
    const uint8_t *p;           /* Pointer into buffer to decode */
    uint8_t     *buf;           /* Buffer to decode */
    size_t	spec_read_size; /* Size of buffer to speculatively read in */
    size_t	prefix_size;    /* Size of object header prefix */
    size_t	buf_size;       /* Size of prefix+chunk #0 buffer */
    haddr_t     eoa;		/* Relative end of file address	*/
    H5O_t	*ret_value;     /* Return value */

    FUNC_ENTER_NOAPI_NOINIT

    /* Check arguments */
    HDassert(f);
    HDassert(H5F_addr_defined(addr));
    HDassert(udata);
    HDassert(udata->common.f);
    HDassert(udata->common.cont_msg_info);

    /* Make certain we don't speculatively read off the end of the file */
    if(HADDR_UNDEF == (eoa = H5F_get_eoa(f, H5FD_MEM_OHDR)))
        HGOTO_ERROR(H5E_OHDR, H5E_CANTGET, NULL, "unable to determine file size")

    /* Compute the size of the speculative object header buffer */
    H5_CHECKED_ASSIGN(spec_read_size, size_t, MIN(eoa - addr, H5O_SPEC_READ_SIZE), hsize_t);

    /* Attempt to speculatively read both object header prefix and first chunk */
    if(H5F_block_read(f, H5FD_MEM_OHDR, addr, spec_read_size, dxpl_id, read_buf) < 0)
	HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL, "unable to read object header")
    p = read_buf;

    /* Allocate space for the object header data structure */
    if(NULL == (oh = H5FL_CALLOC(H5O_t)))
        HGOTO_ERROR(H5E_RESOURCE, H5E_NOSPACE, NULL, "memory allocation failed")

    /* File-specific, non-stored information */
    oh->sizeof_size = H5F_SIZEOF_SIZE(udata->common.f);
    oh->sizeof_addr = H5F_SIZEOF_ADDR(udata->common.f);

    /* Check for presence of magic number */
    /* (indicates version 2 or later) */
    if(!HDmemcmp(p, H5O_HDR_MAGIC, (size_t)H5_SIZEOF_MAGIC)) {
        /* Magic number */
        p += H5_SIZEOF_MAGIC;

        /* Version */
        oh->version = *p++;
        if(H5O_VERSION_2 != oh->version)
            HGOTO_ERROR(H5E_OHDR, H5E_VERSION, NULL, "bad object header version number")

        /* Flags */
        oh->flags = *p++;
        if(oh->flags & ~H5O_HDR_ALL_FLAGS)
            HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "unknown object header status flag(s)")

        /* Number of links to object (unless overridden by refcount message) */
        oh->nlink = 1;

        /* Time fields */
        if(oh->flags & H5O_HDR_STORE_TIMES) {
            uint32_t tmp;       /* Temporary value */

            UINT32DECODE(p, tmp);
            oh->atime = (time_t)tmp;
            UINT32DECODE(p, tmp);
            oh->mtime = (time_t)tmp;
            UINT32DECODE(p, tmp);
            oh->ctime = (time_t)tmp;
            UINT32DECODE(p, tmp);
            oh->btime = (time_t)tmp;
        } /* end if */
        else
            oh->atime = oh->mtime = oh->ctime = oh->btime = 0;

        /* Attribute fields */
        if(oh->flags & H5O_HDR_ATTR_STORE_PHASE_CHANGE) {
            UINT16DECODE(p, oh->max_compact);
            UINT16DECODE(p, oh->min_dense);
            if(oh->max_compact < oh->min_dense)
                HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "bad object header attribute phase change values")
        } /* end if */
        else {
            oh->max_compact = H5O_CRT_ATTR_MAX_COMPACT_DEF;
            oh->min_dense = H5O_CRT_ATTR_MIN_DENSE_DEF;
        } /* end else */

        /* First chunk size */
        switch(oh->flags & H5O_HDR_CHUNK0_SIZE) {
            case 0:     /* 1 byte size */
                oh->chunk0_size = *p++;
                break;

            case 1:     /* 2 byte size */
                UINT16DECODE(p, oh->chunk0_size);
                break;

            case 2:     /* 4 byte size */
                UINT32DECODE(p, oh->chunk0_size);
                break;

            case 3:     /* 8 byte size */
                UINT64DECODE(p, oh->chunk0_size);
                break;

            default:
                HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "bad size for chunk 0")
        } /* end switch */
        if(oh->chunk0_size > 0 && oh->chunk0_size < H5O_SIZEOF_MSGHDR_OH(oh))
            HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "bad object header chunk size")
    } /* end if */
    else {
        /* Version */
        oh->version = *p++;
        if(H5O_VERSION_1 != oh->version)
            HGOTO_ERROR(H5E_OHDR, H5E_VERSION, NULL, "bad object header version number")

        /* Flags */
        oh->flags = H5O_CRT_OHDR_FLAGS_DEF;

        /* Reserved */
        p++;

        /* Number of messages */
        UINT16DECODE(p, udata->v1_pfx_nmesgs);

        /* Link count */
        UINT32DECODE(p, oh->nlink);

        /* Reset unused time fields */
        oh->atime = oh->mtime = oh->ctime = oh->btime = 0;

        /* Reset unused attribute fields */
        oh->max_compact = 0;
        oh->min_dense = 0;

        /* First chunk size */
        UINT32DECODE(p, oh->chunk0_size);
        if((udata->v1_pfx_nmesgs > 0 && oh->chunk0_size < H5O_SIZEOF_MSGHDR_OH(oh)) ||
                (udata->v1_pfx_nmesgs == 0 && oh->chunk0_size > 0))
            HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, NULL, "bad object header chunk size")

        /* Reserved, in version 1 (for 8-byte alignment padding) */
        p += 4;
    } /* end else */

    /* Determine object header prefix length */
    prefix_size = (size_t)(p - (const uint8_t *)read_buf);
    HDassert((size_t)prefix_size == (size_t)(H5O_SIZEOF_HDR(oh) - H5O_SIZEOF_CHKSUM_OH(oh)));

    /* Compute the size of the buffer used */
    buf_size = oh->chunk0_size + (size_t)H5O_SIZEOF_HDR(oh);

    /* Check if the speculative read was large enough to parse the first chunk */
    if(spec_read_size < buf_size) {
        /* Wrap the local buffer for serialized header info */
        if(NULL == (wb = H5WB_wrap(read_buf, sizeof(read_buf))))
            HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "can't wrap buffer")

        /* Get a pointer to a buffer that's large enough for serialized header */
        if(NULL == (buf = (uint8_t *)H5WB_actual(wb, buf_size)))
            HGOTO_ERROR(H5E_OHDR, H5E_NOSPACE, NULL, "can't get actual buffer")

        /* Copy existing raw data into new buffer */
        HDmemcpy(buf, read_buf, spec_read_size);

        /* Read rest of the raw data */
        if(H5F_block_read(f, H5FD_MEM_OHDR, (addr + spec_read_size), (buf_size - spec_read_size), dxpl_id, (buf + spec_read_size)) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL, "unable to read object header data")
    } /* end if */
    else
        buf = read_buf;

    /* Parse the first chunk */
    if(H5O__chunk_deserialize(oh, udata->common.addr, oh->chunk0_size, buf, &(udata->common), &oh->cache_info.is_dirty) < 0)
        HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "can't deserialize first object header chunk")

    /* Note that we've loaded the object header from the file */
    udata->made_attempt = TRUE;

    /* Set return value */
    ret_value = oh;

done:
    /* Release resources */
    if(wb && H5WB_unwrap(wb) < 0)
        HDONE_ERROR(H5E_OHDR, H5E_CLOSEERROR, NULL, "can't close wrapped buffer")

    /* Release the [possibly partially initialized] object header on errors */
    if(!ret_value && oh)
        if(H5O_free(oh) < 0)
            HDONE_ERROR(H5E_OHDR, H5E_CANTRELEASE, NULL, "unable to destroy object header data")

    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5O_load() */


/*-------------------------------------------------------------------------
 * Function:	H5O_flush
 *
 * Purpose:	Flushes (and destroys) an object header.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	Robb Matzke
 *		matzke@llnl.gov
 *		Aug  5 1997
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t UNUSED addr, H5O_t *oh, unsigned UNUSED * flags_ptr)
{
    herr_t ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_NOAPI_NOINIT

    /* Check arguments */
    HDassert(f);
    HDassert(H5F_addr_defined(addr));
    HDassert(oh);

    /* flush */
    if(oh->cache_info.is_dirty) {
        uint8_t	*p;             /* Pointer to object header prefix buffer */

#ifdef H5O_DEBUG
H5O_assert(oh);
#endif /* H5O_DEBUG */

        /* Point to raw data 'image' for first chunk, which has room for the prefix */
        p = oh->chunk[0].image;

        /* Later versions of object header prefix have different format and
         * also require that chunk 0 always be updated, since the checksum
         * on the entire block of memory needs to be updated if anything is
         * modified */
        if(oh->version > H5O_VERSION_1) {
            uint64_t chunk0_size;       /* Size of chunk 0's data */

            HDassert(oh->chunk[0].size >= (size_t)H5O_SIZEOF_HDR(oh));
            chunk0_size = oh->chunk[0].size - (size_t)H5O_SIZEOF_HDR(oh);

            /* Verify magic number */
            HDassert(!HDmemcmp(p, H5O_HDR_MAGIC, H5_SIZEOF_MAGIC));
            p += H5_SIZEOF_MAGIC;

            /* Version */
            *p++ = oh->version;

            /* Flags */
            *p++ = oh->flags;

            /* Time fields */
            if(oh->flags & H5O_HDR_STORE_TIMES) {
                UINT32ENCODE(p, oh->atime);
                UINT32ENCODE(p, oh->mtime);
                UINT32ENCODE(p, oh->ctime);
                UINT32ENCODE(p, oh->btime);
            } /* end if */

            /* Attribute fields */
            if(oh->flags & H5O_HDR_ATTR_STORE_PHASE_CHANGE) {
                UINT16ENCODE(p, oh->max_compact);
                UINT16ENCODE(p, oh->min_dense);
            } /* end if */

            /* First chunk size */
            switch(oh->flags & H5O_HDR_CHUNK0_SIZE) {
                case 0:     /* 1 byte size */
                    HDassert(chunk0_size < 256);
                    *p++ = (uint8_t)chunk0_size;
                    break;

                case 1:     /* 2 byte size */
                    HDassert(chunk0_size < 65536);
                    UINT16ENCODE(p, chunk0_size);
                    break;

                case 2:     /* 4 byte size */
		    /* use <= 2**32 -1 to stay within 4 bytes integer range */
                    HDassert(chunk0_size <= 4294967295UL);
                    UINT32ENCODE(p, chunk0_size);
                    break;

                case 3:     /* 8 byte size */
                    UINT64ENCODE(p, chunk0_size);
                    break;

                default:
                    HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, FAIL, "bad size for chunk 0")
            } /* end switch */
        } /* end if */
        else {
            /* Version */
            *p++ = oh->version;

            /* Reserved */
            *p++ = 0;

            /* Number of messages */
#ifdef H5O_ENABLE_BAD_MESG_COUNT
            if(oh->store_bad_mesg_count)
                UINT16ENCODE(p, (oh->nmesgs - 1))
            else
#endif /* H5O_ENABLE_BAD_MESG_COUNT */
                UINT16ENCODE(p, oh->nmesgs);

            /* Link count */
            UINT32ENCODE(p, oh->nlink);

            /* First chunk size */
            UINT32ENCODE(p, (oh->chunk[0].size - (size_t)H5O_SIZEOF_HDR(oh)));

            /* Zero to alignment */
            HDmemset(p, 0, (size_t)(H5O_SIZEOF_HDR(oh) - 12));
            p += (size_t)(H5O_SIZEOF_HDR(oh) - 12);
        } /* end else */
        HDassert((size_t)(p - oh->chunk[0].image) == (size_t)(H5O_SIZEOF_HDR(oh) - H5O_SIZEOF_CHKSUM_OH(oh)));

        /* Serialize messages for this chunk */
        if(H5O__chunk_serialize(f, oh, (unsigned)0) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTSERIALIZE, FAIL, "unable to serialize first object header chunk")

        /* Write the chunk out */
        HDassert(H5F_addr_defined(oh->chunk[0].addr));
        if(H5F_block_write(f, H5FD_MEM_OHDR, oh->chunk[0].addr, oh->chunk[0].size, dxpl_id, oh->chunk[0].image) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to write object header chunk to disk")

        /* Mark object header as clean now */
	oh->cache_info.is_dirty = FALSE;
    } /* end if */

    /* Destroy the object header, if requested */
    if(destroy)
        if(H5O_dest(f, oh) < 0)
	    HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to destroy object header data")

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5O_flush() */


/*-------------------------------------------------------------------------
 * Function:	H5O_dest
 *
 * Purpose:	Destroys an object header.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	Quincey Koziol
 *		koziol@ncsa.uiuc.edu
 *		Jan 15 2003
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_dest(H5F_t *f, H5O_t *oh)
{
    herr_t ret_value = SUCCEED;         /* Return value */

    FUNC_ENTER_NOAPI_NOINIT

    /* Check arguments */
    HDassert(oh);
    HDassert(oh->rc == 0);

    /* Verify that node is clean */
    HDassert(!oh->cache_info.is_dirty);

    /* If we're going to free the space on disk, the address must be valid */
    HDassert(!oh->cache_info.free_file_space_on_destroy || H5F_addr_defined(oh->cache_info.addr));

    /* Check for releasing file space for object header */
    if(oh->chunk && oh->cache_info.free_file_space_on_destroy) {
        /* Free main (first) object header "chunk" */
        /* (XXX: Nasty usage of internal DXPL value! -QAK) */
        if(H5MF_xfree(f, H5FD_MEM_OHDR, H5AC_dxpl_id, oh->chunk[0].addr, (hsize_t)oh->chunk[0].size) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to free object header")
    } /* end if */

    /* Destroy object header */
    if(H5O_free(oh) < 0)
        HGOTO_ERROR(H5E_OHDR, H5E_CANTRELEASE, FAIL, "can't destroy object header")

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5O_dest() */


/*-------------------------------------------------------------------------
 * Function:	H5O_clear
 *
 * Purpose:	Mark a object header in memory as non-dirty.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	Quincey Koziol
 *		koziol@ncsa.uiuc.edu
 *		Mar 20 2003
 *
 * Changes:     In the parallel case, there is the possibility that the
 *              the object header may be flushed by different processes
 *              over the life of the computation.  Thus we must ensure
 *              that the chunk images are up to date before we mark the
 *              messages clean -- as otherwise we may overwrite valid
 *              data with a blank section of a chunk image.
 *
 *              To deal with this, I have added code to call
 *              H5O_chunk_serialize() for all chunks before we
 *              mark all messages as clean if we are not destroying the
 *              object.  Do this in the parallel case only, as the problem
 *              can only occur in this context.
 *
 *                                              JRM -- 10/12/10
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_clear(H5F_t *f, H5O_t *oh, hbool_t destroy)
{
    unsigned	u;      /* Local index variable */
    herr_t ret_value = SUCCEED;

    FUNC_ENTER_NOAPI_NOINIT

    /* Check arguments */
    HDassert(oh);

#ifdef H5_HAVE_PARALLEL
    if ( ( oh->cache_info.is_dirty ) && ( ! destroy ) ) {

        size_t i;

        /* scan through all chunks associated with the object header,
         * and cause them to update their images for all entries currently
         * marked dirty.  Must do this in the parallel case, as it is possible
         * that this processor may clear this object header several times
         * before flushing it -- thus causing undefined sections of the image
         * to be written to disk overwriting valid data.
         */

        for ( i = 0; i < oh->nchunks; i++ ) {

            if(H5O__chunk_serialize(f, oh, i) < 0)
                HGOTO_ERROR(H5E_OHDR, H5E_CANTSERIALIZE, FAIL, "unable to serialize object header chunk")
        }
    }
#endif /* H5_HAVE_PARALLEL */

    /* Mark messages stored with the object header (i.e. messages in chunk 0) as clean */
    for(u = 0; u < oh->nmesgs; u++)
        oh->mesg[u].dirty = FALSE;

#ifndef NDEBUG
    /* Reset the number of messages dirtied by decoding */
    oh->ndecode_dirtied = 0;
#endif /* NDEBUG */

    /* Mark whole header as clean */
    oh->cache_info.is_dirty = FALSE;

    if(destroy)
        if(H5O_dest(f, oh) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to destroy object header data")

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5O_clear() */


/*-------------------------------------------------------------------------
 * Function:	H5O_size
 *
 * Purpose:	Compute the size in bytes of the specified instance of
 *              H5O_t on disk, and return it in *len_ptr.  On failure,
 *              the value of *len_ptr is undefined.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	John Mainzer
 *		5/13/04
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_size(const H5F_t UNUSED *f, const H5O_t *oh, size_t *size_ptr)
{
    FUNC_ENTER_NOAPI_NOINIT_NOERR

    /* check args */
    HDassert(oh);
    HDassert(size_ptr);

    /* Report the object header's prefix+first chunk length */
    if(oh->chunk0_size)
       *size_ptr = (size_t)H5O_SIZEOF_HDR(oh) + oh->chunk0_size;
    else
       *size_ptr = oh->chunk[0].size;

    FUNC_LEAVE_NOAPI(SUCCEED)
} /* H5O_size() */


/*-------------------------------------------------------------------------
 * Function:	H5O_cache_chk_load
 *
 * Purpose:	Loads an object header continuation chunk from disk.
 *
 * Return:	Success:	Pointer to the new object header chunk proxy.
 *		Failure:	NULL
 *
 * Programmer:	Quincey Koziol
 *		koziol@hdfgroup.org
 *		Jul 12 2008
 *
 *-------------------------------------------------------------------------
 */
static H5O_chunk_proxy_t *
H5O_cache_chk_load(H5F_t *f, hid_t dxpl_id, haddr_t addr, void *_udata)
{
    H5O_chunk_proxy_t	*chk_proxy = NULL;     /* Chunk proxy object */
    H5O_chk_cache_ud_t *udata = (H5O_chk_cache_ud_t *)_udata;       /* User data for callback */
    H5WB_t      *wb = NULL;             /* Wrapped buffer for prefix data */
    uint8_t     chunk_buf[H5O_SPEC_READ_SIZE];       /* Buffer for speculative read */
    uint8_t     *buf;                   /* Buffer to decode */
    H5O_chunk_proxy_t	*ret_value;     /* Return value */

    FUNC_ENTER_NOAPI_NOINIT

    /* Check arguments */
    HDassert(f);
    HDassert(H5F_addr_defined(addr));
    HDassert(udata);
    HDassert(udata->oh);

    /* Allocate space for the object header data structure */
    if(NULL == (chk_proxy = H5FL_CALLOC(H5O_chunk_proxy_t)))
	HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, NULL, "memory allocation failed")

    /* Wrap the local buffer for serialized header info */
    if(NULL == (wb = H5WB_wrap(chunk_buf, sizeof(chunk_buf))))
        HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "can't wrap buffer")

    /* Get a pointer to a buffer that's large enough for serialized header */
    if(NULL == (buf = (uint8_t *)H5WB_actual(wb, udata->size)))
        HGOTO_ERROR(H5E_OHDR, H5E_NOSPACE, NULL, "can't get actual buffer")

    /* Read rest of the raw data */
    if(H5F_block_read(f, H5FD_MEM_OHDR, addr, udata->size, dxpl_id, buf) < 0)
        HGOTO_ERROR(H5E_OHDR, H5E_READERROR, NULL, "unable to read object header continuation chunk")

    /* Check if we are still decoding the object header */
    /* (as opposed to bringing a piece of it back from the file) */
    if(udata->decoding) {
        /* Sanity check */
        HDassert(udata->common.f);
        HDassert(udata->common.cont_msg_info);

        /* Parse the chunk */
        if(H5O__chunk_deserialize(udata->oh, udata->common.addr, udata->size, buf, &(udata->common), &chk_proxy->cache_info.is_dirty) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, NULL, "can't deserialize object header chunk")

        /* Set the fields for the chunk proxy */
        chk_proxy->oh = udata->oh;
        chk_proxy->chunkno = udata->oh->nchunks - 1;
    } /* end if */
    else {
        /* Sanity check */
        HDassert(udata->chunkno < udata->oh->nchunks);

        /* Set the fields for the chunk proxy */
        chk_proxy->oh = udata->oh;
        chk_proxy->chunkno = udata->chunkno;

        /* Sanity check that the chunk representation we have in memory is 
         * the same as the one being brought in from disk.
         */
        HDassert(0 == HDmemcmp(buf, chk_proxy->oh->chunk[chk_proxy->chunkno].image, chk_proxy->oh->chunk[chk_proxy->chunkno].size));
    } /* end else */

    /* Increment reference count of object header */
    if(H5O_inc_rc(udata->oh) < 0)
        HGOTO_ERROR(H5E_OHDR, H5E_CANTINC, NULL, "can't increment reference count on object header")

    /* Set return value */
    ret_value = chk_proxy;

done:
    /* Release resources */
    if(wb && H5WB_unwrap(wb) < 0)
        HDONE_ERROR(H5E_OHDR, H5E_CLOSEERROR, NULL, "can't close wrapped buffer")

    /* Release the [possibly partially initialized] object header on errors */
    if(!ret_value && chk_proxy)
        if(H5O__chunk_proxy_dest(chk_proxy) < 0)
	    HDONE_ERROR(H5E_OHDR, H5E_CANTRELEASE, NULL, "unable to destroy object header chunk proxy")

    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5O_cache_chk_load() */


/*-------------------------------------------------------------------------
 * Function:	H5O_cache_chk_flush
 *
 * Purpose:	Flushes (and destroys) an object header continuation chunk.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	Quincey Koziol
 *		koziol@hdfgroup.org
 *		Jul 12 2008
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_cache_chk_flush(H5F_t *f, hid_t dxpl_id, hbool_t destroy, haddr_t addr,
    H5O_chunk_proxy_t *chk_proxy, unsigned UNUSED * flags_ptr)
{
    herr_t ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_NOAPI_NOINIT

    /* flush */
    if(chk_proxy->cache_info.is_dirty) {
        /* Serialize messages for this chunk */
        if(H5O__chunk_serialize(f, chk_proxy->oh, chk_proxy->chunkno) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTSERIALIZE, FAIL, "unable to serialize object header continuation chunk")

        /* Write the chunk out */
        HDassert(H5F_addr_defined(chk_proxy->oh->chunk[chk_proxy->chunkno].addr));
        HDassert(H5F_addr_eq(addr, chk_proxy->oh->chunk[chk_proxy->chunkno].addr));
        if(H5F_block_write(f, H5FD_MEM_OHDR, addr, chk_proxy->oh->chunk[chk_proxy->chunkno].size, dxpl_id, chk_proxy->oh->chunk[chk_proxy->chunkno].image) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_WRITEERROR, FAIL, "unable to write object header continuation chunk to disk")

        /* Mark object header as clean now */
	chk_proxy->cache_info.is_dirty = FALSE;
    } /* end if */

    /* Destroy the object header, if requested */
    if(destroy)
        if(H5O_cache_chk_dest(f, chk_proxy) < 0)
	    HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to destroy object header continuation chunk data")

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5O_cache_chk_flush() */


/*-------------------------------------------------------------------------
 * Function:	H5O_cache_chk_dest
 *
 * Purpose:	Destroys an object header continuation chunk.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	Quincey Koziol
 *              koziol@hdfgroup.org
 *              July 12, 2008
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_cache_chk_dest(H5F_t *f, H5O_chunk_proxy_t *chk_proxy)
{
    herr_t      ret_value = SUCCEED;    /* Return value */

    FUNC_ENTER_NOAPI_NOINIT

    /* Check arguments */
    HDassert(chk_proxy);
    HDassert(chk_proxy->chunkno > 0);

    /* Verify that node is clean */
    HDassert(chk_proxy->cache_info.is_dirty == FALSE);

    /* If we're going to free the space on disk, the address must be valid */
    HDassert(!chk_proxy->cache_info.free_file_space_on_destroy || H5F_addr_defined(chk_proxy->cache_info.addr));

    /* Check for releasing file space for object header */
    if(chk_proxy->cache_info.free_file_space_on_destroy) {
        /* Release the space on disk */
        /* (XXX: Nasty usage of internal DXPL value! -QAK) */
        if(H5MF_xfree(f, H5FD_MEM_OHDR, H5AC_dxpl_id, chk_proxy->oh->chunk[chk_proxy->chunkno].addr, (hsize_t)chk_proxy->oh->chunk[chk_proxy->chunkno].size) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to free object header continuation chunk")
    } /* end if */

    /* Destroy object header chunk proxy */
    if(H5O__chunk_proxy_dest(chk_proxy) < 0)
        HGOTO_ERROR(H5E_OHDR, H5E_CANTRELEASE, FAIL, "unable to destroy object header chunk proxy")

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5O_cache_chk_dest() */


/*-------------------------------------------------------------------------
 * Function:	H5O_cache_chk_clear
 *
 * Purpose:	Mark a object header continuation chunk in memory as non-dirty.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	Quincey Koziol
 *              koziol@hdfgroup.org
 *              July 12, 2008
 *
 * Changes:     In the parallel case, there is the possibility that the
 *              the object header chunk may be flushed by different
 *              processes over the life of the computation.  Thus we must
 *              ensure that the chunk image is up to date before we mark its
 *              messages clean -- as otherwise we may overwrite valid
 *              data with a blank section of a chunk image.
 *
 *              To deal with this, I have added code to call
 *              H5O_chunk_serialize() for this chunk before we
 *              mark all messages as clean if we are not destroying the
 *              chunk.
 *
 *              Do this in the parallel case only, as the problem
 *              can only occur in this context.
 *
 *              Note that at present at least, it seems that this fix
 *              is not necessary, as we don't seem to be able to
 *              generate a dirty chunk without creating a dirty object
 *              header.  However, the object header code will be changing
 *              a lot in the near future, so I'll leave this fix in
 *              for now, unless Quincey requests otherwise.
 *
 *                                              JRM -- 10/12/10
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_cache_chk_clear(H5F_t *f, H5O_chunk_proxy_t *chk_proxy, hbool_t destroy)
{
    unsigned	u;      /* Local index variable */
    herr_t ret_value = SUCCEED;

    FUNC_ENTER_NOAPI_NOINIT

    /* Check arguments */
    HDassert(chk_proxy);

#ifdef H5_HAVE_PARALLEL
    if((chk_proxy->oh->cache_info.is_dirty) && (!destroy))
        if(H5O__chunk_serialize(f, chk_proxy->oh, chk_proxy->chunkno) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTSERIALIZE, FAIL, "unable to serialize object header chunk")
#endif /* H5_HAVE_PARALLEL */

    /* Mark messages in chunk as clean */
    for(u = 0; u < chk_proxy->oh->nmesgs; u++)
        if(chk_proxy->oh->mesg[u].chunkno == chk_proxy->chunkno)
            chk_proxy->oh->mesg[u].dirty = FALSE;

    /* Mark as clean */
    chk_proxy->cache_info.is_dirty = FALSE;

    if(destroy)
        if(H5O_cache_chk_dest(f, chk_proxy) < 0)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTFREE, FAIL, "unable to destroy object header continuation chunk data")

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* end H5O_cache_chk_clear() */


/*-------------------------------------------------------------------------
 * Function:	H5O_cache_chk_size
 *
 * Purpose:	Compute the size in bytes of the specified instance of
 *              an object header continuation chunk on disk, and return it in
 *              *len_ptr.  On failure, the value of *len_ptr is undefined.
 *
 * Return:	Non-negative on success/Negative on failure
 *
 * Programmer:	Quincey Koziol
 *              koziol@hdfgroup.org
 *              July 12, 2008
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O_cache_chk_size(const H5F_t UNUSED *f, const H5O_chunk_proxy_t *chk_proxy, size_t *size_ptr)
{
    FUNC_ENTER_NOAPI_NOINIT_NOERR

    /* check args */
    HDassert(chk_proxy);
    HDassert(size_ptr);

    /* Report the object header continuation chunk's length */
    *size_ptr = chk_proxy->oh->chunk[chk_proxy->chunkno].size;

    FUNC_LEAVE_NOAPI(SUCCEED)
} /* H5O_cache_chk_size() */


/*-------------------------------------------------------------------------
 * Function:	H5O__add_cont_msg
 *
 * Purpose:	Add information from a continuation message to the list of
 *              continuation messages in the object header
 *
 * Return:	Success: SUCCEED
 *              Failure: FAIL
 *
 * Programmer:	Quincey Koziol
 *              koziol@hdfgroup.org
 *              July 12, 2008
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O__add_cont_msg(H5O_cont_msgs_t *cont_msg_info, const H5O_cont_t *cont)
{
    size_t contno;              /* Continuation message index */
    herr_t ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_STATIC

    /* Check arguments */
    HDassert(cont_msg_info);
    HDassert(cont);

    /* Increase chunk array size, if necessary */
    if(cont_msg_info->nmsgs >= cont_msg_info->alloc_nmsgs) {
        size_t na = MAX(H5O_NCHUNKS, cont_msg_info->alloc_nmsgs * 2);        /* Double # of messages allocated */
        H5O_cont_t *x;

        if(NULL == (x = H5FL_SEQ_REALLOC(H5O_cont_t, cont_msg_info->msgs, na)))
            HGOTO_ERROR(H5E_OHDR, H5E_NOSPACE, FAIL, "memory allocation failed")
        cont_msg_info->alloc_nmsgs = na;
        cont_msg_info->msgs = x;
    } /* end if */

    /* Init the continuation message info */
    contno = cont_msg_info->nmsgs++;
    cont_msg_info->msgs[contno].addr = cont->addr;
    cont_msg_info->msgs[contno].size = cont->size;
    cont_msg_info->msgs[contno].chunkno = cont->chunkno;

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* H5O__add_cont_msg() */


/*-------------------------------------------------------------------------
 * Function:	H5O__chunk_deserialize
 *
 * Purpose:	Deserialize a chunk for an object header
 *
 * Return:	Success: SUCCEED
 *              Failure: FAIL
 *
 * Programmer:	Quincey Koziol
 *              koziol@hdfgroup.org
 *              July 12, 2008
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O__chunk_deserialize(H5O_t *oh, haddr_t addr, size_t len, const uint8_t *image,
    H5O_common_cache_ud_t *udata, hbool_t *dirty)
{
    const uint8_t *p;           /* Pointer into buffer to decode */
    uint8_t *eom_ptr;           /* Pointer to end of messages for a chunk */
    size_t curmesg;             /* Current message being decoded in object header */
    unsigned merged_null_msgs = 0;  /* Number of null messages merged together */
    unsigned chunkno;           /* Current chunk's index */
#ifndef NDEBUG
    unsigned nullcnt;           /* Count of null messages (for sanity checking gaps in chunks) */
#endif /* NDEBUG */
    herr_t ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_STATIC

    /* Check arguments */
    HDassert(oh);
    HDassert(H5F_addr_defined(addr));
    HDassert(image);
    HDassert(udata->f);
    HDassert(udata->cont_msg_info);

    /* Increase chunk array size, if necessary */
    if(oh->nchunks >= oh->alloc_nchunks) {
        size_t na = MAX(H5O_NCHUNKS, oh->alloc_nchunks * 2);        /* Double # of chunks allocated */
        H5O_chunk_t *x;

        if(NULL == (x = H5FL_SEQ_REALLOC(H5O_chunk_t, oh->chunk, na)))
            HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, FAIL, "memory allocation failed")
        oh->alloc_nchunks = na;
        oh->chunk = x;
    } /* end if */

    /* Init the chunk data info */
    chunkno = (unsigned)oh->nchunks++;
    oh->chunk[chunkno].gap = 0;
    if(chunkno == 0) {
        /* First chunk's 'image' includes room for the object header prefix */
        oh->chunk[0].addr = addr;
        oh->chunk[0].size = len + (size_t)H5O_SIZEOF_HDR(oh);
    } /* end if */
    else {
        oh->chunk[chunkno].addr = addr;
        oh->chunk[chunkno].size = len;
    } /* end else */
    if(NULL == (oh->chunk[chunkno].image = H5FL_BLK_MALLOC(chunk_image, oh->chunk[chunkno].size)))
        HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, FAIL, "memory allocation failed")

    /* Copy disk image into chunk's image */
    HDmemcpy(oh->chunk[chunkno].image, image, oh->chunk[chunkno].size);

    /* Point into chunk image to decode */
    p = oh->chunk[chunkno].image;

    /* Handle chunk 0 as special case */
    if(chunkno == 0)
        /* Skip over [already decoded] prefix */
        p += (size_t)(H5O_SIZEOF_HDR(oh) - H5O_SIZEOF_CHKSUM_OH(oh));
    /* Check for magic # on chunks > 0 in later versions of the format */
    else if(chunkno > 0 && oh->version > H5O_VERSION_1) {
        /* Magic number */
        if(HDmemcmp(p, H5O_CHK_MAGIC, (size_t)H5_SIZEOF_MAGIC))
            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "wrong object header chunk signature")
        p += H5_SIZEOF_MAGIC;
    } /* end if */

    /* Save # of messages already inspected */
    curmesg = oh->nmesgs;

    /* Decode messages from this chunk */
    eom_ptr = oh->chunk[chunkno].image + (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM_OH(oh));
#ifndef NDEBUG
    nullcnt = 0;
#endif /* NDEBUG */
    while(p < eom_ptr) {
        size_t mesgno;          /* Current message to operate on */
        size_t mesg_size;       /* Size of message read in */
        unsigned id;            /* ID (type) of current message */
        uint8_t	flags;          /* Flags for current message */
        H5O_msg_crt_idx_t crt_idx = 0;  /* Creation index for current message */

        /* Decode message prefix info */

        /* Version # */
        if(oh->version == H5O_VERSION_1)
            UINT16DECODE(p, id)
        else
            id = *p++;

        /* Check for unknown message ID getting encoded in file */
        if(id == H5O_UNKNOWN_ID)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "'unknown' message ID encoded in file?!?")

        /* Message size */
        UINT16DECODE(p, mesg_size);
        HDassert(mesg_size == H5O_ALIGN_OH(oh, mesg_size));

        /* Message flags */
        flags = *p++;
        if(flags & ~H5O_MSG_FLAG_BITS)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "unknown flag for message")
        if((flags & H5O_MSG_FLAG_SHARED) && (flags & H5O_MSG_FLAG_DONTSHARE))
            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "bad flag combination for message")
        if((flags & H5O_MSG_FLAG_WAS_UNKNOWN) && (flags & H5O_MSG_FLAG_FAIL_IF_UNKNOWN_AND_OPEN_FOR_WRITE))
            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "bad flag combination for message")
        if((flags & H5O_MSG_FLAG_WAS_UNKNOWN) && !(flags & H5O_MSG_FLAG_MARK_IF_UNKNOWN))
            HGOTO_ERROR(H5E_OHDR, H5E_CANTLOAD, FAIL, "bad flag combination for message")

        /* Reserved bytes/creation index */
        if(oh->version == H5O_VERSION_1)
            p += 3; /*reserved*/
        else {
            /* Only decode creation index if they are being tracked */
            if(oh->flags & H5O_HDR_ATTR_CRT_ORDER_TRACKED)
                UINT16DECODE(p, crt_idx);
        } /* end else */

        /* Try to detect invalidly formatted object header message that
         *  extends past end of chunk.
         */
        if(p + mesg_size > eom_ptr)
            HGOTO_ERROR(H5E_OHDR, H5E_CANTINIT, FAIL, "corrupt object header")

#ifndef NDEBUG
        /* Increment count of null messages */
        if(H5O_NULL_ID == id)
            nullcnt++;
#endif /* NDEBUG */

        /* Check for combining two adjacent 'null' messages */
        if((udata->file_intent & H5F_ACC_RDWR) &&
                H5O_NULL_ID == id && oh->nmesgs > 0 &&
                H5O_NULL_ID == oh->mesg[oh->nmesgs - 1].type->id &&
                oh->mesg[oh->nmesgs - 1].chunkno == chunkno) {

            /* Combine adjacent null messages */
            mesgno = oh->nmesgs - 1;
            oh->mesg[mesgno].raw_size += (size_t)H5O_SIZEOF_MSGHDR_OH(oh) + mesg_size;
            oh->mesg[mesgno].dirty = TRUE;
            merged_null_msgs++;
            udata->merged_null_msgs++;
        } /* end if */
        else {
            /* Check if we need to extend message table to hold the new message */
            if(oh->nmesgs >= oh->alloc_nmesgs)
                if(H5O_alloc_msgs(oh, (size_t)1) < 0)
                    HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, FAIL, "can't allocate more space for messages")

            /* Get index for message */
            mesgno = oh->nmesgs++;

            /* Initialize information about message */
            oh->mesg[mesgno].dirty = FALSE;
            oh->mesg[mesgno].flags = flags;
            oh->mesg[mesgno].crt_idx = crt_idx;
            oh->mesg[mesgno].native = NULL;
            oh->mesg[mesgno].raw = (uint8_t *)p;        /* Casting away const OK - QAK */
            oh->mesg[mesgno].raw_size = mesg_size;
            oh->mesg[mesgno].chunkno = chunkno;

            /* Point unknown messages at 'unknown' message class */
            /* (Usually from future versions of the library) */
            if(id >= NELMTS(H5O_msg_class_g) || NULL == H5O_msg_class_g[id]) {
                H5O_unknown_t *unknown;     /* Pointer to "unknown" message info */

                /* Allocate "unknown" message info */
                if(NULL == (unknown = H5FL_MALLOC(H5O_unknown_t)))
                    HGOTO_ERROR(H5E_OHDR, H5E_CANTALLOC, FAIL, "memory allocation failed")

                /* Save the original message type ID */
                *unknown = id;

                /* Save 'native' form of unknown message */
                oh->mesg[mesgno].native = unknown;

                /* Set message to "unknown" class */
                oh->mesg[mesgno].type = H5O_msg_class_g[H5O_UNKNOWN_ID];

                /* Check for "fail if unknown" message flag */
                if((udata->file_intent & H5F_ACC_RDWR) && 
                   (flags & H5O_MSG_FLAG_FAIL_IF_UNKNOWN_AND_OPEN_FOR_WRITE))
                    HGOTO_ERROR(H5E_OHDR, H5E_BADMESG, FAIL, "unknown message with 'fail if unknown' flag found")
                /* Check for "mark if unknown" message flag, etc. */
                else if((flags & H5O_MSG_FLAG_MARK_IF_UNKNOWN) &&
                        !(flags & H5O_MSG_FLAG_WAS_UNKNOWN) &&
                        (udata->file_intent & H5F_ACC_RDWR)) {

                    /* Mark the message as "unknown" */
                    /* This is a bit aggressive, since the application may
                     * never change anything about the object (metadata or
                     * raw data), but we can sort out the finer details
                     * when/if we start using the flag - QAK
                     */
                    /* Also, it's possible that this functionality may not
                     * get invoked if the object header is brought into
                     * the metadata cache in some other "weird" way, like
                     * using H5Ocopy() - QAK
                     */
                    oh->mesg[mesgno].flags |= H5O_MSG_FLAG_WAS_UNKNOWN;

                    /* Mark the message and chunk as dirty */
                    oh->mesg[mesgno].dirty = TRUE;
                    udata->mesgs_modified = TRUE;
                    *dirty = TRUE;
                } /* end if */
            } /* end if */
            else
                /* Set message class for "known" messages */
                oh->mesg[mesgno].type = H5O_msg_class_g[id];
        } /* end else */

        /* Advance decode pointer past message */
        p += mesg_size;

        /* Check for 'gap' at end of chunk */
        if((eom_ptr - p) > 0 && (eom_ptr - p) < H5O_SIZEOF_MSGHDR_OH(oh)) {
            /* Gaps can only occur in later versions of the format */
            HDassert(oh->version > H5O_VERSION_1);

            /* Gaps should only occur in chunks with no null messages */
            HDassert(nullcnt == 0);

            /* Set gap information for chunk */
            oh->chunk[chunkno].gap = (size_t)(eom_ptr - p);

            /* Increment location in chunk */
            p += oh->chunk[chunkno].gap;
        } /* end if */
    } /* end while */

    /* Check for correct checksum on chunks, in later versions of the format */
    if(oh->version > H5O_VERSION_1) {
        uint32_t stored_chksum;     /* Checksum from file */
        uint32_t computed_chksum;   /* Checksum computed in memory */

        /* Metadata checksum */
        UINT32DECODE(p, stored_chksum);

        /* Compute checksum on chunk */
        computed_chksum = H5_checksum_metadata(oh->chunk[chunkno].image, (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM), 0);

        /* Verify checksum */
        if(stored_chksum != computed_chksum)
            HGOTO_ERROR(H5E_OHDR, H5E_BADVALUE, FAIL, "incorrect metadata checksum for object header chunk")
    } /* end if */

    /* Sanity check */
    HDassert(p == oh->chunk[chunkno].image + oh->chunk[chunkno].size);

    /* Do some inspection/interpretation of new messages from this chunk */
    /* (detect continuation messages, ref. count messages, etc.) */
    while(curmesg < oh->nmesgs) {
        /* Check if next message to examine is a continuation message */
        if(H5O_CONT_ID == oh->mesg[curmesg].type->id) {
            H5O_cont_t *cont;
            unsigned ioflags = 0;   /* Flags for decode routine */

            /* Decode continuation message */
            cont = (H5O_cont_t *)(H5O_MSG_CONT->decode)(udata->f, udata->dxpl_id, NULL, 0, &ioflags, oh->mesg[curmesg].raw);
            cont->chunkno = udata->cont_msg_info->nmsgs + 1;	/*the next continuation message/chunk */

            /* Save 'native' form of continuation message */
            oh->mesg[curmesg].native = cont;

            /* Add to continuation messages left to interpret */
            if(H5O__add_cont_msg(udata->cont_msg_info, cont) < 0)
                HGOTO_ERROR(H5E_OHDR, H5E_CANTSET, FAIL, "can't add continuation message")

            /* Mark the message & chunk as dirty if the message was changed by decoding */
            if((ioflags & H5O_DECODEIO_DIRTY) && (udata->file_intent & H5F_ACC_RDWR)) {
                oh->mesg[curmesg].dirty = TRUE;
                udata->mesgs_modified = TRUE;
                *dirty = TRUE;
            } /* end if */
        } /* end if */
        /* Check if next message to examine is a ref. count message */
        else if(H5O_REFCOUNT_ID == oh->mesg[curmesg].type->id) {
            H5O_refcount_t *refcount;
            unsigned ioflags = 0;   /* Flags for decode routine */

            /* Decode ref. count message */
            HDassert(oh->version > H5O_VERSION_1);
            refcount = (H5O_refcount_t *)(H5O_MSG_REFCOUNT->decode)(udata->f, udata->dxpl_id, NULL, 0, &ioflags, oh->mesg[curmesg].raw);

            /* Save 'native' form of ref. count message */
            oh->mesg[curmesg].native = refcount;

            /* Set object header values */
            oh->has_refcount_msg = TRUE;
            oh->nlink = *refcount;

            /* Mark the message & chunk as dirty if the message was changed by decoding */
            if((ioflags & H5O_DECODEIO_DIRTY) && (udata->file_intent & H5F_ACC_RDWR)) {
                oh->mesg[curmesg].dirty = TRUE;
                udata->mesgs_modified = TRUE;
                *dirty = TRUE;
            } /* end if */
        } /* end if */
        /* Check if next message to examine is a link message */
        else if(H5O_LINK_ID == oh->mesg[curmesg].type->id) {
            /* Increment the count of link messages */
            oh->link_msgs_seen++;
        } /* end if */
        /* Check if next message to examine is an attribute message */
        else if(H5O_ATTR_ID == oh->mesg[curmesg].type->id) {
            /* Increment the count of attribute messages */
            oh->attr_msgs_seen++;
        } /* end if */

        /* Advance to next message */
        curmesg++;
    } /* end while */

    /* Mark the chunk dirty if we've merged null messages */
    if(merged_null_msgs) {
        udata->mesgs_modified = TRUE;
	*dirty = TRUE;
    } /* end if */

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* H5O__chunk_deserialize() */


/*-------------------------------------------------------------------------
 * Function:	H5O__chunk_serialize
 *
 * Purpose:	Serialize a chunk for an object header
 *
 * Return:	Success: SUCCEED
 *              Failure: FAIL
 *
 * Programmer:	Quincey Koziol
 *              koziol@hdfgroup.org
 *              July 12, 2008
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O__chunk_serialize(const H5F_t *f, H5O_t *oh, unsigned chunkno)
{
    H5O_mesg_t *curr_msg;       /* Pointer to current message being operated on */
    unsigned	u;              /* Local index variable */
    herr_t ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_STATIC

    /* Check arguments */
    HDassert(f);
    HDassert(oh);

    /* Encode any dirty messages in this chunk */
    for(u = 0, curr_msg = &oh->mesg[0]; u < oh->nmesgs; u++, curr_msg++)
        if(curr_msg->dirty && curr_msg->chunkno == chunkno)
            /* Casting away const OK -QAK */
            if(H5O_msg_flush((H5F_t *)f, oh, curr_msg) < 0)
                HGOTO_ERROR(H5E_OHDR, H5E_CANTENCODE, FAIL, "unable to encode object header message")

    /* Sanity checks */
    if(oh->version > H5O_VERSION_1)
        /* Make certain the magic # is present */
        HDassert(!HDmemcmp(oh->chunk[chunkno].image, (chunkno == 0 ? H5O_HDR_MAGIC : H5O_CHK_MAGIC), H5_SIZEOF_MAGIC));
    else
        /* Gaps should never occur in version 1 of the format */
        HDassert(oh->chunk[chunkno].gap == 0);

    /* Extra work, for later versions of the format */
    if(oh->version > H5O_VERSION_1) {
        uint32_t metadata_chksum;   /* Computed metadata checksum value */
        uint8_t	*p;                 /* Pointer into object header chunk */

        /* Check for gap in chunk & zero it out */
        if(oh->chunk[chunkno].gap)
            HDmemset((oh->chunk[chunkno].image + oh->chunk[chunkno].size) -
                (H5O_SIZEOF_CHKSUM + oh->chunk[chunkno].gap), 0, oh->chunk[chunkno].gap);

        /* Compute metadata checksum */
        metadata_chksum = H5_checksum_metadata(oh->chunk[chunkno].image, (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM), 0);

        /* Metadata checksum */
        p = oh->chunk[chunkno].image + (oh->chunk[chunkno].size - H5O_SIZEOF_CHKSUM);
        UINT32ENCODE(p, metadata_chksum);
    } /* end if */

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* H5O__chunk_serialize() */


/*-------------------------------------------------------------------------
 * Function:	H5O__chunk_proxy_dest
 *
 * Purpose:	Destroy a chunk proxy object
 *
 * Return:	Success: SUCCEED
 *              Failure: FAIL
 *
 * Programmer:	Quincey Koziol
 *              koziol@hdfgroup.org
 *              July 13, 2008
 *
 *-------------------------------------------------------------------------
 */
static herr_t
H5O__chunk_proxy_dest(H5O_chunk_proxy_t *chk_proxy)
{
    herr_t ret_value = SUCCEED; /* Return value */

    FUNC_ENTER_STATIC

    /* Check arguments */
    HDassert(chk_proxy);

    /* Decrement reference count of object header */
    if(chk_proxy->oh && H5O_dec_rc(chk_proxy->oh) < 0)
        HGOTO_ERROR(H5E_OHDR, H5E_CANTDEC, FAIL, "can't decrement reference count on object header")

    /* Release the chunk proxy object */
    chk_proxy = H5FL_FREE(H5O_chunk_proxy_t, chk_proxy);

done:
    FUNC_LEAVE_NOAPI(ret_value)
} /* H5O_chunk_proxy_dest() */