Import Upstream version 1.8.5
[hcoop/debian/openafs.git] / doc / txt / vldb.txt
1
2 This document describes version 4 of the OpenAFS Volume Location Database
3 (VLDB) file format.
4
5
6 VLDB file layout
7
8 The vldb.DB0 file consists of 64 octet ubik header, followed by a 132,120 octet
9 vldb header, followed a variable number of vldb records. Records are either a
10 148 octet volume location (vl) entry or a 8192 octet multi-homed (mh) extension
11 block. A bit flag at a fixed offset of each record specifies the record type.
12 A field in the vldb header indicates the location of the last record. Any data
13 in the file following the last record is ignored.
14
15
16 Ubik header
17
18 The vldb.DB0 file begins with a 64 octet ubik header. All fields are in
19 network byte order. Only the first 16 octets of the ubik header are used. The
20 unused fields should always be zero. The first 16 octets of the ubik header
21 contain the representation of a struct ubik_hdr, with all the fields in network
22 byte order:
23
24 0 1 2 3
25 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
26 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
27 | ubik_magic |
28 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
29 | padding | header_size |
30 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
31 | epoch |
32 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
33 | counter |
34 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
35 | [unused] |
36 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
37 | [unused] |
38 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
39 | [unused] |
40 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
41 | [unused] |
42 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
43 | [unused] |
44 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
45 | [unused] |
46 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
47 | [unused] |
48 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
49 | [unused] |
50 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
51 | [unused] |
52 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
53 | [unused] |
54 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
55 | [unused] |
56 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
57 | [unused] |
58 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
59 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
60 0 1 2 3
61
62 magic is the ubik file identification. It should always be 0x00354545.
63
64 pad1 is unused, should always be 0
65
66 header_size is the size of the ubik header (including unused space), should always
67 be 0x40
68
69 epoch is the ubik quorum epoch value.
70
71 counter is the ubik counter for transactions and updates.
72
73 unused space should always be zero.
74
75
76 The ubik header is not exposed through the VL_ RPC package, and as such is not
77 considered to be part of the logical VLDB database.
78
79 Subsequent discussion will refer to VLDB addresses, or simply addresses. A
80 VLDB address is a logical offset to a data within the VLDB. The physical file
81 offset of data referenced by a VLDB address is the VLDB address plus the size
82 of the ubik header (64 octets).
83
84
85 VLDB header
86
87 The VLDB header follows the ubik_header. It is the logical beginning of the
88 VLDB. The VLDB header is 132120 octets in size. The majority of this space
89 contains four hash tables enabling quick lookups of volumes by name and id.
90 All integer fields are stored in network byte order.
91
92 The layout of the VLDB header is:
93
94 0 1 2 3
95 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
96 octets +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
97 0 | version |
98 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
99 4 | headersize |
100 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
101 8 | freePtr |
102 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
103 12 | eofPtr |
104 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
105 16 | allocs |
106 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
107 20 | frees |
108 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
109 24 | MaxVolumeId |
110 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
111 28 | TotalEntries[0] (rw) |
112 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
113 32 | TotalEntries[1] (ro) |
114 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
115 36 | TotalEntries[2] (bk) |
116 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
117 40 | IpMappedAddr |
118 ~ ... ~
119 1056 | |
120 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
121 1060 | VolnameHash |
122 ~ ... ~
123 33820 | |
124 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
125 33824 | VolidHash[0] (rw) |
126 ~ ... ~
127 | |
128 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
129 | VolidHash[1] (ro) |
130 ~ ... ~
131 | |
132 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
133 | VolidHash[2] (bk) |
134 ~ ... ~
135 132112 | |
136 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
137 132116 | SIT |
138 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
139 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
140 0 1 2 3
141
142 vldbversion is the vldb disk format version number. This document describes
143 version 4.
144
145 Note: The OpenAFS vlserver creates empty vldb files as version 3, and
146 converts the vldb to version 4 in place the first time a fileserver
147 UUID is registered.
148
149 headersize is the size in octets of the vldb header, currently 0x020418 (132120)
150
151 freePtr is the logical address in octets of the first in a linked list of
152 unused vldb entries in the vldb database file (that is the first logical hole
153 in the database file). This value is zero if the database is densely packed.
154 The physical file offset to the first free entry is the freePtr value plus the
155 size of the ubik header (64 octets). Every free vl entry in the vldb should be
156 on the free list. The nextIdHash[0] vl entry field holds the address of the
157 next vl entry on the free list.
158
159 eofPtr is the logical address in octets of the end of the database file. When a
160 new entry is created that extends the database file, it will be created at this
161 logical index.The physical file offset to the end of the database file eofPtr
162 value plus the size of the ubik header (64 octets).
163
164 allocs is the number of calls to AllocBlock(), for statistical purposes.
165
166 frees is the number of calls to FreeBlock(), for statistical purposes.
167
168 MaxVolumeId is the largest volume id allocated. It is incremented every time
169 a volume is created.
170
171 TotalEntries[0] is the number of read-write volume entries.
172
173 TotalEntries[1] is the number of read/only volume entries.
174
175 TotalEntries[2] is the number of backup volume entries.
176
177 IpMappedAddr maps vl entry serverNumbers to file server information. The vl
178 entry serverNumber field is used as an offset into the IpMappedAddr table. The
179 IpMappedaddr is a table of 255 records, one for each possible serverNumber,
180 from 0 to 254. Each record is a 32 bit integer in network byte order. Empty
181 records should be zero filled.
182
183 IpMappedAddr records hold either a reference to a mh entry or a single IPv4
184 address. Records which contain 0xFF in the first octet are references to mh
185 entries. Non-zero records which do not contain 0xFF in the first octet hold a
186 single IPv4 address in network byte order.
187
188 The format of a reference to a mh entry is:
189
190 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
191 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
192 | 0xFF | base | index |
193 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
194
195 0xFF in the first octet indicates the record contains a multi-homed entry
196 reference, instead of an IPv4 address.
197
198 base is the mh extension block number; supported range is 0 to 3.
199
200 index is the index to the mh entry within the mh extension block; supported range
201 is 1 to 63. (Index of 0 is reserved for the mh extension block header.)
202
203 Following the index are four hash tables, each containing 8191 (a prime number)
204 32-bit entries in network byte order. Each entry represents a hash bucket and
205 holds the address of the vl entry at the head of the hash chain, or zero to
206 indicate an empty hash bucket. Every vl entry which is not free should be in
207 all four hashes.
208
209 VolnameHash is the hash table for searches by volume name. The nextNameHash
210 field at the head of the chain holds the address of the next vl entry in the
211 hash chain.
212
213 The NameHash hash function is targetted for ASCII text and is similar to the
214 PRDB name hash function. Each octet of the volume name is treated as an
215 unsigned integer from which 63 (decimal) is subtracted, and the resulting
216 stream of integers is used as the coefficients of a power series with base 63
217 (decimal), with the least significant coefficient appearing first.
218
219 For example, for a volume name string string of "abc", which is the stream
220 of octets (in decimal):
221
222 97 98 99
223
224 then the power series used in the hash function calculation would be
225 (all numbers in decimal):
226
227 34 + (35 * 63) + (36 * 63**2)
228
229 The value of this power series is stored in an unsigned 32-bit integer, and as
230 such is implicitly computed modulo 2**32. The remainder modulo 8191 (the size
231 of the hash table) of this 32-bit value is used as the index into the hash
232 table for this name entry. (This hash function can be easily implemented
233 iteratively.)
234
235
236 VolidHash[0] is the hash table for searches by read-write volume ID. The
237 nextIdHash[0] field at the head of the chain holds the address of the next vl
238 entry in the hash chain.
239
240 VolidHash[1] is the read-only volume ID to vldb entry hash table. The
241 nextIdHash[1] field at the head of the chain holds the address of the next vl
242 entry in the hash chain.
243
244 VolidHash[2] is the backup volume ID to vldb entry hash table. The
245 nextIdHash[2] field at the head of the chain holds the address of the next vl
246 entry in the hash chain.
247
248 The VolidHash hash function the remainder modulo 8191 (the size of the hash
249 table) of the absolute value of the volume id.
250
251
252 SIT holds the logical address of the first multi-homed extension block in the
253 vldb. Each multi-homed extension block holds 4 logical addresses to additional
254 multi-homed extension blocks.
255
256
257 VLDB Records
258
259 VLDB Records follow immediately after the VLDB header. Each record is either a
260 148 octet sized volume location (vl) entry or a 8192 octet sized multi-homed
261 (mh) extension block. A bit flag at a fixed offset specifies the record type.
262
263 Note: The mh extension block size is *not* a multiple of the
264 vl entry size.
265
266 The only invariant field is the single bit field which indicates the
267 record type:
268
269 0 1 2 3
270 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
271 octets +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
272 0 | [record-specific] |
273 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
274 | [record-specific] |
275 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
276 | [record-specific] |
277 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
278 12 | [record-specific-flags] |C| ... |
279 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
280 | [record-specific] |
281 ~ ... ~
282 | |
283 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
284
285 C is the continuation block flag (VLCONTBLOCK). A value of 0 indicates the
286 record is a 148 octet vl entry. A value of 1 indicates the record is a 8192
287 octet mh extension block.
288
289
290 VL Entry
291
292 The 148 octet vl entry maps a volume group to a set of file server locations
293 for each volume in the volume group. A volume group consists of a single
294 read-write volume, zero or one backup volumes, zero or more read-only volumes,
295 and zero or one temporary clone volumes.
296
297 The vl entry also holds information for volume administration.
298
299 All integer fields are in network byte order.
300
301 The layout of the vl entry is:
302
303 0 1 2 3
304 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
305 octets +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
306 0 | volumeId[0] (rw) |
307 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
308 | volumeId[1] (ro) |
309 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
310 | volumeId[2] (bk) |
311 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
312 12 | flags |
313 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
314 | LockAfsId |
315 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
316 | LockAfsTimestamp |
317 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
318 | cloneId |
319 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
320 | nextIdHash[0] (rw)/(free) |
321 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
322 | nextIdHash[1] (ro) |
323 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
324 | nextIdHash[2] (bk) |
325 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
326 40 | nextNameHash |
327 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
328 44 | name |
329 + +
330 | |
331 ~ ... ~
332 | |
333 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
334 108 | | serverNumber table |
335 +-+-+-+-+-+-+-+-+ +
336 112 | |
337 + +
338 | |
339 + +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
340 120 | | |
341 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
342 124 | serverPartition table |
343 + +
344 | |
345 + +-+-+-+-+-+-+-+-+
346 132 | | |
347 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
348 136 | serverFlags table |
349 + +
350 | |
351 + +
352 144 | |
353 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
354 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
355
356
357 volumeId[0] is the volume id allocated for the read-write volume in this volume
358 group. (The VLF_RWEXITS flag is set when the read-write volume is created.)
359
360 volumeId[1] is the volume id allocated for read-only volumes in this volume
361 group. This number is allocated when the entry is created. (The VLF_ROEXISTS
362 flag is set when a read-only volume is created.)
363
364 volumeId[2] is the volume id allocated for the backup volume in this volume
365 group, if one. This number is allocated when the entry is created. (The
366 VLF_BACKEXISTS flag is set when a backup volume is created.)
367
368 flags is a bitmap which indicates the vl entry state:
369
370 0x0001 VLFREE indicates this entry is on the free list
371 0x0002 VLDELETE indicates this entry is deleted
372 0x0004 VLLOCKED not used; always zero
373 0x0008 VLCONTBLOCK always zero in vl entries
374 0x0010 VLOP_MOVE locked for a move operation
375 0x0020 VLOP_RELEASE locked for a release operation
376 0x0040 VLOP_BACKUP locked for a backup clone operation
377 0x0080 VLOP_DELETE locked for a delete or addsite operation
378 0x0100 VLOP_DUMP locked for a dump or restore operation
379 0x1000 VLF_RWEXISTS this group has a read-write volume
380 0x2000 VLF_ROEXISTS this group has at least one read-only volume
381 0x4000 VLF_BACKEXISTS this group has a backup clone
382 0x8000 VLF_DFSFILESET not used; always cleared
383
384 High order bits of the flags field are reserved and should always be zero.
385
386 LockAfsId is not used. This field is reserved to hold the id of the operator
387 who locked the entry for a volume operation.
388
389 LockTimestamp is the time stamp on the entry lock.
390
391 cloneId is the volume id of the temporary clone volume, which may be
392 created during volume operations.
393
394 nextIdHash[0] has a dual role. The nextIdHash[0] is the logical address of the
395 next vl entry on the read-write volume id hash chain when the VLFREE flag is
396 unset. The nextIdHash[0] field is the logical address of the next vl entry on
397 the free list when the VLFREE flag is set.
398
399 nextIdHash[1] is the logical address of the next vl entry on the
400 read-only volume id hash chain.
401
402 nextIdHash[2] is the logical address of the next vl entry on the backup
403 volume id hash chain.
404
405 nextNameHash the logical address of the next vl entry on the volume name
406 hash chain.
407
408 name is a 65 octet field which holds the volume name, as a null
409 terminated string.
410
411 serverNumber, serverPartition, and serverFlags fields form a 13 row by 3
412 column table. Each row describes a volume site. Empty rows are filled with
413 0xFF instead of zero.
414
415 serverNumber is a number from 0 to 254. The IpMappedAddr record at the
416 serverNumber offset has a reference to a multi-homed (mh) entry. The mh entry
417 holds the fileserver uuid and one or more IPv4 addresses of the fileserver.
418
419 serverPartition is a number from 0 to 255 which represents a file server
420 partition, from /vicepa to /vicepih.
421
422 serverFlags indicates the state of the volume site:
423
424 0x01 VLSF_NEWREPSITE read-only volume added to vldb, but not released yet
425 0x02 VLSF_ROVOL a read-only volume is present at this location (see Notes)
426 0x04 VLSF_RWVOL a read-write volume is present at this location (see Notes)
427 0x08 VLSF_BACKVOL a backup volume is present at this location (see Notes)
428 0x10 VLSF_UUID not used in the vldb; always zero
429 0x20 VLSF_DONTUSE out of date read-only volume
430 0x40 VLSF_RWREPLICA reserved for volume is a read-write replica
431
432 Notes:
433
434 1. In practice, one, and only one, of the VLSF_ROVOL, VLSF_RWVOL, VLSF_BACKVOL
435 flags are set per table row.
436
437 2. In practice, the VLSF_BACKVOL flag is not used. Instead the VLF_BACKEXISTS
438 is set in the vl entry to indicate a backup clone is present on the same
439 fileserver and partition as the read-write volume. This saves an entry
440 in the table to allow for more read-only sites.
441
442
443 Multi-homed Extension Block
444
445 Multi-homed extension blocks are 8192 octets in size. The first 128 octets hold
446 a header, which is mostly unused. The header is immediately followed by 63 mh
447 entry slots, each 128 octets in size.
448
449 Up to 4 blocks may be present in the vldb. The address of the first block is
450 held in the SIT field of the vldb header. Addresses of the first and
451 additional blocks are held in the contaddr field of the first block.
452
453 Note: In the current format, the vldb is limited to 4 blocks, and 63 mh entries
454 per block, which means the vldb is limited to 252 different mh servers, which
455 is three less than the maximum number of server numbers (255).
456
457
458 Multi-homed Extension Block Header
459
460 The layout of the mh extension block header is:
461
462 0 1 2 3
463 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
464 octets +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
465 0 | count |
466 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
467 4 | reserved[0] |
468 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
469 8 | reserved[1] |
470 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
471 12 | flags |
472 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
473 16 | contaddr[0] |
474 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
475 20 | contaddr[1] |
476 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
477 24 | contaddr[2] |
478 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
479 28 | contaddr[3] |
480 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
481 32 | reserved |
482 + +
483 | |
484 ~ ... ~
485 124 | |
486 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
487
488 count is not used.
489
490 reserved[0], reserved[1] should always be zero.
491
492 flags must have the VLCONTBLOCK bit set to indicate this is a 8192 octet
493 mh extension block. All other bits in this field should be zero.
494
495 contaddrs is a table of the addresses of the mh extension blocks, including
496 the first block.
497
498 reserved should always be zero.
499
500
501 Multi-homed Entry
502
503 The mh entry contains information for a single file server. Each mh entry
504 is 128 octets in size.
505
506 0 1 2 3
507 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
508 octets +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
509 0 | uuid.time_low |
510 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
511 4 | uuid.time_mid | uuid.time_hi_and_version |
512 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
513 8 | uuid.clock_hi | uuid.clock_lo | uuid.node |
514 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
515 12 | |
516 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
517 16 | uniquifier |
518 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
519 20 | addrs[0] |
520 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
521 24 | addrs[1] |
522 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
523 28 | addrs[2] |
524 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
525 32 | addrs[3] |
526 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
527 36 | addrs[4] |
528 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
529 40 | addrs[5] |
530 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
531 44 | addrs[6] |
532 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
533 48 | addrs[7] |
534 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
535 52 | addrs[8] |
536 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
537 56 | addrs[9] |
538 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
539 60 | addrs[10] |
540 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
541 64 | addrs[11] |
542 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
543 68 | addrs[12] |
544 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
545 72 | addrs[13] |
546 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
547 76 | addrs[14] |
548 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
549 80 | flags |
550 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
551 84 | reserved |
552 ~ ... ~
553 124 | |
554 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
555
556
557 uuid is the universal unique id the fileserver used when registering
558 with the vldb.
559
560 uniquifier is a serial number of the mh entry. The first mh entry is assigned a
561 uniquifier of 1. The uniquifier is incremented each time its containing entry
562 is modified.
563
564 addrs[0..14] holds a list of IPv4 addresses for this fileserver, each in
565 network byte order. Zero indicates an empty slot.
566
567 flags is reserved and should always be zero.
568
569 reserved should always be zero.
570