2 * Copyright (c) 1997, 1998
3 * Cybernet Corporation and Nan Yang Computer Services Limited.
6 * This software was developed as part of the NetMAX project.
8 * Written by Greg Lehey
10 * This software is distributed under the so-called ``Berkeley
13 * Redistribution and use in source and binary forms, with or without
14 * modification, are permitted provided that the following conditions
16 * 1. Redistributions of source code must retain the above copyright
17 * notice, this list of conditions and the following disclaimer.
18 * 2. Redistributions in binary form must reproduce the above copyright
19 * notice, this list of conditions and the following disclaimer in the
20 * documentation and/or other materials provided with the distribution.
21 * 3. All advertising materials mentioning features or use of this software
22 * must display the following acknowledgement:
23 * This product includes software developed by Cybernet Corporation
24 * and Nan Yang Computer Services Limited
25 * 4. Neither the name of the Companies nor the names of its contributors
26 * may be used to endorse or promote products derived from this software
27 * without specific prior written permission.
29 * This software is provided ``as is'', and any express or implied
30 * warranties, including, but not limited to, the implied warranties of
31 * merchantability and fitness for a particular purpose are disclaimed.
32 * In no event shall the company or contributors be liable for any
33 * direct, indirect, incidental, special, exemplary, or consequential
34 * damages (including, but not limited to, procurement of substitute
35 * goods or services; loss of use, data, or profits; or business
36 * interruption) however caused and on any theory of liability, whether
37 * in contract, strict liability, or tort (including negligence or
38 * otherwise) arising in any way out of the use of this software, even if
39 * advised of the possibility of such damage.
41 * $Id: vinumraid5.c,v 1.21 2001/01/09 04:21:27 grog Exp grog $
42 * $FreeBSD: src/sys/dev/vinum/vinumraid5.c,v 1.6.2.2 2001/03/13 02:59:43 grog Exp $
43 * $DragonFly: src/sys/dev/raid/vinum/vinumraid5.c,v 1.2 2003/06/17 04:28:33 dillon Exp $
45 #include <dev/vinum/vinumhdr.h>
46 #include <dev/vinum/request.h>
47 #include <sys/resourcevar.h>
50 * Parameters which describe the current transfer.
51 * These are only used for calculation, but they
52 * need to be passed to other functions, so it's
53 * tidier to put them in a struct
56 daddr_t stripebase; /* base address of stripe (1st subdisk) */
57 int stripeoffset; /* offset in stripe */
58 int stripesectors; /* total sectors to transfer in this stripe */
59 daddr_t sdbase; /* offset in subdisk of stripe base */
60 int sdcount; /* number of disks involved in this transfer */
61 daddr_t diskstart; /* remember where this transfer starts */
62 int psdno; /* number of parity subdisk */
63 int badsdno; /* number of down subdisk, if there is one */
64 int firstsdno; /* first data subdisk number */
65 /* These correspond to the fields in rqelement, sort of */
68 * Initial offset and length values for the first
71 int initoffset; /* start address of block to transfer */
72 short initlen; /* length in sectors of data transfer */
73 /* Define a normal operation */
74 int dataoffset; /* start address of block to transfer */
75 int datalen; /* length in sectors of data transfer */
76 /* Define a group operation */
77 int groupoffset; /* subdisk offset of group operation */
78 int grouplen; /* length in sectors of group operation */
79 /* Define a normal write operation */
80 int writeoffset; /* subdisk offset of normal write */
81 int writelen; /* length in sectors of write operation */
82 enum xferinfo flags; /* to check what we're doing */
83 int rqcount; /* number of elements in request */
86 enum requeststatus bre5(struct request *rq,
90 void complete_raid5_write(struct rqelement *);
91 enum requeststatus build_rq_buffer(struct rqelement *rqe, struct plex *plex);
92 void setrqebounds(struct rqelement *rqe, struct metrics *mp);
95 * define the low-level requests needed to perform
96 * a high-level I/O operation for a specific plex
99 * Return 0 if all subdisks involved in the
100 * request are up, 1 if some subdisks are not up,
101 * and -1 if the request is at least partially
102 * outside the bounds of the subdisks.
104 * Modify the pointer *diskstart to point to the
105 * end address. On read, return on the first bad
106 * subdisk, so that the caller
107 * (build_read_request) can try alternatives.
109 * On entry to this routine, the prq structures
110 * are not assigned. The assignment is performed
111 * by expandrq(). Strictly speaking, the elements
112 * rqe->sdno of all entries should be set to -1,
113 * since 0 (from bzero) is a valid subdisk number.
114 * We avoid this problem by initializing the ones
115 * we use, and not looking at the others (index >=
119 bre5(struct request *rq,
124 struct metrics m; /* most of the information */
127 struct buf *bp; /* user's bp */
128 struct rqgroup *rqg; /* the request group that we will create */
129 struct rqelement *rqe; /* point to this request information */
130 int rsectors; /* sectors remaining in this stripe */
131 int mysdno; /* another sd index in loops */
132 int rqno; /* request number */
134 rqg = NULL; /* shut up, damn compiler */
135 m.diskstart = *diskaddr; /* start of transfer */
136 bp = rq->bp; /* buffer pointer */
137 plex = &PLEX[plexno]; /* point to the plex */
140 while (*diskaddr < diskend) { /* until we get it all sorted out */
141 if (*diskaddr >= plex->length) /* beyond the end of the plex */
142 return REQUEST_EOF; /* can't continue */
144 m.badsdno = -1; /* no bad subdisk yet */
146 /* Part A: Define the request */
148 * First, calculate some sizes:
149 * The offset of the start address from
150 * the start of the stripe.
152 m.stripeoffset = *diskaddr % (plex->stripesize * (plex->subdisks - 1));
155 * The plex-relative address of the
156 * start of the stripe.
158 m.stripebase = *diskaddr - m.stripeoffset;
160 /* subdisk containing the parity stripe */
161 if (plex->organization == plex_raid5)
162 m.psdno = plex->subdisks - 1
163 - (*diskaddr / (plex->stripesize * (plex->subdisks - 1)))
166 m.psdno = plex->subdisks - 1;
169 * The number of the subdisk in which
170 * the start is located.
172 m.firstsdno = m.stripeoffset / plex->stripesize;
173 if (m.firstsdno >= m.psdno) /* at or past parity sd */
174 m.firstsdno++; /* increment it */
177 * The offset from the beginning of
178 * the stripe on this subdisk.
180 m.initoffset = m.stripeoffset % plex->stripesize;
182 /* The offset of the stripe start relative to this subdisk */
183 m.sdbase = m.stripebase / (plex->subdisks - 1);
185 m.useroffset = *diskaddr - m.diskstart; /* The offset of the start in the user buffer */
188 * The number of sectors to transfer in the
189 * current (first) subdisk.
191 m.initlen = min(diskend - *diskaddr, /* the amount remaining to transfer */
192 plex->stripesize - m.initoffset); /* and the amount left in this block */
195 * The number of sectors to transfer in this stripe
196 * is the minumum of the amount remaining to transfer
197 * and the amount left in this stripe.
199 m.stripesectors = min(diskend - *diskaddr,
200 plex->stripesize * (plex->subdisks - 1) - m.stripeoffset);
202 /* The number of data subdisks involved in this request */
203 m.sdcount = (m.stripesectors + m.initoffset + plex->stripesize - 1) / plex->stripesize;
205 /* Part B: decide what kind of transfer this will be.
207 * start and end addresses of the transfer in
210 * There are a number of different kinds of
211 * transfer, each of which relates to a
214 * 1. Normal read. All participating subdisks
215 * are up, and the transfer can be made
216 * directly to the user buffer. The bounds
217 * of the transfer are described by
218 * m.dataoffset and m.datalen. We have
219 * already calculated m.initoffset and
220 * m.initlen, which define the parameters
221 * for the first data block.
223 * 2. Recovery read. One participating
224 * subdisk is down. To recover data, all
225 * the other subdisks, including the parity
226 * subdisk, must be read. The data is
227 * recovered by exclusive-oring all the
228 * other blocks. The bounds of the
229 * transfer are described by m.groupoffset
232 * 3. A read request may request reading both
233 * available data (normal read) and
234 * non-available data (recovery read).
235 * This can be a problem if the address
236 * ranges of the two reads do not coincide:
237 * in this case, the normal read needs to
238 * be extended to cover the address range
239 * of the recovery read, and must thus be
240 * performed out of malloced memory.
242 * 4. Normal write. All the participating
243 * subdisks are up. The bounds of the
244 * transfer are described by m.dataoffset
245 * and m.datalen. Since these values
246 * differ for each block, we calculate the
247 * bounds for the parity block
248 * independently as the maximum of the
249 * individual blocks and store these values
250 * in m.writeoffset and m.writelen. This
251 * write proceeds in four phases:
253 * i. Read the old contents of each block
254 * and the parity block.
255 * ii. ``Remove'' the old contents from
256 * the parity block with exclusive or.
257 * iii. ``Insert'' the new contents of the
258 * block in the parity block, again
261 * iv. Write the new contents of the data
262 * blocks and the parity block. The data
263 * block transfers can be made directly from
266 * 5. Degraded write where the data block is
267 * not available. The bounds of the
268 * transfer are described by m.groupoffset
269 * and m.grouplen. This requires the
272 * i. Read in all the other data blocks,
273 * excluding the parity block.
275 * ii. Recreate the parity block from the
276 * other data blocks and the data to be
279 * iii. Write the parity block.
281 * 6. Parityless write, a write where the
282 * parity block is not available. This is
283 * in fact the simplest: just write the
284 * data blocks. This can proceed directly
285 * from the user buffer. The bounds of the
286 * transfer are described by m.dataoffset
289 * 7. Combination of degraded data block write
290 * and normal write. In this case the
291 * address ranges of the reads may also
292 * need to be extended to cover all
293 * participating blocks.
295 * All requests in a group transfer transfer
296 * the same address range relative to their
297 * subdisk. The individual transfers may
298 * vary, but since our group of requests is
299 * all in a single slice, we can define a
300 * range in which they all fall.
302 * In the following code section, we determine
303 * which kind of transfer we will perform. If
304 * there is a group transfer, we also decide
305 * its bounds relative to the subdisks. At
306 * the end, we have the following values:
308 * m.flags indicates the kinds of transfers
310 * m.initoffset indicates the offset of the
311 * beginning of any data operation relative
312 * to the beginning of the stripe base.
313 * m.initlen specifies the length of any data
315 * m.dataoffset contains the same value as
317 * m.datalen contains the same value as
318 * m.initlen. Initially dataoffset and
319 * datalen describe the parameters for the
320 * first data block; while building the data
321 * block requests, they are updated for each
323 * m.groupoffset indicates the offset of any
324 * group operation relative to the beginning
325 * of the stripe base.
326 * m.grouplen specifies the length of any
328 * m.writeoffset indicates the offset of a
329 * normal write relative to the beginning of
330 * the stripe base. This value differs from
331 * m.dataoffset in that it applies to the
332 * entire operation, and not just the first
334 * m.writelen specifies the total span of a
335 * normal write operation. writeoffset and
336 * writelen are used to define the parity
339 m.groupoffset = 0; /* assume no group... */
340 m.grouplen = 0; /* until we know we have one */
341 m.writeoffset = m.initoffset; /* start offset of transfer */
342 m.writelen = 0; /* nothing to write yet */
343 m.flags = 0; /* no flags yet */
344 rsectors = m.stripesectors; /* remaining sectors to examine */
345 m.dataoffset = m.initoffset; /* start at the beginning of the transfer */
346 m.datalen = m.initlen;
349 plex->multiblock++; /* more than one block for the request */
351 * If we have two transfers that don't overlap,
352 * (one at the end of the first block, the other
353 * at the beginning of the second block),
354 * it's cheaper to split them.
356 if (rsectors < plex->stripesize) {
357 m.sdcount = 1; /* just one subdisk */
358 m.stripesectors = m.initlen; /* and just this many sectors */
359 rsectors = m.initlen; /* and in the loop counter */
362 if (SD[plex->sdnos[m.psdno]].state < sd_reborn) /* is our parity subdisk down? */
363 m.badsdno = m.psdno; /* note that it's down */
364 if (bp->b_flags & B_READ) { /* read operation */
365 for (mysdno = m.firstsdno; rsectors > 0; mysdno++) {
366 if (mysdno == m.psdno) /* ignore parity on read */
368 if (mysdno == plex->subdisks) /* wraparound */
370 if (mysdno == m.psdno) /* parity, */
371 mysdno++; /* we've given already */
373 if (SD[plex->sdnos[mysdno]].state < sd_reborn) { /* got a bad subdisk, */
374 if (m.badsdno >= 0) /* we had one already, */
375 return REQUEST_DOWN; /* we can't take a second */
376 m.badsdno = mysdno; /* got the first */
377 m.groupoffset = m.dataoffset; /* define the bounds */
378 m.grouplen = m.datalen;
379 m.flags |= XFR_RECOVERY_READ; /* we need recovery */
380 plex->recovered_reads++; /* count another one */
382 m.flags |= XFR_NORMAL_READ; /* normal read */
384 /* Update the pointers for the next block */
385 m.dataoffset = 0; /* back to the start of the stripe */
386 rsectors -= m.datalen; /* remaining sectors to examine */
387 m.datalen = min(rsectors, plex->stripesize); /* amount that will fit in this block */
389 } else { /* write operation */
390 for (mysdno = m.firstsdno; rsectors > 0; mysdno++) {
391 if (mysdno == m.psdno) /* parity stripe, we've dealt with that */
393 if (mysdno == plex->subdisks) /* wraparound */
395 if (mysdno == m.psdno) /* parity, */
396 mysdno++; /* we've given already */
398 sd = &SD[plex->sdnos[mysdno]];
399 if (sd->state != sd_up) {
400 enum requeststatus s;
402 s = checksdstate(sd, rq, *diskaddr, diskend); /* do we need to change state? */
403 if (s && (m.badsdno >= 0)) { /* second bad disk, */
406 * If the parity disk is down, there's
407 * no recovery. We make all involved
408 * subdisks stale. Otherwise, we
409 * should be able to recover, but it's
410 * like pulling teeth. Fix it later.
412 for (sdno = 0; sdno < m.sdcount; sdno++) {
413 struct sd *sd = &SD[plex->sdnos[sdno]];
414 if (sd->state >= sd_reborn) /* sort of up, */
415 set_sd_state(sd->sdno, sd_stale, setstate_force); /* make it stale */
417 return s; /* and crap out */
419 m.badsdno = mysdno; /* note which one is bad */
420 m.flags |= XFR_DEGRADED_WRITE; /* we need recovery */
421 plex->degraded_writes++; /* count another one */
422 m.groupoffset = m.dataoffset; /* define the bounds */
423 m.grouplen = m.datalen;
425 m.flags |= XFR_NORMAL_WRITE; /* normal write operation */
426 if (m.writeoffset > m.dataoffset) { /* move write operation lower */
427 m.writelen = max(m.writeoffset + m.writelen,
428 m.dataoffset + m.datalen)
430 m.writeoffset = m.dataoffset;
432 m.writelen = max(m.writeoffset + m.writelen,
433 m.dataoffset + m.datalen)
437 /* Update the pointers for the next block */
438 m.dataoffset = 0; /* back to the start of the stripe */
439 rsectors -= m.datalen; /* remaining sectors to examine */
440 m.datalen = min(rsectors, plex->stripesize); /* amount that will fit in this block */
442 if (m.badsdno == m.psdno) { /* got a bad parity block, */
443 struct sd *psd = &SD[plex->sdnos[m.psdno]];
445 if (psd->state == sd_down)
446 set_sd_state(psd->sdno, sd_obsolete, setstate_force); /* it's obsolete now */
447 else if (psd->state == sd_crashed)
448 set_sd_state(psd->sdno, sd_stale, setstate_force); /* it's stale now */
449 m.flags &= ~XFR_NORMAL_WRITE; /* this write isn't normal, */
450 m.flags |= XFR_PARITYLESS_WRITE; /* it's parityless */
451 plex->parityless_writes++; /* count another one */
455 /* reset the initial transfer values */
456 m.dataoffset = m.initoffset; /* start at the beginning of the transfer */
457 m.datalen = m.initlen;
459 /* decide how many requests we need */
460 if (m.flags & (XFR_RECOVERY_READ | XFR_DEGRADED_WRITE))
461 /* doing a recovery read or degraded write, */
462 m.rqcount = plex->subdisks; /* all subdisks */
463 else if (m.flags & XFR_NORMAL_WRITE) /* normal write, */
464 m.rqcount = m.sdcount + 1; /* all data blocks and the parity block */
465 else /* parityless write or normal read */
466 m.rqcount = m.sdcount; /* just the data blocks */
468 /* Part C: build the requests */
469 rqg = allocrqg(rq, m.rqcount); /* get a request group */
470 if (rqg == NULL) { /* malloc failed */
471 bp->b_error = ENOMEM;
472 bp->b_flags |= B_ERROR;
473 return REQUEST_ENOMEM;
475 rqg->plexno = plexno;
476 rqg->flags = m.flags;
477 rqno = 0; /* index in the request group */
479 /* 1: PARITY BLOCK */
481 * Are we performing an operation which requires parity? In that case,
482 * work out the parameters and define the parity block.
483 * XFR_PARITYOP is XFR_NORMAL_WRITE | XFR_RECOVERY_READ | XFR_DEGRADED_WRITE
485 if (m.flags & XFR_PARITYOP) { /* need parity */
486 rqe = &rqg->rqe[rqno]; /* point to element */
487 sd = &SD[plex->sdnos[m.psdno]]; /* the subdisk in question */
488 rqe->rqg = rqg; /* point back to group */
489 rqe->flags = (m.flags | XFR_PARITY_BLOCK | XFR_MALLOCED) /* always malloc parity block */
490 &~(XFR_NORMAL_READ | XFR_PARITYLESS_WRITE); /* transfer flags without data op stuf */
491 setrqebounds(rqe, &m); /* set up the bounds of the transfer */
492 rqe->sdno = sd->sdno; /* subdisk number */
493 rqe->driveno = sd->driveno;
494 if (build_rq_buffer(rqe, plex)) /* build the buffer */
495 return REQUEST_ENOMEM; /* can't do it */
496 rqe->b.b_flags |= B_READ; /* we must read first */
497 m.sdcount++; /* adjust the subdisk count */
498 rqno++; /* and point to the next request */
502 * Now build up requests for the blocks required
503 * for individual transfers
505 for (mysdno = m.firstsdno; rqno < m.sdcount; mysdno++, rqno++) {
506 if (mysdno == m.psdno) /* parity, */
507 mysdno++; /* we've given already */
508 if (mysdno == plex->subdisks) /* got to the end, */
509 mysdno = 0; /* wrap around */
510 if (mysdno == m.psdno) /* parity, */
511 mysdno++; /* we've given already */
513 rqe = &rqg->rqe[rqno]; /* point to element */
514 sd = &SD[plex->sdnos[mysdno]]; /* the subdisk in question */
515 rqe->rqg = rqg; /* point to group */
516 if (m.flags & XFR_NEEDS_MALLOC) /* we need a malloced buffer first */
517 rqe->flags = m.flags | XFR_DATA_BLOCK | XFR_MALLOCED; /* transfer flags */
519 rqe->flags = m.flags | XFR_DATA_BLOCK; /* transfer flags */
520 if (mysdno == m.badsdno) { /* this is the bad subdisk */
521 rqg->badsdno = rqno; /* note which one */
522 rqe->flags |= XFR_BAD_SUBDISK; /* note that it's dead */
524 * we can't read or write from/to it,
525 * but we don't need to malloc
527 rqe->flags &= ~(XFR_MALLOCED | XFR_NORMAL_READ | XFR_NORMAL_WRITE);
529 setrqebounds(rqe, &m); /* set up the bounds of the transfer */
530 rqe->useroffset = m.useroffset; /* offset in user buffer */
531 rqe->sdno = sd->sdno; /* subdisk number */
532 rqe->driveno = sd->driveno;
533 if (build_rq_buffer(rqe, plex)) /* build the buffer */
534 return REQUEST_ENOMEM; /* can't do it */
535 if ((m.flags & XFR_PARITYOP) /* parity operation, */
536 &&((m.flags & XFR_BAD_SUBDISK) == 0)) /* and not the bad subdisk, */
537 rqe->b.b_flags |= B_READ; /* we must read first */
539 /* Now update pointers for the next block */
540 *diskaddr += m.datalen; /* skip past what we've done */
541 m.stripesectors -= m.datalen; /* deduct from what's left */
542 m.useroffset += m.datalen; /* and move on in the user buffer */
543 m.datalen = min(m.stripesectors, plex->stripesize); /* and recalculate */
544 m.dataoffset = 0; /* start at the beginning of next block */
548 * 3: REMAINING BLOCKS FOR RECOVERY
549 * Finally, if we have a recovery operation, build
550 * up transfers for the other subdisks. Follow the
551 * subdisks around until we get to where we started.
552 * These requests use only the group parameters.
554 if ((rqno < m.rqcount) /* haven't done them all already */
555 &&(m.flags & (XFR_RECOVERY_READ | XFR_DEGRADED_WRITE))) {
556 for (; rqno < m.rqcount; rqno++, mysdno++) {
557 if (mysdno == m.psdno) /* parity, */
558 mysdno++; /* we've given already */
559 if (mysdno == plex->subdisks) /* got to the end, */
560 mysdno = 0; /* wrap around */
561 if (mysdno == m.psdno) /* parity, */
562 mysdno++; /* we've given already */
564 rqe = &rqg->rqe[rqno]; /* point to element */
565 sd = &SD[plex->sdnos[mysdno]]; /* the subdisk in question */
566 rqe->rqg = rqg; /* point to group */
568 rqe->sdoffset = m.sdbase + m.groupoffset; /* start of transfer */
569 rqe->dataoffset = 0; /* for tidiness' sake */
570 rqe->groupoffset = 0; /* group starts at the beginining */
572 rqe->grouplen = m.grouplen;
573 rqe->buflen = m.grouplen;
574 rqe->flags = (m.flags | XFR_MALLOCED) /* transfer flags without data op stuf */
576 rqe->sdno = sd->sdno; /* subdisk number */
577 rqe->driveno = sd->driveno;
578 if (build_rq_buffer(rqe, plex)) /* build the buffer */
579 return REQUEST_ENOMEM; /* can't do it */
580 rqe->b.b_flags |= B_READ; /* we must read first */
584 * We need to lock the address range before
585 * doing anything. We don't have to be
586 * performing a recovery operation: somebody
587 * else could be doing so, and the results could
588 * influence us. Note the fact here, we'll perform
589 * the lock in launch_requests.
591 rqg->lockbase = m.stripebase;
592 if (*diskaddr < diskend) /* didn't finish the request on this stripe */
593 plex->multistripe++; /* count another one */
599 * Helper function for rqe5: adjust the bounds of
600 * the transfers to minimize the buffer
603 * Each request can handle two of three different
606 * 1. The range described by the parameters
607 * dataoffset and datalen, for normal read or
609 * 2. The range described by the parameters
610 * groupoffset and grouplen, for recovery read
611 * and degraded write.
612 * 3. For normal write, the range depends on the
613 * kind of block. For data blocks, the range
614 * is defined by dataoffset and datalen. For
615 * parity blocks, it is defined by writeoffset
618 * In order not to allocate more memory than
619 * necessary, this function adjusts the bounds
620 * parameter for each request to cover just the
621 * minimum necessary for the function it performs.
622 * This will normally vary from one request to the
625 * Things are slightly different for the parity
626 * block. In this case, the bounds defined by
627 * mp->writeoffset and mp->writelen also play a
628 * rĂ´le. Select this case by setting the
629 * parameter forparity != 0
632 setrqebounds(struct rqelement *rqe, struct metrics *mp)
634 /* parity block of a normal write */
635 if ((rqe->flags & (XFR_NORMAL_WRITE | XFR_PARITY_BLOCK))
636 == (XFR_NORMAL_WRITE | XFR_PARITY_BLOCK)) { /* case 3 */
637 if (rqe->flags & XFR_DEGRADED_WRITE) { /* also degraded write */
639 * With a combined normal and degraded write, we
640 * will zero out the area of the degraded write
641 * in the second phase, so we don't need to read
642 * it in. Unfortunately, we need a way to tell
643 * build_request_buffer the size of the buffer,
644 * and currently that's the length of the read.
645 * As a result, we read everything, even the stuff
646 * that we're going to nuke.
649 if (mp->groupoffset < mp->writeoffset) { /* group operation starts lower */
650 rqe->sdoffset = mp->sdbase + mp->groupoffset; /* start of transfer */
651 rqe->dataoffset = mp->writeoffset - mp->groupoffset; /* data starts here */
652 rqe->groupoffset = 0; /* and the group at the beginning */
653 } else { /* individual data starts first */
654 rqe->sdoffset = mp->sdbase + mp->writeoffset; /* start of transfer */
655 rqe->dataoffset = 0; /* individual data starts at the beginning */
656 rqe->groupoffset = mp->groupoffset - mp->writeoffset; /* group starts here */
658 rqe->datalen = mp->writelen;
659 rqe->grouplen = mp->grouplen;
660 } else { /* just normal write (case 3) */
661 rqe->sdoffset = mp->sdbase + mp->writeoffset; /* start of transfer */
662 rqe->dataoffset = 0; /* degradation starts at the beginning */
663 rqe->groupoffset = 0; /* for tidiness' sake */
664 rqe->datalen = mp->writelen;
667 } else if (rqe->flags & XFR_DATAOP) { /* data operation (case 1 or 3) */
668 if (rqe->flags & XFR_GROUPOP) { /* also a group operation (case 2) */
669 if (mp->groupoffset < mp->dataoffset) { /* group operation starts lower */
670 rqe->sdoffset = mp->sdbase + mp->groupoffset; /* start of transfer */
671 rqe->dataoffset = mp->dataoffset - mp->groupoffset; /* data starts here */
672 rqe->groupoffset = 0; /* and the group at the beginning */
673 } else { /* individual data starts first */
674 rqe->sdoffset = mp->sdbase + mp->dataoffset; /* start of transfer */
675 rqe->dataoffset = 0; /* individual data starts at the beginning */
676 rqe->groupoffset = mp->groupoffset - mp->dataoffset; /* group starts here */
678 rqe->datalen = mp->datalen;
679 rqe->grouplen = mp->grouplen;
680 } else { /* just data operation (case 1) */
681 rqe->sdoffset = mp->sdbase + mp->dataoffset; /* start of transfer */
682 rqe->dataoffset = 0; /* degradation starts at the beginning */
683 rqe->groupoffset = 0; /* for tidiness' sake */
684 rqe->datalen = mp->datalen;
687 } else { /* just group operations (case 2) */
688 rqe->sdoffset = mp->sdbase + mp->groupoffset; /* start of transfer */
689 rqe->dataoffset = 0; /* for tidiness' sake */
690 rqe->groupoffset = 0; /* group starts at the beginining */
692 rqe->grouplen = mp->grouplen;
694 rqe->buflen = max(rqe->dataoffset + rqe->datalen, /* total buffer length */
695 rqe->groupoffset + rqe->grouplen);
697 /* Local Variables: */
698 /* fill-column: 50 */