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freebsd/sys/dev/vinum/vinumraid5.c
Greg Lehey 78f25040af Cosmetics.
2000-05-11 07:25:36 +00:00

700 lines
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/*-
* Copyright (c) 1997, 1998
* Cybernet Corporation and Nan Yang Computer Services Limited.
* All rights reserved.
*
* This software was developed as part of the NetMAX project.
*
* Written by Greg Lehey
*
* This software is distributed under the so-called ``Berkeley
* License'':
*
* Redistribution and use in source and binary forms, with or without
* modification, are permitted provided that the following conditions
* are met:
* 1. Redistributions of source code must retain the above copyright
* notice, this list of conditions and the following disclaimer.
* 2. Redistributions in binary form must reproduce the above copyright
* notice, this list of conditions and the following disclaimer in the
* documentation and/or other materials provided with the distribution.
* 3. All advertising materials mentioning features or use of this software
* must display the following acknowledgement:
* This product includes software developed by Cybernet Corporation
* and Nan Yang Computer Services Limited
* 4. Neither the name of the Companies nor the names of its contributors
* may be used to endorse or promote products derived from this software
* without specific prior written permission.
*
* This software is provided ``as is'', and any express or implied
* warranties, including, but not limited to, the implied warranties of
* merchantability and fitness for a particular purpose are disclaimed.
* In no event shall the company or contributors be liable for any
* direct, indirect, incidental, special, exemplary, or consequential
* damages (including, but not limited to, procurement of substitute
* goods or services; loss of use, data, or profits; or business
* interruption) however caused and on any theory of liability, whether
* in contract, strict liability, or tort (including negligence or
* otherwise) arising in any way out of the use of this software, even if
* advised of the possibility of such damage.
*
* $Id: vinumraid5.c,v 1.20 2000/05/10 22:31:38 grog Exp grog $
* $FreeBSD$
*/
#include <dev/vinum/vinumhdr.h>
#include <dev/vinum/request.h>
#include <sys/resourcevar.h>
/*
* Parameters which describe the current transfer.
* These are only used for calculation, but they
* need to be passed to other functions, so it's
* tidier to put them in a struct
*/
struct metrics {
daddr_t stripebase; /* base address of stripe (1st subdisk) */
int stripeoffset; /* offset in stripe */
int stripesectors; /* total sectors to transfer in this stripe */
daddr_t sdbase; /* offset in subdisk of stripe base */
int sdcount; /* number of disks involved in this transfer */
daddr_t diskstart; /* remember where this transfer starts */
int psdno; /* number of parity subdisk */
int badsdno; /* number of down subdisk, if there is one */
int firstsdno; /* first data subdisk number */
/* These correspond to the fields in rqelement, sort of */
int useroffset;
/*
* Initial offset and length values for the first
* data block
*/
int initoffset; /* start address of block to transfer */
short initlen; /* length in sectors of data transfer */
/* Define a normal operation */
int dataoffset; /* start address of block to transfer */
int datalen; /* length in sectors of data transfer */
/* Define a group operation */
int groupoffset; /* subdisk offset of group operation */
int grouplen; /* length in sectors of group operation */
/* Define a normal write operation */
int writeoffset; /* subdisk offset of normal write */
int writelen; /* length in sectors of write operation */
enum xferinfo flags; /* to check what we're doing */
int rqcount; /* number of elements in request */
};
enum requeststatus bre5(struct request *rq,
int plexno,
daddr_t * diskstart,
daddr_t diskend);
void complete_raid5_write(struct rqelement *);
enum requeststatus build_rq_buffer(struct rqelement *rqe, struct plex *plex);
void setrqebounds(struct rqelement *rqe, struct metrics *mp);
/*
* define the low-level requests needed to perform
* a high-level I/O operation for a specific plex
* 'plexno'.
*
* Return 0 if all subdisks involved in the
* request are up, 1 if some subdisks are not up,
* and -1 if the request is at least partially
* outside the bounds of the subdisks.
*
* Modify the pointer *diskstart to point to the
* end address. On read, return on the first bad
* subdisk, so that the caller
* (build_read_request) can try alternatives.
*
* On entry to this routine, the prq structures
* are not assigned. The assignment is performed
* by expandrq(). Strictly speaking, the elements
* rqe->sdno of all entries should be set to -1,
* since 0 (from bzero) is a valid subdisk number.
* We avoid this problem by initializing the ones
* we use, and not looking at the others (index >=
* prq->requests).
*/
enum requeststatus
bre5(struct request *rq,
int plexno,
daddr_t * diskaddr,
daddr_t diskend)
{
struct metrics m; /* most of the information */
struct sd *sd;
struct plex *plex;
struct buf *bp; /* user's bp */
struct rqgroup *rqg; /* the request group that we will create */
struct rqelement *rqe; /* point to this request information */
int rsectors; /* sectors remaining in this stripe */
int mysdno; /* another sd index in loops */
int rqno; /* request number */
rqg = NULL; /* shut up, damn compiler */
m.diskstart = *diskaddr; /* start of transfer */
bp = rq->bp; /* buffer pointer */
plex = &PLEX[plexno]; /* point to the plex */
while (*diskaddr < diskend) { /* until we get it all sorted out */
if (*diskaddr >= plex->length) /* beyond the end of the plex */
return REQUEST_EOF; /* can't continue */
m.badsdno = -1; /* no bad subdisk yet */
/* Part A: Define the request */
/*
* First, calculate some sizes:
* The offset of the start address from
* the start of the stripe.
*/
m.stripeoffset = *diskaddr % (plex->stripesize * (plex->subdisks - 1));
/*
* The plex-relative address of the
* start of the stripe.
*/
m.stripebase = *diskaddr - m.stripeoffset;
/* subdisk containing the parity stripe */
if (plex->organization == plex_raid5)
m.psdno = plex->subdisks - 1
- (*diskaddr / (plex->stripesize * (plex->subdisks - 1)))
% plex->subdisks;
else /* RAID-4 */
m.psdno = plex->subdisks - 1;
/*
* The number of the subdisk in which
* the start is located.
*/
m.firstsdno = m.stripeoffset / plex->stripesize;
if (m.firstsdno >= m.psdno) /* at or past parity sd */
m.firstsdno++; /* increment it */
/*
* The offset from the beginning of
* the stripe on this subdisk.
*/
m.initoffset = m.stripeoffset % plex->stripesize;
/* The offset of the stripe start relative to this subdisk */
m.sdbase = m.stripebase / (plex->subdisks - 1);
m.useroffset = *diskaddr - m.diskstart; /* The offset of the start in the user buffer */
/*
* The number of sectors to transfer in the
* current (first) subdisk.
*/
m.initlen = min(diskend - *diskaddr, /* the amount remaining to transfer */
plex->stripesize - m.initoffset); /* and the amount left in this block */
/*
* The number of sectors to transfer in this stripe
* is the minumum of the amount remaining to transfer
* and the amount left in this stripe.
*/
m.stripesectors = min(diskend - *diskaddr,
plex->stripesize * (plex->subdisks - 1) - m.stripeoffset);
/* The number of data subdisks involved in this request */
m.sdcount = (m.stripesectors + m.initoffset + plex->stripesize - 1) / plex->stripesize;
/* Part B: decide what kind of transfer this will be.
* start and end addresses of the transfer in
* the current block.
*
* There are a number of different kinds of
* transfer, each of which relates to a
* specific subdisk:
*
* 1. Normal read. All participating subdisks
* are up, and the transfer can be made
* directly to the user buffer. The bounds
* of the transfer are described by
* m.dataoffset and m.datalen. We have
* already calculated m.initoffset and
* m.initlen, which define the parameters
* for the first data block.
*
* 2. Recovery read. One participating
* subdisk is down. To recover data, all
* the other subdisks, including the parity
* subdisk, must be read. The data is
* recovered by exclusive-oring all the
* other blocks. The bounds of the
* transfer are described by m.groupoffset
* and m.grouplen.
*
* 3. A read request may request reading both
* available data (normal read) and
* non-available data (recovery read).
* This can be a problem if the address
* ranges of the two reads do not coincide:
* in this case, the normal read needs to
* be extended to cover the address range
* of the recovery read, and must thus be
* performed out of malloced memory.
*
* 4. Normal write. All the participating
* subdisks are up. The bounds of the
* transfer are described by m.dataoffset
* and m.datalen. Since these values
* differ for each block, we calculate the
* bounds for the parity block
* independently as the maximum of the
* individual blocks and store these values
* in m.writeoffset and m.writelen. This
* write proceeds in four phases:
*
* i. Read the old contents of each block
* and the parity block.
* ii. ``Remove'' the old contents from
* the parity block with exclusive or.
* iii. ``Insert'' the new contents of the
* block in the parity block, again
* with exclusive or.
*
* iv. Write the new contents of the data
* blocks and the parity block. The data
* block transfers can be made directly from
* the user buffer.
*
* 5. Degraded write where the data block is
* not available. The bounds of the
* transfer are described by m.groupoffset
* and m.grouplen. This requires the
* following steps:
*
* i. Read in all the other data blocks,
* excluding the parity block.
*
* ii. Recreate the parity block from the
* other data blocks and the data to be
* written.
*
* iii. Write the parity block.
*
* 6. Parityless write, a write where the
* parity block is not available. This is
* in fact the simplest: just write the
* data blocks. This can proceed directly
* from the user buffer. The bounds of the
* transfer are described by m.dataoffset
* and m.datalen.
*
* 7. Combination of degraded data block write
* and normal write. In this case the
* address ranges of the reads may also
* need to be extended to cover all
* participating blocks.
*
* All requests in a group transfer transfer
* the same address range relative to their
* subdisk. The individual transfers may
* vary, but since our group of requests is
* all in a single slice, we can define a
* range in which they all fall.
*
* In the following code section, we determine
* which kind of transfer we will perform. If
* there is a group transfer, we also decide
* its bounds relative to the subdisks. At
* the end, we have the following values:
*
* m.flags indicates the kinds of transfers
* we will perform.
* m.initoffset indicates the offset of the
* beginning of any data operation relative
* to the beginning of the stripe base.
* m.initlen specifies the length of any data
* operation.
* m.dataoffset contains the same value as
* m.initoffset.
* m.datalen contains the same value as
* m.initlen. Initially dataoffset and
* datalen describe the parameters for the
* first data block; while building the data
* block requests, they are updated for each
* block.
* m.groupoffset indicates the offset of any
* group operation relative to the beginning
* of the stripe base.
* m.grouplen specifies the length of any
* group operation.
* m.writeoffset indicates the offset of a
* normal write relative to the beginning of
* the stripe base. This value differs from
* m.dataoffset in that it applies to the
* entire operation, and not just the first
* block.
* m.writelen specifies the total span of a
* normal write operation. writeoffset and
* writelen are used to define the parity
* block.
*/
m.groupoffset = 0; /* assume no group... */
m.grouplen = 0; /* until we know we have one */
m.writeoffset = m.initoffset; /* start offset of transfer */
m.writelen = 0; /* nothing to write yet */
m.flags = 0; /* no flags yet */
rsectors = m.stripesectors; /* remaining sectors to examine */
m.dataoffset = m.initoffset; /* start at the beginning of the transfer */
m.datalen = m.initlen;
if (m.sdcount > 1) {
plex->multiblock++; /* more than one block for the request */
/*
* If we have two transfers that don't overlap,
* (one at the end of the first block, the other
* at the beginning of the second block),
* it's cheaper to split them.
*/
if (rsectors < plex->stripesize) {
m.sdcount = 1; /* just one subdisk */
m.stripesectors = m.initlen; /* and just this many sectors */
rsectors = m.initlen; /* and in the loop counter */
}
}
if (SD[plex->sdnos[m.psdno]].state < sd_reborn) /* is our parity subdisk down? */
m.badsdno = m.psdno; /* note that it's down */
if (bp->b_iocmd == BIO_READ) { /* read operation */
for (mysdno = m.firstsdno; rsectors > 0; mysdno++) {
if (mysdno == m.psdno) /* ignore parity on read */
mysdno++;
if (mysdno == plex->subdisks) /* wraparound */
mysdno = 0;
if (mysdno == m.psdno) /* parity, */
mysdno++; /* we've given already */
if (SD[plex->sdnos[mysdno]].state < sd_reborn) { /* got a bad subdisk, */
if (m.badsdno >= 0) /* we had one already, */
return REQUEST_DOWN; /* we can't take a second */
m.badsdno = mysdno; /* got the first */
m.groupoffset = m.dataoffset; /* define the bounds */
m.grouplen = m.datalen;
m.flags |= XFR_RECOVERY_READ; /* we need recovery */
plex->recovered_reads++; /* count another one */
} else
m.flags |= XFR_NORMAL_READ; /* normal read */
/* Update the pointers for the next block */
m.dataoffset = 0; /* back to the start of the stripe */
rsectors -= m.datalen; /* remaining sectors to examine */
m.datalen = min(rsectors, plex->stripesize); /* amount that will fit in this block */
}
} else { /* write operation */
for (mysdno = m.firstsdno; rsectors > 0; mysdno++) {
if (mysdno == m.psdno) /* parity stripe, we've dealt with that */
mysdno++;
if (mysdno == plex->subdisks) /* wraparound */
mysdno = 0;
if (mysdno == m.psdno) /* parity, */
mysdno++; /* we've given already */
sd = &SD[plex->sdnos[mysdno]];
if (sd->state != sd_up) {
enum requeststatus s;
s = checksdstate(sd, rq, *diskaddr, diskend); /* do we need to change state? */
if (s && (m.badsdno >= 0)) { /* second bad disk, */
int sdno;
/*
* If the parity disk is down, there's
* no recovery. We make all involved
* subdisks stale. Otherwise, we
* should be able to recover, but it's
* like pulling teeth. Fix it later.
*/
for (sdno = 0; sdno < m.sdcount; sdno++) {
struct sd *sd = &SD[plex->sdnos[sdno]];
if (sd->state >= sd_reborn) /* sort of up, */
set_sd_state(sd->sdno, sd_stale, setstate_force); /* make it stale */
}
return s; /* and crap out */
}
m.badsdno = mysdno; /* note which one is bad */
m.flags |= XFR_DEGRADED_WRITE; /* we need recovery */
plex->degraded_writes++; /* count another one */
m.groupoffset = m.dataoffset; /* define the bounds */
m.grouplen = m.datalen;
} else {
m.flags |= XFR_NORMAL_WRITE; /* normal write operation */
if (m.writeoffset > m.dataoffset) { /* move write operation lower */
m.writelen = max(m.writeoffset + m.writelen,
m.dataoffset + m.datalen)
- m.dataoffset;
m.writeoffset = m.dataoffset;
} else
m.writelen = max(m.writeoffset + m.writelen,
m.dataoffset + m.datalen)
- m.writeoffset;
}
/* Update the pointers for the next block */
m.dataoffset = 0; /* back to the start of the stripe */
rsectors -= m.datalen; /* remaining sectors to examine */
m.datalen = min(rsectors, plex->stripesize); /* amount that will fit in this block */
}
if (m.badsdno == m.psdno) { /* got a bad parity block, */
struct sd *psd = &SD[plex->sdnos[m.psdno]];
if (psd->state == sd_down)
set_sd_state(psd->sdno, sd_obsolete, setstate_force); /* it's obsolete now */
else if (psd->state == sd_crashed)
set_sd_state(psd->sdno, sd_stale, setstate_force); /* it's stale now */
m.flags &= ~XFR_NORMAL_WRITE; /* this write isn't normal, */
m.flags |= XFR_PARITYLESS_WRITE; /* it's parityless */
plex->parityless_writes++; /* count another one */
}
}
/* reset the initial transfer values */
m.dataoffset = m.initoffset; /* start at the beginning of the transfer */
m.datalen = m.initlen;
/* decide how many requests we need */
if (m.flags & (XFR_RECOVERY_READ | XFR_DEGRADED_WRITE))
/* doing a recovery read or degraded write, */
m.rqcount = plex->subdisks; /* all subdisks */
else if (m.flags & XFR_NORMAL_WRITE) /* normal write, */
m.rqcount = m.sdcount + 1; /* all data blocks and the parity block */
else /* parityless write or normal read */
m.rqcount = m.sdcount; /* just the data blocks */
/* Part C: build the requests */
rqg = allocrqg(rq, m.rqcount); /* get a request group */
if (rqg == NULL) { /* malloc failed */
bp->b_error = ENOMEM;
bp->b_ioflags |= BIO_ERROR;
bufdone(bp);
return REQUEST_ENOMEM;
}
rqg->plexno = plexno;
rqg->flags = m.flags;
rqno = 0; /* index in the request group */
/* 1: PARITY BLOCK */
/*
* Are we performing an operation which requires parity? In that case,
* work out the parameters and define the parity block.
* XFR_PARITYOP is XFR_NORMAL_WRITE | XFR_RECOVERY_READ | XFR_DEGRADED_WRITE
*/
if (m.flags & XFR_PARITYOP) { /* need parity */
rqe = &rqg->rqe[rqno]; /* point to element */
sd = &SD[plex->sdnos[m.psdno]]; /* the subdisk in question */
rqe->rqg = rqg; /* point back to group */
rqe->flags = (m.flags | XFR_PARITY_BLOCK | XFR_MALLOCED) /* always malloc parity block */
&~(XFR_NORMAL_READ | XFR_PARITYLESS_WRITE); /* transfer flags without data op stuf */
setrqebounds(rqe, &m); /* set up the bounds of the transfer */
rqe->sdno = sd->sdno; /* subdisk number */
rqe->driveno = sd->driveno;
if (build_rq_buffer(rqe, plex)) /* build the buffer */
return REQUEST_ENOMEM; /* can't do it */
rqe->b.b_iocmd = BIO_READ; /* we must read first */
m.sdcount++; /* adjust the subdisk count */
rqno++; /* and point to the next request */
}
/*
* 2: DATA BLOCKS
* Now build up requests for the blocks required
* for individual transfers
*/
for (mysdno = m.firstsdno; rqno < m.sdcount; mysdno++, rqno++) {
if (mysdno == m.psdno) /* parity, */
mysdno++; /* we've given already */
if (mysdno == plex->subdisks) /* got to the end, */
mysdno = 0; /* wrap around */
if (mysdno == m.psdno) /* parity, */
mysdno++; /* we've given already */
rqe = &rqg->rqe[rqno]; /* point to element */
sd = &SD[plex->sdnos[mysdno]]; /* the subdisk in question */
rqe->rqg = rqg; /* point to group */
if (m.flags & XFR_NEEDS_MALLOC) /* we need a malloced buffer first */
rqe->flags = m.flags | XFR_DATA_BLOCK | XFR_MALLOCED; /* transfer flags */
else
rqe->flags = m.flags | XFR_DATA_BLOCK; /* transfer flags */
if (mysdno == m.badsdno) { /* this is the bad subdisk */
rqg->badsdno = rqno; /* note which one */
rqe->flags |= XFR_BAD_SUBDISK; /* note that it's dead */
/*
* we can't read or write from/to it,
* but we don't need to malloc
*/
rqe->flags &= ~(XFR_MALLOCED | XFR_NORMAL_READ | XFR_NORMAL_WRITE);
}
setrqebounds(rqe, &m); /* set up the bounds of the transfer */
rqe->useroffset = m.useroffset; /* offset in user buffer */
rqe->sdno = sd->sdno; /* subdisk number */
rqe->driveno = sd->driveno;
if (build_rq_buffer(rqe, plex)) /* build the buffer */
return REQUEST_ENOMEM; /* can't do it */
if ((m.flags & XFR_PARITYOP) /* parity operation, */
&&((m.flags & XFR_BAD_SUBDISK) == 0)) /* and not the bad subdisk, */
rqe->b.b_iocmd = BIO_READ; /* we must read first */
/* Now update pointers for the next block */
*diskaddr += m.datalen; /* skip past what we've done */
m.stripesectors -= m.datalen; /* deduct from what's left */
m.useroffset += m.datalen; /* and move on in the user buffer */
m.datalen = min(m.stripesectors, plex->stripesize); /* and recalculate */
m.dataoffset = 0; /* start at the beginning of next block */
}
/*
* 3: REMAINING BLOCKS FOR RECOVERY
* Finally, if we have a recovery operation, build
* up transfers for the other subdisks. Follow the
* subdisks around until we get to where we started.
* These requests use only the group parameters.
*/
if ((rqno < m.rqcount) /* haven't done them all already */
&&(m.flags & (XFR_RECOVERY_READ | XFR_DEGRADED_WRITE))) {
for (; rqno < m.rqcount; rqno++, mysdno++) {
if (mysdno == m.psdno) /* parity, */
mysdno++; /* we've given already */
if (mysdno == plex->subdisks) /* got to the end, */
mysdno = 0; /* wrap around */
if (mysdno == m.psdno) /* parity, */
mysdno++; /* we've given already */
rqe = &rqg->rqe[rqno]; /* point to element */
sd = &SD[plex->sdnos[mysdno]]; /* the subdisk in question */
rqe->rqg = rqg; /* point to group */
rqe->sdoffset = m.sdbase + m.groupoffset; /* start of transfer */
rqe->dataoffset = 0; /* for tidiness' sake */
rqe->groupoffset = 0; /* group starts at the beginining */
rqe->datalen = 0;
rqe->grouplen = m.grouplen;
rqe->buflen = m.grouplen;
rqe->flags = (m.flags | XFR_MALLOCED) /* transfer flags without data op stuf */
&~XFR_DATAOP;
rqe->sdno = sd->sdno; /* subdisk number */
rqe->driveno = sd->driveno;
if (build_rq_buffer(rqe, plex)) /* build the buffer */
return REQUEST_ENOMEM; /* can't do it */
rqe->b.b_iocmd = BIO_READ; /* we must read first */
}
}
/*
* We need to lock the address range before
* doing anything. We don't have to be
* performing a recovery operation: somebody
* else could be doing so, and the results could
* influence us. Note the fact here, we'll perform
* the lock in launch_requests.
*/
rqg->lockbase = m.stripebase;
if (*diskaddr < diskend) /* didn't finish the request on this stripe */
plex->multistripe++; /* count another one */
}
return REQUEST_OK;
}
/*
* Helper function for rqe5: adjust the bounds of
* the transfers to minimize the buffer
* allocation.
*
* Each request can handle two of three different
* data ranges:
*
* 1. The range described by the parameters
* dataoffset and datalen, for normal read or
* parityless write.
* 2. The range described by the parameters
* groupoffset and grouplen, for recovery read
* and degraded write.
* 3. For normal write, the range depends on the
* kind of block. For data blocks, the range
* is defined by dataoffset and datalen. For
* parity blocks, it is defined by writeoffset
* and writelen.
*
* In order not to allocate more memory than
* necessary, this function adjusts the bounds
* parameter for each request to cover just the
* minimum necessary for the function it performs.
* This will normally vary from one request to the
* next.
*
* Things are slightly different for the parity
* block. In this case, the bounds defined by
* mp->writeoffset and mp->writelen also play a
* r<>le. Select this case by setting the
* parameter forparity != 0
*/
void
setrqebounds(struct rqelement *rqe, struct metrics *mp)
{
/* parity block of a normal write */
if ((rqe->flags & (XFR_NORMAL_WRITE | XFR_PARITY_BLOCK))
== (XFR_NORMAL_WRITE | XFR_PARITY_BLOCK)) { /* case 3 */
if (rqe->flags & XFR_DEGRADED_WRITE) { /* also degraded write */
/*
* With a combined normal and degraded write, we
* will zero out the area of the degraded write
* in the second phase, so we don't need to read
* it in. Unfortunately, we need a way to tell
* build_request_buffer the size of the buffer,
* and currently that's the length of the read.
* As a result, we read everything, even the stuff
* that we're going to nuke.
* FIXME XXX
*/
if (mp->groupoffset < mp->writeoffset) { /* group operation starts lower */
rqe->sdoffset = mp->sdbase + mp->groupoffset; /* start of transfer */
rqe->dataoffset = mp->writeoffset - mp->groupoffset; /* data starts here */
rqe->groupoffset = 0; /* and the group at the beginning */
} else { /* individual data starts first */
rqe->sdoffset = mp->sdbase + mp->writeoffset; /* start of transfer */
rqe->dataoffset = 0; /* individual data starts at the beginning */
rqe->groupoffset = mp->groupoffset - mp->writeoffset; /* group starts here */
}
rqe->datalen = mp->writelen;
rqe->grouplen = mp->grouplen;
} else { /* just normal write (case 3) */
rqe->sdoffset = mp->sdbase + mp->writeoffset; /* start of transfer */
rqe->dataoffset = 0; /* degradation starts at the beginning */
rqe->groupoffset = 0; /* for tidiness' sake */
rqe->datalen = mp->writelen;
rqe->grouplen = 0;
}
} else if (rqe->flags & XFR_DATAOP) { /* data operation (case 1 or 3) */
if (rqe->flags & XFR_GROUPOP) { /* also a group operation (case 2) */
if (mp->groupoffset < mp->dataoffset) { /* group operation starts lower */
rqe->sdoffset = mp->sdbase + mp->groupoffset; /* start of transfer */
rqe->dataoffset = mp->dataoffset - mp->groupoffset; /* data starts here */
rqe->groupoffset = 0; /* and the group at the beginning */
} else { /* individual data starts first */
rqe->sdoffset = mp->sdbase + mp->dataoffset; /* start of transfer */
rqe->dataoffset = 0; /* individual data starts at the beginning */
rqe->groupoffset = mp->groupoffset - mp->dataoffset; /* group starts here */
}
rqe->datalen = mp->datalen;
rqe->grouplen = mp->grouplen;
} else { /* just data operation (case 1) */
rqe->sdoffset = mp->sdbase + mp->dataoffset; /* start of transfer */
rqe->dataoffset = 0; /* degradation starts at the beginning */
rqe->groupoffset = 0; /* for tidiness' sake */
rqe->datalen = mp->datalen;
rqe->grouplen = 0;
}
} else { /* just group operations (case 2) */
rqe->sdoffset = mp->sdbase + mp->groupoffset; /* start of transfer */
rqe->dataoffset = 0; /* for tidiness' sake */
rqe->groupoffset = 0; /* group starts at the beginining */
rqe->datalen = 0;
rqe->grouplen = mp->grouplen;
}
rqe->buflen = max(rqe->dataoffset + rqe->datalen, /* total buffer length */
rqe->groupoffset + rqe->grouplen);
}
/* Local Variables: */
/* fill-column: 50 */
/* End: */
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