subr_sglist.c

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    1 /*-
    2  * Copyright (c) 2008 Yahoo!, Inc.
    3  * All rights reserved.
    4  * Written by: John Baldwin <jhb@FreeBSD.org>
    5  *
    6  * Redistribution and use in source and binary forms, with or without
    7  * modification, are permitted provided that the following conditions
    8  * are met:
    9  * 1. Redistributions of source code must retain the above copyright
   10  *    notice, this list of conditions and the following disclaimer.
   11  * 2. Redistributions in binary form must reproduce the above copyright
   12  *    notice, this list of conditions and the following disclaimer in the
   13  *    documentation and/or other materials provided with the distribution.
   14  * 3. Neither the name of the author nor the names of any co-contributors
   15  *    may be used to endorse or promote products derived from this software
   16  *    without specific prior written permission.
   17  *
   18  * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
   19  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
   20  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
   21  * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
   22  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
   23  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
   24  * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
   25  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
   26  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
   27  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
   28  * SUCH DAMAGE.
   29  */
   30 
   31 #include <sys/cdefs.h>
   32 __FBSDID("$FreeBSD: releng/11.1/sys/kern/subr_sglist.c 300337 2016-05-20 23:28:43Z jhb $");
   33 
   34 #include <sys/param.h>
   35 #include <sys/kernel.h>
   36 #include <sys/bio.h>
   37 #include <sys/malloc.h>
   38 #include <sys/mbuf.h>
   39 #include <sys/proc.h>
   40 #include <sys/sglist.h>
   41 #include <sys/uio.h>
   42 
   43 #include <vm/vm.h>
   44 #include <vm/vm_page.h>
   45 #include <vm/pmap.h>
   46 #include <vm/vm_map.h>
   47 
   48 #include <sys/ktr.h>
   49 
   50 static MALLOC_DEFINE(M_SGLIST, "sglist", "scatter/gather lists");
   51 
   52 /*
   53  * Convenience macros to save the state of an sglist so it can be restored
   54  * if an append attempt fails.  Since sglist's only grow we only need to
   55  * save the current count of segments and the length of the ending segment.
   56  * Earlier segments will not be changed by an append, and the only change
   57  * that can occur to the ending segment is that it can be extended.
   58  */
   59 struct sgsave {
   60         u_short sg_nseg;
   61         size_t ss_len;
   62 };
   63 
   64 #define SGLIST_SAVE(sg, sgsave) do {                                    \
   65         (sgsave).sg_nseg = (sg)->sg_nseg;                               \
   66         if ((sgsave).sg_nseg > 0)                                       \
   67                 (sgsave).ss_len = (sg)->sg_segs[(sgsave).sg_nseg - 1].ss_len; \
   68         else                                                            \
   69                 (sgsave).ss_len = 0;                                    \
   70 } while (0)
   71 
   72 #define SGLIST_RESTORE(sg, sgsave) do {                                 \
   73         (sg)->sg_nseg = (sgsave).sg_nseg;                               \
   74         if ((sgsave).sg_nseg > 0)                                       \
   75                 (sg)->sg_segs[(sgsave).sg_nseg - 1].ss_len = (sgsave).ss_len; \
   76 } while (0)
   77 
   78 /*
   79  * Append a single (paddr, len) to a sglist.  sg is the list and ss is
   80  * the current segment in the list.  If we run out of segments then
   81  * EFBIG will be returned.
   82  */
   83 static __inline int
   84 _sglist_append_range(struct sglist *sg, struct sglist_seg **ssp,
   85     vm_paddr_t paddr, size_t len)
   86 {
   87         struct sglist_seg *ss;
   88 
   89         ss = *ssp;
   90         if (ss->ss_paddr + ss->ss_len == paddr)
   91                 ss->ss_len += len;
   92         else {
   93                 if (sg->sg_nseg == sg->sg_maxseg)
   94                         return (EFBIG);
   95                 ss++;
   96                 ss->ss_paddr = paddr;
   97                 ss->ss_len = len;
   98                 sg->sg_nseg++;
   99                 *ssp = ss;
  100         }
  101         return (0);
  102 }
  103 
  104 /*
  105  * Worker routine to append a virtual address range (either kernel or
  106  * user) to a scatter/gather list.
  107  */
  108 static __inline int
  109 _sglist_append_buf(struct sglist *sg, void *buf, size_t len, pmap_t pmap,
  110     size_t *donep)
  111 {
  112         struct sglist_seg *ss;
  113         vm_offset_t vaddr, offset;
  114         vm_paddr_t paddr;
  115         size_t seglen;
  116         int error;
  117 
  118         if (donep)
  119                 *donep = 0;
  120         if (len == 0)
  121                 return (0);
  122 
  123         /* Do the first page.  It may have an offset. */
  124         vaddr = (vm_offset_t)buf;
  125         offset = vaddr & PAGE_MASK;
  126         if (pmap != NULL)
  127                 paddr = pmap_extract(pmap, vaddr);
  128         else
  129                 paddr = pmap_kextract(vaddr);
  130         seglen = MIN(len, PAGE_SIZE - offset);
  131         if (sg->sg_nseg == 0) {
  132                 ss = sg->sg_segs;
  133                 ss->ss_paddr = paddr;
  134                 ss->ss_len = seglen;
  135                 sg->sg_nseg = 1;
  136         } else {
  137                 ss = &sg->sg_segs[sg->sg_nseg - 1];
  138                 error = _sglist_append_range(sg, &ss, paddr, seglen);
  139                 if (error)
  140                         return (error);
  141         }
  142         vaddr += seglen;
  143         len -= seglen;
  144         if (donep)
  145                 *donep += seglen;
  146 
  147         while (len > 0) {
  148                 seglen = MIN(len, PAGE_SIZE);
  149                 if (pmap != NULL)
  150                         paddr = pmap_extract(pmap, vaddr);
  151                 else
  152                         paddr = pmap_kextract(vaddr);
  153                 error = _sglist_append_range(sg, &ss, paddr, seglen);
  154                 if (error)
  155                         return (error);
  156                 vaddr += seglen;
  157                 len -= seglen;
  158                 if (donep)
  159                         *donep += seglen;
  160         }
  161 
  162         return (0);
  163 }
  164 
  165 /*
  166  * Determine the number of scatter/gather list elements needed to
  167  * describe a kernel virtual address range.
  168  */
  169 int
  170 sglist_count(void *buf, size_t len)
  171 {
  172         vm_offset_t vaddr, vendaddr;
  173         vm_paddr_t lastaddr, paddr;
  174         int nsegs;
  175 
  176         if (len == 0)
  177                 return (0);
  178 
  179         vaddr = trunc_page((vm_offset_t)buf);
  180         vendaddr = (vm_offset_t)buf + len;
  181         nsegs = 1;
  182         lastaddr = pmap_kextract(vaddr);
  183         vaddr += PAGE_SIZE;
  184         while (vaddr < vendaddr) {
  185                 paddr = pmap_kextract(vaddr);
  186                 if (lastaddr + PAGE_SIZE != paddr)
  187                         nsegs++;
  188                 lastaddr = paddr;
  189                 vaddr += PAGE_SIZE;
  190         }
  191         return (nsegs);
  192 }
  193 
  194 /*
  195  * Determine the number of scatter/gather list elements needed to
  196  * describe a buffer backed by an array of VM pages.
  197  */
  198 int
  199 sglist_count_vmpages(vm_page_t *m, size_t pgoff, size_t len)
  200 {
  201         vm_paddr_t lastaddr, paddr;
  202         int i, nsegs;
  203 
  204         if (len == 0)
  205                 return (0);
  206 
  207         len += pgoff;
  208         nsegs = 1;
  209         lastaddr = VM_PAGE_TO_PHYS(m[0]);
  210         for (i = 1; len > PAGE_SIZE; len -= PAGE_SIZE, i++) {
  211                 paddr = VM_PAGE_TO_PHYS(m[i]);
  212                 if (lastaddr + PAGE_SIZE != paddr)
  213                         nsegs++;
  214                 lastaddr = paddr;
  215         }
  216         return (nsegs);
  217 }
  218 
  219 /*
  220  * Allocate a scatter/gather list along with 'nsegs' segments.  The
  221  * 'mflags' parameters are the same as passed to malloc(9).  The caller
  222  * should use sglist_free() to free this list.
  223  */
  224 struct sglist *
  225 sglist_alloc(int nsegs, int mflags)
  226 {
  227         struct sglist *sg;
  228 
  229         sg = malloc(sizeof(struct sglist) + nsegs * sizeof(struct sglist_seg),
  230             M_SGLIST, mflags);
  231         if (sg == NULL)
  232                 return (NULL);
  233         sglist_init(sg, nsegs, (struct sglist_seg *)(sg + 1));
  234         return (sg);
  235 }
  236 
  237 /*
  238  * Free a scatter/gather list allocated via sglist_allc().
  239  */
  240 void
  241 sglist_free(struct sglist *sg)
  242 {
  243 
  244         if (sg == NULL)
  245                 return;
  246 
  247         if (refcount_release(&sg->sg_refs))
  248                 free(sg, M_SGLIST);
  249 }
  250 
  251 /*
  252  * Append the segments to describe a single kernel virtual address
  253  * range to a scatter/gather list.  If there are insufficient
  254  * segments, then this fails with EFBIG.
  255  */
  256 int
  257 sglist_append(struct sglist *sg, void *buf, size_t len)
  258 {
  259         struct sgsave save;
  260         int error;
  261 
  262         if (sg->sg_maxseg == 0)
  263                 return (EINVAL);
  264         SGLIST_SAVE(sg, save);
  265         error = _sglist_append_buf(sg, buf, len, NULL, NULL);
  266         if (error)
  267                 SGLIST_RESTORE(sg, save);
  268         return (error);
  269 }
  270 
  271 /*
  272  * Append the segments to describe a bio's data to a scatter/gather list.
  273  * If there are insufficient segments, then this fails with EFBIG.
  274  *
  275  * NOTE: This function expects bio_bcount to be initialized.
  276  */
  277 int
  278 sglist_append_bio(struct sglist *sg, struct bio *bp)
  279 {
  280         int error;
  281 
  282         if ((bp->bio_flags & BIO_UNMAPPED) == 0)
  283                 error = sglist_append(sg, bp->bio_data, bp->bio_bcount);
  284         else
  285                 error = sglist_append_vmpages(sg, bp->bio_ma,
  286                     bp->bio_ma_offset, bp->bio_bcount);
  287         return (error);
  288 }
  289 
  290 /*
  291  * Append a single physical address range to a scatter/gather list.
  292  * If there are insufficient segments, then this fails with EFBIG.
  293  */
  294 int
  295 sglist_append_phys(struct sglist *sg, vm_paddr_t paddr, size_t len)
  296 {
  297         struct sglist_seg *ss;
  298         struct sgsave save;
  299         int error;
  300 
  301         if (sg->sg_maxseg == 0)
  302                 return (EINVAL);
  303         if (len == 0)
  304                 return (0);
  305 
  306         if (sg->sg_nseg == 0) {
  307                 sg->sg_segs[0].ss_paddr = paddr;
  308                 sg->sg_segs[0].ss_len = len;
  309                 sg->sg_nseg = 1;
  310                 return (0);
  311         }
  312         ss = &sg->sg_segs[sg->sg_nseg - 1];
  313         SGLIST_SAVE(sg, save);
  314         error = _sglist_append_range(sg, &ss, paddr, len);
  315         if (error)
  316                 SGLIST_RESTORE(sg, save);
  317         return (error);
  318 }
  319 
  320 /*
  321  * Append the segments that describe a single mbuf chain to a
  322  * scatter/gather list.  If there are insufficient segments, then this
  323  * fails with EFBIG.
  324  */
  325 int
  326 sglist_append_mbuf(struct sglist *sg, struct mbuf *m0)
  327 {
  328         struct sgsave save;
  329         struct mbuf *m;
  330         int error;
  331 
  332         if (sg->sg_maxseg == 0)
  333                 return (EINVAL);
  334 
  335         error = 0;
  336         SGLIST_SAVE(sg, save);
  337         for (m = m0; m != NULL; m = m->m_next) {
  338                 if (m->m_len > 0) {
  339                         error = sglist_append(sg, m->m_data, m->m_len);
  340                         if (error) {
  341                                 SGLIST_RESTORE(sg, save);
  342                                 return (error);
  343                         }
  344                 }
  345         }
  346         return (0);
  347 }
  348 
  349 /*
  350  * Append the segments that describe a buffer spanning an array of VM
  351  * pages.  The buffer begins at an offset of 'pgoff' in the first
  352  * page.
  353  */
  354 int
  355 sglist_append_vmpages(struct sglist *sg, vm_page_t *m, size_t pgoff,
  356     size_t len)
  357 {
  358         struct sgsave save;
  359         struct sglist_seg *ss;
  360         vm_paddr_t paddr;
  361         size_t seglen;
  362         int error, i;
  363 
  364         if (sg->sg_maxseg == 0)
  365                 return (EINVAL);
  366         if (len == 0)
  367                 return (0);
  368 
  369         SGLIST_SAVE(sg, save);
  370         i = 0;
  371         if (sg->sg_nseg == 0) {
  372                 seglen = min(PAGE_SIZE - pgoff, len);
  373                 sg->sg_segs[0].ss_paddr = VM_PAGE_TO_PHYS(m[0]) + pgoff;
  374                 sg->sg_segs[0].ss_len = seglen;
  375                 sg->sg_nseg = 1;
  376                 pgoff = 0;
  377                 len -= seglen;
  378                 i++;
  379         }
  380         ss = &sg->sg_segs[sg->sg_nseg - 1];
  381         for (; len > 0; i++, len -= seglen) {
  382                 seglen = min(PAGE_SIZE - pgoff, len);
  383                 paddr = VM_PAGE_TO_PHYS(m[i]) + pgoff;
  384                 error = _sglist_append_range(sg, &ss, paddr, seglen);
  385                 if (error) {
  386                         SGLIST_RESTORE(sg, save);
  387                         return (error);
  388                 }
  389                 pgoff = 0;
  390         }
  391         return (0);
  392 }
  393 
  394 /*
  395  * Append the segments that describe a single user address range to a
  396  * scatter/gather list.  If there are insufficient segments, then this
  397  * fails with EFBIG.
  398  */
  399 int
  400 sglist_append_user(struct sglist *sg, void *buf, size_t len, struct thread *td)
  401 {
  402         struct sgsave save;
  403         int error;
  404 
  405         if (sg->sg_maxseg == 0)
  406                 return (EINVAL);
  407         SGLIST_SAVE(sg, save);
  408         error = _sglist_append_buf(sg, buf, len,
  409             vmspace_pmap(td->td_proc->p_vmspace), NULL);
  410         if (error)
  411                 SGLIST_RESTORE(sg, save);
  412         return (error);
  413 }
  414 
  415 /*
  416  * Append the segments that describe a single uio to a scatter/gather
  417  * list.  If there are insufficient segments, then this fails with
  418  * EFBIG.
  419  */
  420 int
  421 sglist_append_uio(struct sglist *sg, struct uio *uio)
  422 {
  423         struct iovec *iov;
  424         struct sgsave save;
  425         size_t resid, minlen;
  426         pmap_t pmap;
  427         int error, i;
  428 
  429         if (sg->sg_maxseg == 0)
  430                 return (EINVAL);
  431 
  432         resid = uio->uio_resid;
  433         iov = uio->uio_iov;
  434 
  435         if (uio->uio_segflg == UIO_USERSPACE) {
  436                 KASSERT(uio->uio_td != NULL,
  437                     ("sglist_append_uio: USERSPACE but no thread"));
  438                 pmap = vmspace_pmap(uio->uio_td->td_proc->p_vmspace);
  439         } else
  440                 pmap = NULL;
  441 
  442         error = 0;
  443         SGLIST_SAVE(sg, save);
  444         for (i = 0; i < uio->uio_iovcnt && resid != 0; i++) {
  445                 /*
  446                  * Now at the first iovec to load.  Load each iovec
  447                  * until we have exhausted the residual count.
  448                  */
  449                 minlen = MIN(resid, iov[i].iov_len);
  450                 if (minlen > 0) {
  451                         error = _sglist_append_buf(sg, iov[i].iov_base, minlen,
  452                             pmap, NULL);
  453                         if (error) {
  454                                 SGLIST_RESTORE(sg, save);
  455                                 return (error);
  456                         }
  457                         resid -= minlen;
  458                 }
  459         }
  460         return (0);
  461 }
  462 
  463 /*
  464  * Append the segments that describe at most 'resid' bytes from a
  465  * single uio to a scatter/gather list.  If there are insufficient
  466  * segments, then only the amount that fits is appended.
  467  */
  468 int
  469 sglist_consume_uio(struct sglist *sg, struct uio *uio, size_t resid)
  470 {
  471         struct iovec *iov;
  472         size_t done;
  473         pmap_t pmap;
  474         int error, len;
  475 
  476         if (sg->sg_maxseg == 0)
  477                 return (EINVAL);
  478 
  479         if (uio->uio_segflg == UIO_USERSPACE) {
  480                 KASSERT(uio->uio_td != NULL,
  481                     ("sglist_consume_uio: USERSPACE but no thread"));
  482                 pmap = vmspace_pmap(uio->uio_td->td_proc->p_vmspace);
  483         } else
  484                 pmap = NULL;
  485 
  486         error = 0;
  487         while (resid > 0 && uio->uio_resid) {
  488                 iov = uio->uio_iov;
  489                 len = iov->iov_len;
  490                 if (len == 0) {
  491                         uio->uio_iov++;
  492                         uio->uio_iovcnt--;
  493                         continue;
  494                 }
  495                 if (len > resid)
  496                         len = resid;
  497 
  498                 /*
  499                  * Try to append this iovec.  If we run out of room,
  500                  * then break out of the loop.
  501                  */
  502                 error = _sglist_append_buf(sg, iov->iov_base, len, pmap, &done);
  503                 iov->iov_base = (char *)iov->iov_base + done;
  504                 iov->iov_len -= done;
  505                 uio->uio_resid -= done;
  506                 uio->uio_offset += done;
  507                 resid -= done;
  508                 if (error)
  509                         break;
  510         }
  511         return (0);
  512 }
  513 
  514 /*
  515  * Allocate and populate a scatter/gather list to describe a single
  516  * kernel virtual address range.
  517  */
  518 struct sglist *
  519 sglist_build(void *buf, size_t len, int mflags)
  520 {
  521         struct sglist *sg;
  522         int nsegs;
  523 
  524         if (len == 0)
  525                 return (NULL);
  526 
  527         nsegs = sglist_count(buf, len);
  528         sg = sglist_alloc(nsegs, mflags);
  529         if (sg == NULL)
  530                 return (NULL);
  531         if (sglist_append(sg, buf, len) != 0) {
  532                 sglist_free(sg);
  533                 return (NULL);
  534         }
  535         return (sg);
  536 }
  537 
  538 /*
  539  * Clone a new copy of a scatter/gather list.
  540  */
  541 struct sglist *
  542 sglist_clone(struct sglist *sg, int mflags)
  543 {
  544         struct sglist *new;
  545 
  546         if (sg == NULL)
  547                 return (NULL);
  548         new = sglist_alloc(sg->sg_maxseg, mflags);
  549         if (new == NULL)
  550                 return (NULL);
  551         new->sg_nseg = sg->sg_nseg;
  552         bcopy(sg->sg_segs, new->sg_segs, sizeof(struct sglist_seg) *
  553             sg->sg_nseg);
  554         return (new);
  555 }
  556 
  557 /*
  558  * Calculate the total length of the segments described in a
  559  * scatter/gather list.
  560  */
  561 size_t
  562 sglist_length(struct sglist *sg)
  563 {
  564         size_t space;
  565         int i;
  566 
  567         space = 0;
  568         for (i = 0; i < sg->sg_nseg; i++)
  569                 space += sg->sg_segs[i].ss_len;
  570         return (space);
  571 }
  572 
  573 /*
  574  * Split a scatter/gather list into two lists.  The scatter/gather
  575  * entries for the first 'length' bytes of the 'original' list are
  576  * stored in the '*head' list and are removed from 'original'.
  577  *
  578  * If '*head' is NULL, then a new list will be allocated using
  579  * 'mflags'.  If M_NOWAIT is specified and the allocation fails,
  580  * ENOMEM will be returned.
  581  *
  582  * If '*head' is not NULL, it should point to an empty sglist.  If it
  583  * does not have enough room for the remaining space, then EFBIG will
  584  * be returned.  If '*head' is not empty, then EINVAL will be
  585  * returned.
  586  *
  587  * If 'original' is shared (refcount > 1), then EDOOFUS will be
  588  * returned.
  589  */
  590 int
  591 sglist_split(struct sglist *original, struct sglist **head, size_t length,
  592     int mflags)
  593 {
  594         struct sglist *sg;
  595         size_t space, split;
  596         int count, i;
  597 
  598         if (original->sg_refs > 1)
  599                 return (EDOOFUS);
  600 
  601         /* Figure out how big of a sglist '*head' has to hold. */
  602         count = 0;
  603         space = 0;
  604         split = 0;
  605         for (i = 0; i < original->sg_nseg; i++) {
  606                 space += original->sg_segs[i].ss_len;
  607                 count++;
  608                 if (space >= length) {
  609                         /*
  610                          * If 'length' falls in the middle of a
  611                          * scatter/gather list entry, then 'split'
  612                          * holds how much of that entry will remain in
  613                          * 'original'.
  614                          */
  615                         split = space - length;
  616                         break;
  617                 }
  618         }
  619 
  620         /* Nothing to do, so leave head empty. */
  621         if (count == 0)
  622                 return (0);
  623 
  624         if (*head == NULL) {
  625                 sg = sglist_alloc(count, mflags);
  626                 if (sg == NULL)
  627                         return (ENOMEM);
  628                 *head = sg;
  629         } else {
  630                 sg = *head;
  631                 if (sg->sg_maxseg < count)
  632                         return (EFBIG);
  633                 if (sg->sg_nseg != 0)
  634                         return (EINVAL);
  635         }
  636 
  637         /* Copy 'count' entries to 'sg' from 'original'. */
  638         bcopy(original->sg_segs, sg->sg_segs, count *
  639             sizeof(struct sglist_seg));
  640         sg->sg_nseg = count;
  641 
  642         /*
  643          * If we had to split a list entry, fixup the last entry in
  644          * 'sg' and the new first entry in 'original'.  We also
  645          * decrement 'count' by 1 since we will only be removing
  646          * 'count - 1' segments from 'original' now.
  647          */
  648         if (split != 0) {
  649                 count--;
  650                 sg->sg_segs[count].ss_len -= split;
  651                 original->sg_segs[count].ss_paddr =
  652                     sg->sg_segs[count].ss_paddr + split;
  653                 original->sg_segs[count].ss_len = split;
  654         }
  655 
  656         /* Trim 'count' entries from the front of 'original'. */
  657         original->sg_nseg -= count;
  658         bcopy(original->sg_segs + count, original->sg_segs, count *
  659             sizeof(struct sglist_seg));
  660         return (0);
  661 }
  662 
  663 /*
  664  * Append the scatter/gather list elements in 'second' to the
  665  * scatter/gather list 'first'.  If there is not enough space in
  666  * 'first', EFBIG is returned.
  667  */
  668 int
  669 sglist_join(struct sglist *first, struct sglist *second)
  670 {
  671         struct sglist_seg *flast, *sfirst;
  672         int append;
  673 
  674         /* If 'second' is empty, there is nothing to do. */
  675         if (second->sg_nseg == 0)
  676                 return (0);
  677 
  678         /*
  679          * If the first entry in 'second' can be appended to the last entry
  680          * in 'first' then set append to '1'.
  681          */
  682         append = 0;
  683         flast = &first->sg_segs[first->sg_nseg - 1];
  684         sfirst = &second->sg_segs[0];
  685         if (first->sg_nseg != 0 &&
  686             flast->ss_paddr + flast->ss_len == sfirst->ss_paddr)
  687                 append = 1;
  688 
  689         /* Make sure 'first' has enough room. */
  690         if (first->sg_nseg + second->sg_nseg - append > first->sg_maxseg)
  691                 return (EFBIG);
  692 
  693         /* Merge last in 'first' and first in 'second' if needed. */
  694         if (append)
  695                 flast->ss_len += sfirst->ss_len;
  696 
  697         /* Append new segments from 'second' to 'first'. */
  698         bcopy(first->sg_segs + first->sg_nseg, second->sg_segs + append,
  699             (second->sg_nseg - append) * sizeof(struct sglist_seg));
  700         first->sg_nseg += second->sg_nseg - append;
  701         sglist_reset(second);
  702         return (0);
  703 }
  704 
  705 /*
  706  * Generate a new scatter/gather list from a range of an existing
  707  * scatter/gather list.  The 'offset' and 'length' parameters specify
  708  * the logical range of the 'original' list to extract.  If that range
  709  * is not a subset of the length of 'original', then EINVAL is
  710  * returned.  The new scatter/gather list is stored in '*slice'.
  711  *
  712  * If '*slice' is NULL, then a new list will be allocated using
  713  * 'mflags'.  If M_NOWAIT is specified and the allocation fails,
  714  * ENOMEM will be returned.
  715  *
  716  * If '*slice' is not NULL, it should point to an empty sglist.  If it
  717  * does not have enough room for the remaining space, then EFBIG will
  718  * be returned.  If '*slice' is not empty, then EINVAL will be
  719  * returned.
  720  */
  721 int
  722 sglist_slice(struct sglist *original, struct sglist **slice, size_t offset,
  723     size_t length, int mflags)
  724 {
  725         struct sglist *sg;
  726         size_t space, end, foffs, loffs;
  727         int count, i, fseg;
  728 
  729         /* Nothing to do. */
  730         if (length == 0)
  731                 return (0);
  732 
  733         /* Figure out how many segments '*slice' needs to have. */
  734         end = offset + length;
  735         space = 0;
  736         count = 0;
  737         fseg = 0;
  738         foffs = loffs = 0;
  739         for (i = 0; i < original->sg_nseg; i++) {
  740                 space += original->sg_segs[i].ss_len;
  741                 if (space > offset) {
  742                         /*
  743                          * When we hit the first segment, store its index
  744                          * in 'fseg' and the offset into the first segment
  745                          * of 'offset' in 'foffs'.
  746                          */
  747                         if (count == 0) {
  748                                 fseg = i;
  749                                 foffs = offset - (space -
  750                                     original->sg_segs[i].ss_len);
  751                                 CTR1(KTR_DEV, "sglist_slice: foffs = %08lx",
  752                                     foffs);
  753                         }
  754                         count++;
  755 
  756                         /*
  757                          * When we hit the last segment, break out of
  758                          * the loop.  Store the amount of extra space
  759                          * at the end of this segment in 'loffs'.
  760                          */
  761                         if (space >= end) {
  762                                 loffs = space - end;
  763                                 CTR1(KTR_DEV, "sglist_slice: loffs = %08lx",
  764                                     loffs);
  765                                 break;
  766                         }
  767                 }
  768         }
  769 
  770         /* If we never hit 'end', then 'length' ran off the end, so fail. */
  771         if (space < end)
  772                 return (EINVAL);
  773 
  774         if (*slice == NULL) {
  775                 sg = sglist_alloc(count, mflags);
  776                 if (sg == NULL)
  777                         return (ENOMEM);
  778                 *slice = sg;
  779         } else {
  780                 sg = *slice;
  781                 if (sg->sg_maxseg < count)
  782                         return (EFBIG);
  783                 if (sg->sg_nseg != 0)
  784                         return (EINVAL);
  785         }
  786 
  787         /*
  788          * Copy over 'count' segments from 'original' starting at
  789          * 'fseg' to 'sg'.
  790          */
  791         bcopy(original->sg_segs + fseg, sg->sg_segs,
  792             count * sizeof(struct sglist_seg));
  793         sg->sg_nseg = count;
  794 
  795         /* Fixup first and last segments if needed. */
  796         if (foffs != 0) {
  797                 sg->sg_segs[0].ss_paddr += foffs;
  798                 sg->sg_segs[0].ss_len -= foffs;
  799                 CTR2(KTR_DEV, "sglist_slice seg[0]: %08lx:%08lx",
  800                     (long)sg->sg_segs[0].ss_paddr, sg->sg_segs[0].ss_len);
  801         }
  802         if (loffs != 0) {
  803                 sg->sg_segs[count - 1].ss_len -= loffs;
  804                 CTR2(KTR_DEV, "sglist_slice seg[%d]: len %08x", count - 1,
  805                     sg->sg_segs[count - 1].ss_len);
  806         }
  807         return (0);
  808 }
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FreeBSD/Linux Kernel Cross Reference sys/kern/subr_sglist.c

FreeBSD/Linux Kernel Cross Reference
sys/kern/subr_sglist.c
