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("$FreeBSD$"); 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 * Allocate a scatter/gather list along with 'nsegs' segments. The 196 * 'mflags' parameters are the same as passed to malloc(9). The caller 197 * should use sglist_free() to free this list. 198 */ 199 struct sglist * 200 sglist_alloc(int nsegs, int mflags) 201 { 202 struct sglist *sg; 203 204 sg = malloc(sizeof(struct sglist) + nsegs * sizeof(struct sglist_seg), 205 M_SGLIST, mflags); 206 if (sg == NULL) 207 return (NULL); 208 sglist_init(sg, nsegs, (struct sglist_seg *)(sg + 1)); 209 return (sg); 210 } 211 212 /* 213 * Free a scatter/gather list allocated via sglist_allc(). 214 */ 215 void 216 sglist_free(struct sglist *sg) 217 { 218 219 if (refcount_release(&sg->sg_refs)) 220 free(sg, M_SGLIST); 221 } 222 223 /* 224 * Append the segments to describe a single kernel virtual address 225 * range to a scatter/gather list. If there are insufficient 226 * segments, then this fails with EFBIG. 227 */ 228 int 229 sglist_append(struct sglist *sg, void *buf, size_t len) 230 { 231 struct sgsave save; 232 int error; 233 234 if (sg->sg_maxseg == 0) 235 return (EINVAL); 236 SGLIST_SAVE(sg, save); 237 error = _sglist_append_buf(sg, buf, len, NULL, NULL); 238 if (error) 239 SGLIST_RESTORE(sg, save); 240 return (error); 241 } 242 243 /* 244 * Append the segments to describe a bio's data to a scatter/gather list. 245 * If there are insufficient segments, then this fails with EFBIG. 246 * 247 * NOTE: This function expects bio_bcount to be initialized. 248 */ 249 int 250 sglist_append_bio(struct sglist *sg, struct bio *bp) 251 { 252 struct sgsave save; 253 vm_paddr_t paddr; 254 size_t len, tlen; 255 int error, i, ma_offs; 256 257 if ((bp->bio_flags & BIO_UNMAPPED) == 0) { 258 error = sglist_append(sg, bp->bio_data, bp->bio_bcount); 259 return (error); 260 } 261 262 if (sg->sg_maxseg == 0) 263 return (EINVAL); 264 265 SGLIST_SAVE(sg, save); 266 tlen = bp->bio_bcount; 267 ma_offs = bp->bio_ma_offset; 268 for (i = 0; tlen > 0; i++, tlen -= len) { 269 len = min(PAGE_SIZE - ma_offs, tlen); 270 paddr = VM_PAGE_TO_PHYS(bp->bio_ma[i]) + ma_offs; 271 error = sglist_append_phys(sg, paddr, len); 272 if (error) { 273 SGLIST_RESTORE(sg, save); 274 return (error); 275 } 276 ma_offs = 0; 277 } 278 return (0); 279 } 280 281 /* 282 * Append a single physical address range to a scatter/gather list. 283 * If there are insufficient segments, then this fails with EFBIG. 284 */ 285 int 286 sglist_append_phys(struct sglist *sg, vm_paddr_t paddr, size_t len) 287 { 288 struct sglist_seg *ss; 289 struct sgsave save; 290 int error; 291 292 if (sg->sg_maxseg == 0) 293 return (EINVAL); 294 if (len == 0) 295 return (0); 296 297 if (sg->sg_nseg == 0) { 298 sg->sg_segs[0].ss_paddr = paddr; 299 sg->sg_segs[0].ss_len = len; 300 sg->sg_nseg = 1; 301 return (0); 302 } 303 ss = &sg->sg_segs[sg->sg_nseg - 1]; 304 SGLIST_SAVE(sg, save); 305 error = _sglist_append_range(sg, &ss, paddr, len); 306 if (error) 307 SGLIST_RESTORE(sg, save); 308 return (error); 309 } 310 311 /* 312 * Append the segments that describe a single mbuf chain to a 313 * scatter/gather list. If there are insufficient segments, then this 314 * fails with EFBIG. 315 */ 316 int 317 sglist_append_mbuf(struct sglist *sg, struct mbuf *m0) 318 { 319 struct sgsave save; 320 struct mbuf *m; 321 int error; 322 323 if (sg->sg_maxseg == 0) 324 return (EINVAL); 325 326 error = 0; 327 SGLIST_SAVE(sg, save); 328 for (m = m0; m != NULL; m = m->m_next) { 329 if (m->m_len > 0) { 330 error = sglist_append(sg, m->m_data, m->m_len); 331 if (error) { 332 SGLIST_RESTORE(sg, save); 333 return (error); 334 } 335 } 336 } 337 return (0); 338 } 339 340 /* 341 * Append the segments that describe a single user address range to a 342 * scatter/gather list. If there are insufficient segments, then this 343 * fails with EFBIG. 344 */ 345 int 346 sglist_append_user(struct sglist *sg, void *buf, size_t len, struct thread *td) 347 { 348 struct sgsave save; 349 int error; 350 351 if (sg->sg_maxseg == 0) 352 return (EINVAL); 353 SGLIST_SAVE(sg, save); 354 error = _sglist_append_buf(sg, buf, len, 355 vmspace_pmap(td->td_proc->p_vmspace), NULL); 356 if (error) 357 SGLIST_RESTORE(sg, save); 358 return (error); 359 } 360 361 /* 362 * Append the segments that describe a single uio to a scatter/gather 363 * list. If there are insufficient segments, then this fails with 364 * EFBIG. 365 */ 366 int 367 sglist_append_uio(struct sglist *sg, struct uio *uio) 368 { 369 struct iovec *iov; 370 struct sgsave save; 371 size_t resid, minlen; 372 pmap_t pmap; 373 int error, i; 374 375 if (sg->sg_maxseg == 0) 376 return (EINVAL); 377 378 resid = uio->uio_resid; 379 iov = uio->uio_iov; 380 381 if (uio->uio_segflg == UIO_USERSPACE) { 382 KASSERT(uio->uio_td != NULL, 383 ("sglist_append_uio: USERSPACE but no thread")); 384 pmap = vmspace_pmap(uio->uio_td->td_proc->p_vmspace); 385 } else 386 pmap = NULL; 387 388 error = 0; 389 SGLIST_SAVE(sg, save); 390 for (i = 0; i < uio->uio_iovcnt && resid != 0; i++) { 391 /* 392 * Now at the first iovec to load. Load each iovec 393 * until we have exhausted the residual count. 394 */ 395 minlen = MIN(resid, iov[i].iov_len); 396 if (minlen > 0) { 397 error = _sglist_append_buf(sg, iov[i].iov_base, minlen, 398 pmap, NULL); 399 if (error) { 400 SGLIST_RESTORE(sg, save); 401 return (error); 402 } 403 resid -= minlen; 404 } 405 } 406 return (0); 407 } 408 409 /* 410 * Append the segments that describe at most 'resid' bytes from a 411 * single uio to a scatter/gather list. If there are insufficient 412 * segments, then only the amount that fits is appended. 413 */ 414 int 415 sglist_consume_uio(struct sglist *sg, struct uio *uio, size_t resid) 416 { 417 struct iovec *iov; 418 size_t done; 419 pmap_t pmap; 420 int error, len; 421 422 if (sg->sg_maxseg == 0) 423 return (EINVAL); 424 425 if (uio->uio_segflg == UIO_USERSPACE) { 426 KASSERT(uio->uio_td != NULL, 427 ("sglist_consume_uio: USERSPACE but no thread")); 428 pmap = vmspace_pmap(uio->uio_td->td_proc->p_vmspace); 429 } else 430 pmap = NULL; 431 432 error = 0; 433 while (resid > 0 && uio->uio_resid) { 434 iov = uio->uio_iov; 435 len = iov->iov_len; 436 if (len == 0) { 437 uio->uio_iov++; 438 uio->uio_iovcnt--; 439 continue; 440 } 441 if (len > resid) 442 len = resid; 443 444 /* 445 * Try to append this iovec. If we run out of room, 446 * then break out of the loop. 447 */ 448 error = _sglist_append_buf(sg, iov->iov_base, len, pmap, &done); 449 iov->iov_base = (char *)iov->iov_base + done; 450 iov->iov_len -= done; 451 uio->uio_resid -= done; 452 uio->uio_offset += done; 453 resid -= done; 454 if (error) 455 break; 456 } 457 return (0); 458 } 459 460 /* 461 * Allocate and populate a scatter/gather list to describe a single 462 * kernel virtual address range. 463 */ 464 struct sglist * 465 sglist_build(void *buf, size_t len, int mflags) 466 { 467 struct sglist *sg; 468 int nsegs; 469 470 if (len == 0) 471 return (NULL); 472 473 nsegs = sglist_count(buf, len); 474 sg = sglist_alloc(nsegs, mflags); 475 if (sg == NULL) 476 return (NULL); 477 if (sglist_append(sg, buf, len) != 0) { 478 sglist_free(sg); 479 return (NULL); 480 } 481 return (sg); 482 } 483 484 /* 485 * Clone a new copy of a scatter/gather list. 486 */ 487 struct sglist * 488 sglist_clone(struct sglist *sg, int mflags) 489 { 490 struct sglist *new; 491 492 if (sg == NULL) 493 return (NULL); 494 new = sglist_alloc(sg->sg_maxseg, mflags); 495 if (new == NULL) 496 return (NULL); 497 new->sg_nseg = sg->sg_nseg; 498 bcopy(sg->sg_segs, new->sg_segs, sizeof(struct sglist_seg) * 499 sg->sg_nseg); 500 return (new); 501 } 502 503 /* 504 * Calculate the total length of the segments described in a 505 * scatter/gather list. 506 */ 507 size_t 508 sglist_length(struct sglist *sg) 509 { 510 size_t space; 511 int i; 512 513 space = 0; 514 for (i = 0; i < sg->sg_nseg; i++) 515 space += sg->sg_segs[i].ss_len; 516 return (space); 517 } 518 519 /* 520 * Split a scatter/gather list into two lists. The scatter/gather 521 * entries for the first 'length' bytes of the 'original' list are 522 * stored in the '*head' list and are removed from 'original'. 523 * 524 * If '*head' is NULL, then a new list will be allocated using 525 * 'mflags'. If M_NOWAIT is specified and the allocation fails, 526 * ENOMEM will be returned. 527 * 528 * If '*head' is not NULL, it should point to an empty sglist. If it 529 * does not have enough room for the remaining space, then EFBIG will 530 * be returned. If '*head' is not empty, then EINVAL will be 531 * returned. 532 * 533 * If 'original' is shared (refcount > 1), then EDOOFUS will be 534 * returned. 535 */ 536 int 537 sglist_split(struct sglist *original, struct sglist **head, size_t length, 538 int mflags) 539 { 540 struct sglist *sg; 541 size_t space, split; 542 int count, i; 543 544 if (original->sg_refs > 1) 545 return (EDOOFUS); 546 547 /* Figure out how big of a sglist '*head' has to hold. */ 548 count = 0; 549 space = 0; 550 split = 0; 551 for (i = 0; i < original->sg_nseg; i++) { 552 space += original->sg_segs[i].ss_len; 553 count++; 554 if (space >= length) { 555 /* 556 * If 'length' falls in the middle of a 557 * scatter/gather list entry, then 'split' 558 * holds how much of that entry will remain in 559 * 'original'. 560 */ 561 split = space - length; 562 break; 563 } 564 } 565 566 /* Nothing to do, so leave head empty. */ 567 if (count == 0) 568 return (0); 569 570 if (*head == NULL) { 571 sg = sglist_alloc(count, mflags); 572 if (sg == NULL) 573 return (ENOMEM); 574 *head = sg; 575 } else { 576 sg = *head; 577 if (sg->sg_maxseg < count) 578 return (EFBIG); 579 if (sg->sg_nseg != 0) 580 return (EINVAL); 581 } 582 583 /* Copy 'count' entries to 'sg' from 'original'. */ 584 bcopy(original->sg_segs, sg->sg_segs, count * 585 sizeof(struct sglist_seg)); 586 sg->sg_nseg = count; 587 588 /* 589 * If we had to split a list entry, fixup the last entry in 590 * 'sg' and the new first entry in 'original'. We also 591 * decrement 'count' by 1 since we will only be removing 592 * 'count - 1' segments from 'original' now. 593 */ 594 if (split != 0) { 595 count--; 596 sg->sg_segs[count].ss_len -= split; 597 original->sg_segs[count].ss_paddr = 598 sg->sg_segs[count].ss_paddr + split; 599 original->sg_segs[count].ss_len = split; 600 } 601 602 /* Trim 'count' entries from the front of 'original'. */ 603 original->sg_nseg -= count; 604 bcopy(original->sg_segs + count, original->sg_segs, count * 605 sizeof(struct sglist_seg)); 606 return (0); 607 } 608 609 /* 610 * Append the scatter/gather list elements in 'second' to the 611 * scatter/gather list 'first'. If there is not enough space in 612 * 'first', EFBIG is returned. 613 */ 614 int 615 sglist_join(struct sglist *first, struct sglist *second) 616 { 617 struct sglist_seg *flast, *sfirst; 618 int append; 619 620 /* If 'second' is empty, there is nothing to do. */ 621 if (second->sg_nseg == 0) 622 return (0); 623 624 /* 625 * If the first entry in 'second' can be appended to the last entry 626 * in 'first' then set append to '1'. 627 */ 628 append = 0; 629 flast = &first->sg_segs[first->sg_nseg - 1]; 630 sfirst = &second->sg_segs[0]; 631 if (first->sg_nseg != 0 && 632 flast->ss_paddr + flast->ss_len == sfirst->ss_paddr) 633 append = 1; 634 635 /* Make sure 'first' has enough room. */ 636 if (first->sg_nseg + second->sg_nseg - append > first->sg_maxseg) 637 return (EFBIG); 638 639 /* Merge last in 'first' and first in 'second' if needed. */ 640 if (append) 641 flast->ss_len += sfirst->ss_len; 642 643 /* Append new segments from 'second' to 'first'. */ 644 bcopy(first->sg_segs + first->sg_nseg, second->sg_segs + append, 645 (second->sg_nseg - append) * sizeof(struct sglist_seg)); 646 first->sg_nseg += second->sg_nseg - append; 647 sglist_reset(second); 648 return (0); 649 } 650 651 /* 652 * Generate a new scatter/gather list from a range of an existing 653 * scatter/gather list. The 'offset' and 'length' parameters specify 654 * the logical range of the 'original' list to extract. If that range 655 * is not a subset of the length of 'original', then EINVAL is 656 * returned. The new scatter/gather list is stored in '*slice'. 657 * 658 * If '*slice' is NULL, then a new list will be allocated using 659 * 'mflags'. If M_NOWAIT is specified and the allocation fails, 660 * ENOMEM will be returned. 661 * 662 * If '*slice' is not NULL, it should point to an empty sglist. If it 663 * does not have enough room for the remaining space, then EFBIG will 664 * be returned. If '*slice' is not empty, then EINVAL will be 665 * returned. 666 */ 667 int 668 sglist_slice(struct sglist *original, struct sglist **slice, size_t offset, 669 size_t length, int mflags) 670 { 671 struct sglist *sg; 672 size_t space, end, foffs, loffs; 673 int count, i, fseg; 674 675 /* Nothing to do. */ 676 if (length == 0) 677 return (0); 678 679 /* Figure out how many segments '*slice' needs to have. */ 680 end = offset + length; 681 space = 0; 682 count = 0; 683 fseg = 0; 684 foffs = loffs = 0; 685 for (i = 0; i < original->sg_nseg; i++) { 686 space += original->sg_segs[i].ss_len; 687 if (space > offset) { 688 /* 689 * When we hit the first segment, store its index 690 * in 'fseg' and the offset into the first segment 691 * of 'offset' in 'foffs'. 692 */ 693 if (count == 0) { 694 fseg = i; 695 foffs = offset - (space - 696 original->sg_segs[i].ss_len); 697 CTR1(KTR_DEV, "sglist_slice: foffs = %08lx", 698 foffs); 699 } 700 count++; 701 702 /* 703 * When we hit the last segment, break out of 704 * the loop. Store the amount of extra space 705 * at the end of this segment in 'loffs'. 706 */ 707 if (space >= end) { 708 loffs = space - end; 709 CTR1(KTR_DEV, "sglist_slice: loffs = %08lx", 710 loffs); 711 break; 712 } 713 } 714 } 715 716 /* If we never hit 'end', then 'length' ran off the end, so fail. */ 717 if (space < end) 718 return (EINVAL); 719 720 if (*slice == NULL) { 721 sg = sglist_alloc(count, mflags); 722 if (sg == NULL) 723 return (ENOMEM); 724 *slice = sg; 725 } else { 726 sg = *slice; 727 if (sg->sg_maxseg < count) 728 return (EFBIG); 729 if (sg->sg_nseg != 0) 730 return (EINVAL); 731 } 732 733 /* 734 * Copy over 'count' segments from 'original' starting at 735 * 'fseg' to 'sg'. 736 */ 737 bcopy(original->sg_segs + fseg, sg->sg_segs, 738 count * sizeof(struct sglist_seg)); 739 sg->sg_nseg = count; 740 741 /* Fixup first and last segments if needed. */ 742 if (foffs != 0) { 743 sg->sg_segs[0].ss_paddr += foffs; 744 sg->sg_segs[0].ss_len -= foffs; 745 CTR2(KTR_DEV, "sglist_slice seg[0]: %08lx:%08lx", 746 (long)sg->sg_segs[0].ss_paddr, sg->sg_segs[0].ss_len); 747 } 748 if (loffs != 0) { 749 sg->sg_segs[count - 1].ss_len -= loffs; 750 CTR2(KTR_DEV, "sglist_slice seg[%d]: len %08x", count - 1, 751 sg->sg_segs[count - 1].ss_len); 752 } 753 return (0); 754 } 755