lib/iov_iter.c

   1 #include <linux/export.h>
   2 #include <linux/uio.h>
   3 #include <linux/pagemap.h>
   4 #include <linux/slab.h>
   5 #include <linux/vmalloc.h>
   6 #include <net/checksum.h>
   7
   8 #define iterate_iovec(i, n, __v, __p, skip, STEP) {     \
   9         size_t left;                                    \
  10         size_t wanted = n;                              \
  11         __p = i->iov;                                   \
  12         __v.iov_len = min(n, __p->iov_len - skip);      \
  13         if (likely(__v.iov_len)) {                      \
  14                 __v.iov_base = __p->iov_base + skip;    \
  15                 left = (STEP);                          \
  16                 __v.iov_len -= left;                    \
  17                 skip += __v.iov_len;                    \
  18                 n -= __v.iov_len;                       \
  19         } else {                                        \
  20                 left = 0;                               \
  21         }                                               \
  22         while (unlikely(!left && n)) {                  \
  23                 __p++;                                  \
  24                 __v.iov_len = min(n, __p->iov_len);     \
  25                 if (unlikely(!__v.iov_len))             \
  26                         continue;                       \
  27                 __v.iov_base = __p->iov_base;           \
  28                 left = (STEP);                          \
  29                 __v.iov_len -= left;                    \
  30                 skip = __v.iov_len;                     \
  31                 n -= __v.iov_len;                       \
  32         }                                               \
  33         n = wanted - n;                                 \
  34 }
  35
  36 #define iterate_kvec(i, n, __v, __p, skip, STEP) {      \
  37         size_t wanted = n;                              \
  38         __p = i->kvec;                                  \
  39         __v.iov_len = min(n, __p->iov_len - skip);      \
  40         if (likely(__v.iov_len)) {                      \
  41                 __v.iov_base = __p->iov_base + skip;    \
  42                 (void)(STEP);                           \
  43                 skip += __v.iov_len;                    \
  44                 n -= __v.iov_len;                       \
  45         }                                               \
  46         while (unlikely(n)) {                           \
  47                 __p++;                                  \
  48                 __v.iov_len = min(n, __p->iov_len);     \
  49                 if (unlikely(!__v.iov_len))             \
  50                         continue;                       \
  51                 __v.iov_base = __p->iov_base;           \
  52                 (void)(STEP);                           \
  53                 skip = __v.iov_len;                     \
  54                 n -= __v.iov_len;                       \
  55         }                                               \
  56         n = wanted;                                     \
  57 }
  58
  59 #define iterate_bvec(i, n, __v, __p, skip, STEP) {      \
  60         size_t wanted = n;                              \
  61         __p = i->bvec;                                  \
  62         __v.bv_len = min_t(size_t, n, __p->bv_len - skip);      \
  63         if (likely(__v.bv_len)) {                       \
  64                 __v.bv_page = __p->bv_page;             \
  65                 __v.bv_offset = __p->bv_offset + skip;  \
  66                 (void)(STEP);                           \
  67                 skip += __v.bv_len;                     \
  68                 n -= __v.bv_len;                        \
  69         }                                               \
  70         while (unlikely(n)) {                           \
  71                 __p++;                                  \
  72                 __v.bv_len = min_t(size_t, n, __p->bv_len);     \
  73                 if (unlikely(!__v.bv_len))              \
  74                         continue;                       \
  75                 __v.bv_page = __p->bv_page;             \
  76                 __v.bv_offset = __p->bv_offset;         \
  77                 (void)(STEP);                           \
  78                 skip = __v.bv_len;                      \
  79                 n -= __v.bv_len;                        \
  80         }                                               \
  81         n = wanted;                                     \
  82 }
  83
  84 #define iterate_all_kinds(i, n, v, I, B, K) {                   \
  85         size_t skip = i->iov_offset;                            \
  86         if (unlikely(i->type & ITER_BVEC)) {                    \
  87                 const struct bio_vec *bvec;                     \
  88                 struct bio_vec v;                               \
  89                 iterate_bvec(i, n, v, bvec, skip, (B))          \
  90         } else if (unlikely(i->type & ITER_KVEC)) {             \
  91                 const struct kvec *kvec;                        \
  92                 struct kvec v;                                  \
  93                 iterate_kvec(i, n, v, kvec, skip, (K))          \
  94         } else {                                                \
  95                 const struct iovec *iov;                        \
  96                 struct iovec v;                                 \
  97                 iterate_iovec(i, n, v, iov, skip, (I))          \
  98         }                                                       \
  99 }
 100
 101 #define iterate_and_advance(i, n, v, I, B, K) {                 \
 102         size_t skip = i->iov_offset;                            \
 103         if (unlikely(i->type & ITER_BVEC)) {                    \
 104                 const struct bio_vec *bvec;                     \
 105                 struct bio_vec v;                               \
 106                 iterate_bvec(i, n, v, bvec, skip, (B))          \
 107                 if (skip == bvec->bv_len) {                     \
 108                         bvec++;                                 \
 109                         skip = 0;                               \
 110                 }                                               \
 111                 i->nr_segs -= bvec - i->bvec;                   \
 112                 i->bvec = bvec;                                 \
 113         } else if (unlikely(i->type & ITER_KVEC)) {             \
 114                 const struct kvec *kvec;                        \
 115                 struct kvec v;                                  \
 116                 iterate_kvec(i, n, v, kvec, skip, (K))          \
 117                 if (skip == kvec->iov_len) {                    \
 118                         kvec++;                                 \
 119                         skip = 0;                               \
 120                 }                                               \
 121                 i->nr_segs -= kvec - i->kvec;                   \
 122                 i->kvec = kvec;                                 \
 123         } else {                                                \
 124                 const struct iovec *iov;                        \
 125                 struct iovec v;                                 \
 126                 iterate_iovec(i, n, v, iov, skip, (I))          \
 127                 if (skip == iov->iov_len) {                     \
 128                         iov++;                                  \
 129                         skip = 0;                               \
 130                 }                                               \
 131                 i->nr_segs -= iov - i->iov;                     \
 132                 i->iov = iov;                                   \
 133         }                                                       \
 134         i->count -= n;                                          \
 135         i->iov_offset = skip;                                   \
 136 }
 137
 138 static size_t copy_page_to_iter_iovec(struct page *page, size_t offset, size_t bytes,
 139                          struct iov_iter *i)
 140 {
 141         size_t skip, copy, left, wanted;
 142         const struct iovec *iov;
 143         char __user *buf;
 144         void *kaddr, *from;
 145
 146         if (unlikely(bytes > i->count))
 147                 bytes = i->count;
 148
 149         if (unlikely(!bytes))
 150                 return 0;
 151
 152         wanted = bytes;
 153         iov = i->iov;
 154         skip = i->iov_offset;
 155         buf = iov->iov_base + skip;
 156         copy = min(bytes, iov->iov_len - skip);
 157
 158         if (!fault_in_pages_writeable(buf, copy)) {
 159                 kaddr = kmap_atomic(page);
 160                 from = kaddr + offset;
 161
 162                 /* first chunk, usually the only one */
 163                 left = __copy_to_user_inatomic(buf, from, copy);
 164                 copy -= left;
 165                 skip += copy;
 166                 from += copy;
 167                 bytes -= copy;
 168
 169                 while (unlikely(!left && bytes)) {
 170                         iov++;
 171                         buf = iov->iov_base;
 172                         copy = min(bytes, iov->iov_len);
 173                         left = __copy_to_user_inatomic(buf, from, copy);
 174                         copy -= left;
 175                         skip = copy;
 176                         from += copy;
 177                         bytes -= copy;
 178                 }
 179                 if (likely(!bytes)) {
 180                         kunmap_atomic(kaddr);
 181                         goto done;
 182                 }
 183                 offset = from - kaddr;
 184                 buf += copy;
 185                 kunmap_atomic(kaddr);
 186                 copy = min(bytes, iov->iov_len - skip);
 187         }
 188         /* Too bad - revert to non-atomic kmap */
 189         kaddr = kmap(page);
 190         from = kaddr + offset;
 191         left = __copy_to_user(buf, from, copy);
 192         copy -= left;
 193         skip += copy;
 194         from += copy;
 195         bytes -= copy;
 196         while (unlikely(!left && bytes)) {
 197                 iov++;
 198                 buf = iov->iov_base;
 199                 copy = min(bytes, iov->iov_len);
 200                 left = __copy_to_user(buf, from, copy);
 201                 copy -= left;
 202                 skip = copy;
 203                 from += copy;
 204                 bytes -= copy;
 205         }
 206         kunmap(page);
 207 done:
 208         if (skip == iov->iov_len) {
 209                 iov++;
 210                 skip = 0;
 211         }
 212         i->count -= wanted - bytes;
 213         i->nr_segs -= iov - i->iov;
 214         i->iov = iov;
 215         i->iov_offset = skip;
 216         return wanted - bytes;
 217 }
 218
 219 static size_t copy_page_from_iter_iovec(struct page *page, size_t offset, size_t bytes,
 220                          struct iov_iter *i)
 221 {
 222         size_t skip, copy, left, wanted;
 223         const struct iovec *iov;
 224         char __user *buf;
 225         void *kaddr, *to;
 226
 227         if (unlikely(bytes > i->count))
 228                 bytes = i->count;
 229
 230         if (unlikely(!bytes))
 231                 return 0;
 232
 233         wanted = bytes;
 234         iov = i->iov;
 235         skip = i->iov_offset;
 236         buf = iov->iov_base + skip;
 237         copy = min(bytes, iov->iov_len - skip);
 238
 239         if (!fault_in_pages_readable(buf, copy)) {
 240                 kaddr = kmap_atomic(page);
 241                 to = kaddr + offset;
 242
 243                 /* first chunk, usually the only one */
 244                 left = __copy_from_user_inatomic(to, buf, copy);
 245                 copy -= left;
 246                 skip += copy;
 247                 to += copy;
 248                 bytes -= copy;
 249
 250                 while (unlikely(!left && bytes)) {
 251                         iov++;
 252                         buf = iov->iov_base;
 253                         copy = min(bytes, iov->iov_len);
 254                         left = __copy_from_user_inatomic(to, buf, copy);
 255                         copy -= left;
 256                         skip = copy;
 257                         to += copy;
 258                         bytes -= copy;
 259                 }
 260                 if (likely(!bytes)) {
 261                         kunmap_atomic(kaddr);
 262                         goto done;
 263                 }
 264                 offset = to - kaddr;
 265                 buf += copy;
 266                 kunmap_atomic(kaddr);
 267                 copy = min(bytes, iov->iov_len - skip);
 268         }
 269         /* Too bad - revert to non-atomic kmap */
 270         kaddr = kmap(page);
 271         to = kaddr + offset;
 272         left = __copy_from_user(to, buf, copy);
 273         copy -= left;
 274         skip += copy;
 275         to += copy;
 276         bytes -= copy;
 277         while (unlikely(!left && bytes)) {
 278                 iov++;
 279                 buf = iov->iov_base;
 280                 copy = min(bytes, iov->iov_len);
 281                 left = __copy_from_user(to, buf, copy);
 282                 copy -= left;
 283                 skip = copy;
 284                 to += copy;
 285                 bytes -= copy;
 286         }
 287         kunmap(page);
 288 done:
 289         if (skip == iov->iov_len) {
 290                 iov++;
 291                 skip = 0;
 292         }
 293         i->count -= wanted - bytes;
 294         i->nr_segs -= iov - i->iov;
 295         i->iov = iov;
 296         i->iov_offset = skip;
 297         return wanted - bytes;
 298 }
 299
 300 /*
 301  * Fault in the first iovec of the given iov_iter, to a maximum length
 302  * of bytes. Returns 0 on success, or non-zero if the memory could not be
 303  * accessed (ie. because it is an invalid address).
 304  *
 305  * writev-intensive code may want this to prefault several iovecs -- that
 306  * would be possible (callers must not rely on the fact that _only_ the
 307  * first iovec will be faulted with the current implementation).
 308  */
 309 int iov_iter_fault_in_readable(struct iov_iter *i, size_t bytes)
 310 {
 311         if (!(i->type & (ITER_BVEC|ITER_KVEC))) {
 312                 char __user *buf = i->iov->iov_base + i->iov_offset;
 313                 bytes = min(bytes, i->iov->iov_len - i->iov_offset);
 314                 return fault_in_pages_readable(buf, bytes);
 315         }
 316         return 0;
 317 }
 318 EXPORT_SYMBOL(iov_iter_fault_in_readable);
 319
 320 void iov_iter_init(struct iov_iter *i, int direction,
 321                         const struct iovec *iov, unsigned long nr_segs,
 322                         size_t count)
 323 {
 324         /* It will get better.  Eventually... */
 325         if (segment_eq(get_fs(), KERNEL_DS)) {
 326                 direction |= ITER_KVEC;
 327                 i->type = direction;
 328                 i->kvec = (struct kvec *)iov;
 329         } else {
 330                 i->type = direction;
 331                 i->iov = iov;
 332         }
 333         i->nr_segs = nr_segs;
 334         i->iov_offset = 0;
 335         i->count = count;
 336 }
 337 EXPORT_SYMBOL(iov_iter_init);
 338
 339 static void memcpy_from_page(char *to, struct page *page, size_t offset, size_t len)
 340 {
 341         char *from = kmap_atomic(page);
 342         memcpy(to, from + offset, len);
 343         kunmap_atomic(from);
 344 }
 345
 346 static void memcpy_to_page(struct page *page, size_t offset, char *from, size_t len)
 347 {
 348         char *to = kmap_atomic(page);
 349         memcpy(to + offset, from, len);
 350         kunmap_atomic(to);
 351 }
 352
 353 static void memzero_page(struct page *page, size_t offset, size_t len)
 354 {
 355         char *addr = kmap_atomic(page);
 356         memset(addr + offset, 0, len);
 357         kunmap_atomic(addr);
 358 }
 359
 360 size_t copy_to_iter(void *addr, size_t bytes, struct iov_iter *i)
 361 {
 362         char *from = addr;
 363         if (unlikely(bytes > i->count))
 364                 bytes = i->count;
 365
 366         if (unlikely(!bytes))
 367                 return 0;
 368
 369         iterate_and_advance(i, bytes, v,
 370                 __copy_to_user(v.iov_base, (from += v.iov_len) - v.iov_len,
 371                                v.iov_len),
 372                 memcpy_to_page(v.bv_page, v.bv_offset,
 373                                (from += v.bv_len) - v.bv_len, v.bv_len),
 374                 memcpy(v.iov_base, (from += v.iov_len) - v.iov_len, v.iov_len)
 375         )
 376
 377         return bytes;
 378 }
 379 EXPORT_SYMBOL(copy_to_iter);
 380
 381 size_t copy_from_iter(void *addr, size_t bytes, struct iov_iter *i)
 382 {
 383         char *to = addr;
 384         if (unlikely(bytes > i->count))
 385                 bytes = i->count;
 386
 387         if (unlikely(!bytes))
 388                 return 0;
 389
 390         iterate_and_advance(i, bytes, v,
 391                 __copy_from_user((to += v.iov_len) - v.iov_len, v.iov_base,
 392                                  v.iov_len),
 393                 memcpy_from_page((to += v.bv_len) - v.bv_len, v.bv_page,
 394                                  v.bv_offset, v.bv_len),
 395                 memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
 396         )
 397
 398         return bytes;
 399 }
 400 EXPORT_SYMBOL(copy_from_iter);
 401
 402 size_t copy_from_iter_nocache(void *addr, size_t bytes, struct iov_iter *i)
 403 {
 404         char *to = addr;
 405         if (unlikely(bytes > i->count))
 406                 bytes = i->count;
 407
 408         if (unlikely(!bytes))
 409                 return 0;
 410
 411         iterate_and_advance(i, bytes, v,
 412                 __copy_from_user_nocache((to += v.iov_len) - v.iov_len,
 413                                          v.iov_base, v.iov_len),
 414                 memcpy_from_page((to += v.bv_len) - v.bv_len, v.bv_page,
 415                                  v.bv_offset, v.bv_len),
 416                 memcpy((to += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
 417         )
 418
 419         return bytes;
 420 }
 421 EXPORT_SYMBOL(copy_from_iter_nocache);
 422
 423 size_t copy_page_to_iter(struct page *page, size_t offset, size_t bytes,
 424                          struct iov_iter *i)
 425 {
 426         if (i->type & (ITER_BVEC|ITER_KVEC)) {
 427                 void *kaddr = kmap_atomic(page);
 428                 size_t wanted = copy_to_iter(kaddr + offset, bytes, i);
 429                 kunmap_atomic(kaddr);
 430                 return wanted;
 431         } else
 432                 return copy_page_to_iter_iovec(page, offset, bytes, i);
 433 }
 434 EXPORT_SYMBOL(copy_page_to_iter);
 435
 436 size_t copy_page_from_iter(struct page *page, size_t offset, size_t bytes,
 437                          struct iov_iter *i)
 438 {
 439         if (i->type & (ITER_BVEC|ITER_KVEC)) {
 440                 void *kaddr = kmap_atomic(page);
 441                 size_t wanted = copy_from_iter(kaddr + offset, bytes, i);
 442                 kunmap_atomic(kaddr);
 443                 return wanted;
 444         } else
 445                 return copy_page_from_iter_iovec(page, offset, bytes, i);
 446 }
 447 EXPORT_SYMBOL(copy_page_from_iter);
 448
 449 size_t iov_iter_zero(size_t bytes, struct iov_iter *i)
 450 {
 451         if (unlikely(bytes > i->count))
 452                 bytes = i->count;
 453
 454         if (unlikely(!bytes))
 455                 return 0;
 456
 457         iterate_and_advance(i, bytes, v,
 458                 __clear_user(v.iov_base, v.iov_len),
 459                 memzero_page(v.bv_page, v.bv_offset, v.bv_len),
 460                 memset(v.iov_base, 0, v.iov_len)
 461         )
 462
 463         return bytes;
 464 }
 465 EXPORT_SYMBOL(iov_iter_zero);
 466
 467 size_t iov_iter_copy_from_user_atomic(struct page *page,
 468                 struct iov_iter *i, unsigned long offset, size_t bytes)
 469 {
 470         char *kaddr = kmap_atomic(page), *p = kaddr + offset;
 471         iterate_all_kinds(i, bytes, v,
 472                 __copy_from_user_inatomic((p += v.iov_len) - v.iov_len,
 473                                           v.iov_base, v.iov_len),
 474                 memcpy_from_page((p += v.bv_len) - v.bv_len, v.bv_page,
 475                                  v.bv_offset, v.bv_len),
 476                 memcpy((p += v.iov_len) - v.iov_len, v.iov_base, v.iov_len)
 477         )
 478         kunmap_atomic(kaddr);
 479         return bytes;
 480 }
 481 EXPORT_SYMBOL(iov_iter_copy_from_user_atomic);
 482
 483 void iov_iter_advance(struct iov_iter *i, size_t size)
 484 {
 485         iterate_and_advance(i, size, v, 0, 0, 0)
 486 }
 487 EXPORT_SYMBOL(iov_iter_advance);
 488
 489 /*
 490  * Return the count of just the current iov_iter segment.
 491  */
 492 size_t iov_iter_single_seg_count(const struct iov_iter *i)
 493 {
 494         if (i->nr_segs == 1)
 495                 return i->count;
 496         else if (i->type & ITER_BVEC)
 497                 return min(i->count, i->bvec->bv_len - i->iov_offset);
 498         else
 499                 return min(i->count, i->iov->iov_len - i->iov_offset);
 500 }
 501 EXPORT_SYMBOL(iov_iter_single_seg_count);
 502
 503 void iov_iter_kvec(struct iov_iter *i, int direction,
 504                         const struct kvec *kvec, unsigned long nr_segs,
 505                         size_t count)
 506 {
 507         BUG_ON(!(direction & ITER_KVEC));
 508         i->type = direction;
 509         i->kvec = kvec;
 510         i->nr_segs = nr_segs;
 511         i->iov_offset = 0;
 512         i->count = count;
 513 }
 514 EXPORT_SYMBOL(iov_iter_kvec);
 515
 516 void iov_iter_bvec(struct iov_iter *i, int direction,
 517                         const struct bio_vec *bvec, unsigned long nr_segs,
 518                         size_t count)
 519 {
 520         BUG_ON(!(direction & ITER_BVEC));
 521         i->type = direction;
 522         i->bvec = bvec;
 523         i->nr_segs = nr_segs;
 524         i->iov_offset = 0;
 525         i->count = count;
 526 }
 527 EXPORT_SYMBOL(iov_iter_bvec);
 528
 529 unsigned long iov_iter_alignment(const struct iov_iter *i)
 530 {
 531         unsigned long res = 0;
 532         size_t size = i->count;
 533
 534         if (!size)
 535                 return 0;
 536
 537         iterate_all_kinds(i, size, v,
 538                 (res |= (unsigned long)v.iov_base | v.iov_len, 0),
 539                 res |= v.bv_offset | v.bv_len,
 540                 res |= (unsigned long)v.iov_base | v.iov_len
 541         )
 542         return res;
 543 }
 544 EXPORT_SYMBOL(iov_iter_alignment);
 545
 546 ssize_t iov_iter_get_pages(struct iov_iter *i,
 547                    struct page **pages, size_t maxsize, unsigned maxpages,
 548                    size_t *start)
 549 {
 550         if (maxsize > i->count)
 551                 maxsize = i->count;
 552
 553         if (!maxsize)
 554                 return 0;
 555
 556         iterate_all_kinds(i, maxsize, v, ({
 557                 unsigned long addr = (unsigned long)v.iov_base;
 558                 size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
 559                 int n;
 560                 int res;
 561
 562                 if (len > maxpages * PAGE_SIZE)
 563                         len = maxpages * PAGE_SIZE;
 564                 addr &= ~(PAGE_SIZE - 1);
 565                 n = DIV_ROUND_UP(len, PAGE_SIZE);
 566                 res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, pages);
 567                 if (unlikely(res < 0))
 568                         return res;
 569                 return (res == n ? len : res * PAGE_SIZE) - *start;
 570         0;}),({
 571                 /* can't be more than PAGE_SIZE */
 572                 *start = v.bv_offset;
 573                 get_page(*pages = v.bv_page);
 574                 return v.bv_len;
 575         }),({
 576                 return -EFAULT;
 577         })
 578         )
 579         return 0;
 580 }
 581 EXPORT_SYMBOL(iov_iter_get_pages);
 582
 583 static struct page **get_pages_array(size_t n)
 584 {
 585         struct page **p = kmalloc(n * sizeof(struct page *), GFP_KERNEL);
 586         if (!p)
 587                 p = vmalloc(n * sizeof(struct page *));
 588         return p;
 589 }
 590
 591 ssize_t iov_iter_get_pages_alloc(struct iov_iter *i,
 592                    struct page ***pages, size_t maxsize,
 593                    size_t *start)
 594 {
 595         struct page **p;
 596
 597         if (maxsize > i->count)
 598                 maxsize = i->count;
 599
 600         if (!maxsize)
 601                 return 0;
 602
 603         iterate_all_kinds(i, maxsize, v, ({
 604                 unsigned long addr = (unsigned long)v.iov_base;
 605                 size_t len = v.iov_len + (*start = addr & (PAGE_SIZE - 1));
 606                 int n;
 607                 int res;
 608
 609                 addr &= ~(PAGE_SIZE - 1);
 610                 n = DIV_ROUND_UP(len, PAGE_SIZE);
 611                 p = get_pages_array(n);
 612                 if (!p)
 613                         return -ENOMEM;
 614                 res = get_user_pages_fast(addr, n, (i->type & WRITE) != WRITE, p);
 615                 if (unlikely(res < 0)) {
 616                         kvfree(p);
 617                         return res;
 618                 }
 619                 *pages = p;
 620                 return (res == n ? len : res * PAGE_SIZE) - *start;
 621         0;}),({
 622                 /* can't be more than PAGE_SIZE */
 623                 *start = v.bv_offset;
 624                 *pages = p = get_pages_array(1);
 625                 if (!p)
 626                         return -ENOMEM;
 627                 get_page(*p = v.bv_page);
 628                 return v.bv_len;
 629         }),({
 630                 return -EFAULT;
 631         })
 632         )
 633         return 0;
 634 }
 635 EXPORT_SYMBOL(iov_iter_get_pages_alloc);
 636
 637 size_t csum_and_copy_from_iter(void *addr, size_t bytes, __wsum *csum,
 638                                struct iov_iter *i)
 639 {
 640         char *to = addr;
 641         __wsum sum, next;
 642         size_t off = 0;
 643         if (unlikely(bytes > i->count))
 644                 bytes = i->count;
 645
 646         if (unlikely(!bytes))
 647                 return 0;
 648
 649         sum = *csum;
 650         iterate_and_advance(i, bytes, v, ({
 651                 int err = 0;
 652                 next = csum_and_copy_from_user(v.iov_base,
 653                                                (to += v.iov_len) - v.iov_len,
 654                                                v.iov_len, 0, &err);
 655                 if (!err) {
 656                         sum = csum_block_add(sum, next, off);
 657                         off += v.iov_len;
 658                 }
 659                 err ? v.iov_len : 0;
 660         }), ({
 661                 char *p = kmap_atomic(v.bv_page);
 662                 next = csum_partial_copy_nocheck(p + v.bv_offset,
 663                                                  (to += v.bv_len) - v.bv_len,
 664                                                  v.bv_len, 0);
 665                 kunmap_atomic(p);
 666                 sum = csum_block_add(sum, next, off);
 667                 off += v.bv_len;
 668         }),({
 669                 next = csum_partial_copy_nocheck(v.iov_base,
 670                                                  (to += v.iov_len) - v.iov_len,
 671                                                  v.iov_len, 0);
 672                 sum = csum_block_add(sum, next, off);
 673                 off += v.iov_len;
 674         })
 675         )
 676         *csum = sum;
 677         return bytes;
 678 }
 679 EXPORT_SYMBOL(csum_and_copy_from_iter);
 680
 681 size_t csum_and_copy_to_iter(void *addr, size_t bytes, __wsum *csum,
 682                              struct iov_iter *i)
 683 {
 684         char *from = addr;
 685         __wsum sum, next;
 686         size_t off = 0;
 687         if (unlikely(bytes > i->count))
 688                 bytes = i->count;
 689
 690         if (unlikely(!bytes))
 691                 return 0;
 692
 693         sum = *csum;
 694         iterate_and_advance(i, bytes, v, ({
 695                 int err = 0;
 696                 next = csum_and_copy_to_user((from += v.iov_len) - v.iov_len,
 697                                              v.iov_base,
 698                                              v.iov_len, 0, &err);
 699                 if (!err) {
 700                         sum = csum_block_add(sum, next, off);
 701                         off += v.iov_len;
 702                 }
 703                 err ? v.iov_len : 0;
 704         }), ({
 705                 char *p = kmap_atomic(v.bv_page);
 706                 next = csum_partial_copy_nocheck((from += v.bv_len) - v.bv_len,
 707                                                  p + v.bv_offset,
 708                                                  v.bv_len, 0);
 709                 kunmap_atomic(p);
 710                 sum = csum_block_add(sum, next, off);
 711                 off += v.bv_len;
 712         }),({
 713                 next = csum_partial_copy_nocheck((from += v.iov_len) - v.iov_len,
 714                                                  v.iov_base,
 715                                                  v.iov_len, 0);
 716                 sum = csum_block_add(sum, next, off);
 717                 off += v.iov_len;
 718         })
 719         )
 720         *csum = sum;
 721         return bytes;
 722 }
 723 EXPORT_SYMBOL(csum_and_copy_to_iter);
 724
 725 int iov_iter_npages(const struct iov_iter *i, int maxpages)
 726 {
 727         size_t size = i->count;
 728         int npages = 0;
 729
 730         if (!size)
 731                 return 0;
 732
 733         iterate_all_kinds(i, size, v, ({
 734                 unsigned long p = (unsigned long)v.iov_base;
 735                 npages += DIV_ROUND_UP(p + v.iov_len, PAGE_SIZE)
 736                         - p / PAGE_SIZE;
 737                 if (npages >= maxpages)
 738                         return maxpages;
 739         0;}),({
 740                 npages++;
 741                 if (npages >= maxpages)
 742                         return maxpages;
 743         }),({
 744                 unsigned long p = (unsigned long)v.iov_base;
 745                 npages += DIV_ROUND_UP(p + v.iov_len, PAGE_SIZE)
 746                         - p / PAGE_SIZE;
 747                 if (npages >= maxpages)
 748                         return maxpages;
 749         })
 750         )
 751         return npages;
 752 }
 753 EXPORT_SYMBOL(iov_iter_npages);
 754
 755 const void *dup_iter(struct iov_iter *new, struct iov_iter *old, gfp_t flags)
 756 {
 757         *new = *old;
 758         if (new->type & ITER_BVEC)
 759                 return new->bvec = kmemdup(new->bvec,
 760                                     new->nr_segs * sizeof(struct bio_vec),
 761                                     flags);
 762         else
 763                 /* iovec and kvec have identical layout */
 764                 return new->iov = kmemdup(new->iov,
 765                                    new->nr_segs * sizeof(struct iovec),
 766                                    flags);
 767 }
 768 EXPORT_SYMBOL(dup_iter);