lib/scatterlist.c

   1 /*
   2  * Copyright (C) 2007 Jens Axboe <jens.axboe@oracle.com>
   3  *
   4  * Scatterlist handling helpers.
   5  *
   6  * This source code is licensed under the GNU General Public License,
   7  * Version 2. See the file COPYING for more details.
   8  */
   9 #include <linux/module.h>
  10 #include <linux/scatterlist.h>
  11
  12 /**
  13  * sg_next - return the next scatterlist entry in a list
  14  * @sg:         The current sg entry
  15  *
  16  * Description:
  17  *   Usually the next entry will be @sg@ + 1, but if this sg element is part
  18  *   of a chained scatterlist, it could jump to the start of a new
  19  *   scatterlist array.
  20  *
  21  **/
  22 struct scatterlist *sg_next(struct scatterlist *sg)
  23 {
  24 #ifdef CONFIG_DEBUG_SG
  25         BUG_ON(sg->sg_magic != SG_MAGIC);
  26 #endif
  27         if (sg_is_last(sg))
  28                 return NULL;
  29
  30         sg++;
  31         if (unlikely(sg_is_chain(sg)))
  32                 sg = sg_chain_ptr(sg);
  33
  34         return sg;
  35 }
  36 EXPORT_SYMBOL(sg_next);
  37
  38 /**
  39  * sg_last - return the last scatterlist entry in a list
  40  * @sgl:        First entry in the scatterlist
  41  * @nents:      Number of entries in the scatterlist
  42  *
  43  * Description:
  44  *   Should only be used casually, it (currently) scans the entire list
  45  *   to get the last entry.
  46  *
  47  *   Note that the @sgl@ pointer passed in need not be the first one,
  48  *   the important bit is that @nents@ denotes the number of entries that
  49  *   exist from @sgl@.
  50  *
  51  **/
  52 struct scatterlist *sg_last(struct scatterlist *sgl, unsigned int nents)
  53 {
  54 #ifndef ARCH_HAS_SG_CHAIN
  55         struct scatterlist *ret = &sgl[nents - 1];
  56 #else
  57         struct scatterlist *sg, *ret = NULL;
  58         unsigned int i;
  59
  60         for_each_sg(sgl, sg, nents, i)
  61                 ret = sg;
  62
  63 #endif
  64 #ifdef CONFIG_DEBUG_SG
  65         BUG_ON(sgl[0].sg_magic != SG_MAGIC);
  66         BUG_ON(!sg_is_last(ret));
  67 #endif
  68         return ret;
  69 }
  70 EXPORT_SYMBOL(sg_last);
  71
  72 /**
  73  * sg_init_table - Initialize SG table
  74  * @sgl:           The SG table
  75  * @nents:         Number of entries in table
  76  *
  77  * Notes:
  78  *   If this is part of a chained sg table, sg_mark_end() should be
  79  *   used only on the last table part.
  80  *
  81  **/
  82 void sg_init_table(struct scatterlist *sgl, unsigned int nents)
  83 {
  84         memset(sgl, 0, sizeof(*sgl) * nents);
  85 #ifdef CONFIG_DEBUG_SG
  86         {
  87                 unsigned int i;
  88                 for (i = 0; i < nents; i++)
  89                         sgl[i].sg_magic = SG_MAGIC;
  90         }
  91 #endif
  92         sg_mark_end(&sgl[nents - 1]);
  93 }
  94 EXPORT_SYMBOL(sg_init_table);
  95
  96 /**
  97  * sg_init_one - Initialize a single entry sg list
  98  * @sg:          SG entry
  99  * @buf:         Virtual address for IO
 100  * @buflen:      IO length
 101  *
 102  **/
 103 void sg_init_one(struct scatterlist *sg, const void *buf, unsigned int buflen)
 104 {
 105         sg_init_table(sg, 1);
 106         sg_set_buf(sg, buf, buflen);
 107 }
 108 EXPORT_SYMBOL(sg_init_one);
 109
 110 /*
 111  * The default behaviour of sg_alloc_table() is to use these kmalloc/kfree
 112  * helpers.
 113  */
 114 static struct scatterlist *sg_kmalloc(unsigned int nents, gfp_t gfp_mask)
 115 {
 116         if (nents == SG_MAX_SINGLE_ALLOC)
 117                 return (struct scatterlist *) __get_free_page(gfp_mask);
 118         else
 119                 return kmalloc(nents * sizeof(struct scatterlist), gfp_mask);
 120 }
 121
 122 static void sg_kfree(struct scatterlist *sg, unsigned int nents)
 123 {
 124         if (nents == SG_MAX_SINGLE_ALLOC)
 125                 free_page((unsigned long) sg);
 126         else
 127                 kfree(sg);
 128 }
 129
 130 /**
 131  * __sg_free_table - Free a previously mapped sg table
 132  * @table:      The sg table header to use
 133  * @max_ents:   The maximum number of entries per single scatterlist
 134  * @free_fn:    Free function
 135  *
 136  *  Description:
 137  *    Free an sg table previously allocated and setup with
 138  *    __sg_alloc_table().  The @max_ents value must be identical to
 139  *    that previously used with __sg_alloc_table().
 140  *
 141  **/
 142 void __sg_free_table(struct sg_table *table, unsigned int max_ents,
 143                      sg_free_fn *free_fn)
 144 {
 145         struct scatterlist *sgl, *next;
 146
 147         if (unlikely(!table->sgl))
 148                 return;
 149
 150         sgl = table->sgl;
 151         while (table->orig_nents) {
 152                 unsigned int alloc_size = table->orig_nents;
 153                 unsigned int sg_size;
 154
 155                 /*
 156                  * If we have more than max_ents segments left,
 157                  * then assign 'next' to the sg table after the current one.
 158                  * sg_size is then one less than alloc size, since the last
 159                  * element is the chain pointer.
 160                  */
 161                 if (alloc_size > max_ents) {
 162                         next = sg_chain_ptr(&sgl[max_ents - 1]);
 163                         alloc_size = max_ents;
 164                         sg_size = alloc_size - 1;
 165                 } else {
 166                         sg_size = alloc_size;
 167                         next = NULL;
 168                 }
 169
 170                 table->orig_nents -= sg_size;
 171                 free_fn(sgl, alloc_size);
 172                 sgl = next;
 173         }
 174
 175         table->sgl = NULL;
 176 }
 177 EXPORT_SYMBOL(__sg_free_table);
 178
 179 /**
 180  * sg_free_table - Free a previously allocated sg table
 181  * @table:      The mapped sg table header
 182  *
 183  **/
 184 void sg_free_table(struct sg_table *table)
 185 {
 186         __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
 187 }
 188 EXPORT_SYMBOL(sg_free_table);
 189
 190 /**
 191  * __sg_alloc_table - Allocate and initialize an sg table with given allocator
 192  * @table:      The sg table header to use
 193  * @nents:      Number of entries in sg list
 194  * @max_ents:   The maximum number of entries the allocator returns per call
 195  * @gfp_mask:   GFP allocation mask
 196  * @alloc_fn:   Allocator to use
 197  *
 198  * Description:
 199  *   This function returns a @table @nents long. The allocator is
 200  *   defined to return scatterlist chunks of maximum size @max_ents.
 201  *   Thus if @nents is bigger than @max_ents, the scatterlists will be
 202  *   chained in units of @max_ents.
 203  *
 204  * Notes:
 205  *   If this function returns non-0 (eg failure), the caller must call
 206  *   __sg_free_table() to cleanup any leftover allocations.
 207  *
 208  **/
 209 int __sg_alloc_table(struct sg_table *table, unsigned int nents,
 210                      unsigned int max_ents, gfp_t gfp_mask,
 211                      sg_alloc_fn *alloc_fn)
 212 {
 213         struct scatterlist *sg, *prv;
 214         unsigned int left;
 215
 216 #ifndef ARCH_HAS_SG_CHAIN
 217         BUG_ON(nents > max_ents);
 218 #endif
 219
 220         memset(table, 0, sizeof(*table));
 221
 222         left = nents;
 223         prv = NULL;
 224         do {
 225                 unsigned int sg_size, alloc_size = left;
 226
 227                 if (alloc_size > max_ents) {
 228                         alloc_size = max_ents;
 229                         sg_size = alloc_size - 1;
 230                 } else
 231                         sg_size = alloc_size;
 232
 233                 left -= sg_size;
 234
 235                 sg = alloc_fn(alloc_size, gfp_mask);
 236                 if (unlikely(!sg))
 237                         return -ENOMEM;
 238
 239                 sg_init_table(sg, alloc_size);
 240                 table->nents = table->orig_nents += sg_size;
 241
 242                 /*
 243                  * If this is the first mapping, assign the sg table header.
 244                  * If this is not the first mapping, chain previous part.
 245                  */
 246                 if (prv)
 247                         sg_chain(prv, max_ents, sg);
 248                 else
 249                         table->sgl = sg;
 250
 251                 /*
 252                  * If no more entries after this one, mark the end
 253                  */
 254                 if (!left)
 255                         sg_mark_end(&sg[sg_size - 1]);
 256
 257                 /*
 258                  * only really needed for mempool backed sg allocations (like
 259                  * SCSI), a possible improvement here would be to pass the
 260                  * table pointer into the allocator and let that clear these
 261                  * flags
 262                  */
 263                 gfp_mask &= ~__GFP_WAIT;
 264                 gfp_mask |= __GFP_HIGH;
 265                 prv = sg;
 266         } while (left);
 267
 268         return 0;
 269 }
 270 EXPORT_SYMBOL(__sg_alloc_table);
 271
 272 /**
 273  * sg_alloc_table - Allocate and initialize an sg table
 274  * @table:      The sg table header to use
 275  * @nents:      Number of entries in sg list
 276  * @gfp_mask:   GFP allocation mask
 277  *
 278  *  Description:
 279  *    Allocate and initialize an sg table. If @nents@ is larger than
 280  *    SG_MAX_SINGLE_ALLOC a chained sg table will be setup.
 281  *
 282  **/
 283 int sg_alloc_table(struct sg_table *table, unsigned int nents, gfp_t gfp_mask)
 284 {
 285         int ret;
 286
 287         ret = __sg_alloc_table(table, nents, SG_MAX_SINGLE_ALLOC,
 288                                gfp_mask, sg_kmalloc);
 289         if (unlikely(ret))
 290                 __sg_free_table(table, SG_MAX_SINGLE_ALLOC, sg_kfree);
 291
 292         return ret;
 293 }
 294 EXPORT_SYMBOL(sg_alloc_table);