Linux kernel & device driver programming

Cross-Referenced Linux and Device Driver Code

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Version: [ 2.6.11.8 ] [ 2.6.25 ] [ 2.6.25.8 ] [ 2.6.31.13 ] Architecture: [ i386 ]
  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);
295 
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