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| <section id="shared-memory"> |
| <h1>Shared Memory<a class="headerlink" href="#shared-memory" title="Permalink to this heading"></a></h1> |
| <p>Shared memory interfaces are only available with the NuttX kernel |
| build (<code class="docutils literal notranslate"><span class="pre">CONFIG_BUILD_KERNEL=y</span></code>). These interfaces support user |
| memory regions that can be shared between multiple user processes. |
| The user interfaces are provided in the standard header file |
| <code class="docutils literal notranslate"><span class="pre">include/sys/shm.h></span></code>. All logic to support shared memory is |
| implemented within the NuttX kernel with the exception of two |
| low-level functions that are require to configure the |
| platform-specific MMU resources. Those interfaces are described |
| below:</p> |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.up_shmat"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_shmat</span></span></span><span class="sig-paren">(</span><span class="pre">FAR</span><span class="w"> </span><span class="n"><span class="pre">uintptr_t</span></span><span class="w"> </span><span class="p"><span class="pre">*</span></span><span class="n"><span class="pre">pages</span></span>, <span class="kt"><span class="pre">unsigned</span></span><span class="w"> </span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">npages</span></span>, <span class="n"><span class="pre">uintptr_t</span></span><span class="w"> </span><span class="n"><span class="pre">vaddr</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_shmat" title="Permalink to this definition"></a><br /></dt> |
| <dd><p>Attach, i.e, map, on shared memory region to a user virtual address.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>pages</strong> – A pointer to the first element in a array of |
| physical address, each corresponding to one page of memory.</p></li> |
| <li><p><strong>npages</strong> – The number of pages in the list of physical pages |
| to be mapped.</p></li> |
| <li><p><strong>vaddr</strong> – The virtual address corresponding to the beginning |
| of the (contiguous) virtual address region.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p>Zero (OK) is returned on success; a negated errno value is returned on failure.</p> |
| </dd> |
| </dl> |
| </dd></dl> |
| |
| <dl class="c function"> |
| <dt class="sig sig-object c" id="c.up_shmdt"> |
| <span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="sig-name descname"><span class="n"><span class="pre">up_shmdt</span></span></span><span class="sig-paren">(</span><span class="n"><span class="pre">uintptr_t</span></span><span class="w"> </span><span class="n"><span class="pre">vaddr</span></span>, <span class="kt"><span class="pre">unsigned</span></span><span class="w"> </span><span class="kt"><span class="pre">int</span></span><span class="w"> </span><span class="n"><span class="pre">npages</span></span><span class="sig-paren">)</span><a class="headerlink" href="#c.up_shmdt" title="Permalink to this definition"></a><br /></dt> |
| <dd><p>Detach, i.e, unmap, on shared memory region from a user virtual address.</p> |
| <dl class="field-list simple"> |
| <dt class="field-odd">Parameters<span class="colon">:</span></dt> |
| <dd class="field-odd"><ul class="simple"> |
| <li><p><strong>vaddr</strong> – The virtual address corresponding to the beginning |
| of the (contiguous) virtual address region.</p></li> |
| <li><p><strong>npages</strong> – T The number of pages to be unmapped.</p></li> |
| </ul> |
| </dd> |
| <dt class="field-even">Returns<span class="colon">:</span></dt> |
| <dd class="field-even"><p>Zero (OK) is returned on success; a negated errno value is returned on failure.</p> |
| </dd> |
| </dl> |
| </dd></dl> |
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