linux_driver_model.html

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<a href=start.html>start</a></br>

<h4><a name="the_linux_driver_model" id="the_linux_driver_model">The Linux Driver Model</a></h4>
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<p>
This can best be described by examining a typical <strong>write</strong> system call. This is performed after an <strong>open</strong> call during which the kernel checks for  user permissions on the <strong>device node</strong> and then creates an entry in the file descriptor table for future device access.
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<p>
Following the <strong>open</strong> call the user process can then proceed to exchange data with the device using a number of methods. 
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<li class="level1"><div class="li"> read / write   send and receive buffers to and from the device</div>
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<li class="level1"><div class="li"> ioctl          send commands and a data buffer to the device </div>
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<li class="level1"><div class="li"> proc           examine driver characteristics and even perform full communications</div>
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<li class="level1"><div class="li"> poll / select  get notification when the device can provide or process data or has an exception</div>
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<li class="level1"><div class="li"> misc            a number of misc system calls to seek and get signals on io completion.</div>
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<p>
The user process uses an index into the file descriptor table to define the major number which in turn refers to a particular device driver which uses a file operations table to satisfy a system service call for a given device operation.
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<p>
In this example a user write call is shown.
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<p>
 <a href="media/ddfig.gif" class="media" target="_blank" title="ddfig.gif"><img src="media/ddfig.gif" class="media" alt="" /></a>
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<p>
 A block of data in user space is to be transfered to the device driver in kernel space for eventual distribution to the device.
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