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<title>fs/read_write.c</title>
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<a name='TOP'><h2><a href='../mains.html'>root</a>/<a href='../files/98.html'>fs</a>/read_write.c</h2>
<i><font color='green'>/* [<][>]<a href='#L37'>[^]</a><a href='#L126'>[v]</a>[top]<a href='#BOTTOM'>[bottom]</a><a href='../mains.html'>[index]</a><a href='../help.html'>[help]</a> */</font></i>
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<h2>DEFINITIONS</h2>
This source file includes following definitions.
<ol>
<li><a href='#L37' title='Defined at 37.'>sys_lseek</a>
<li><a href='#L84' title='Defined at 84.'>sys_read</a>
<li><a href='#L126' title='Defined at 126.'>sys_write</a>
</ol>
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<pre>
<a name='L1'><i><font color='green'>/*</font></i>
<a name='L2'><i><font color='green'>* linux/fs/read_write.c</font></i>
<a name='L3'><i><font color='green'>*</font></i>
<a name='L4'><i><font color='green'>* (C) 1991 Linus Torvalds</font></i>
<a name='L5'><i><font color='green'>*/</font></i>
<a name='L6'>
<a name='L7'><font color='darkred'>#include</font> <<a href='43.html'>sys/stat.h</a>> <i><font color='green'>// 文件状态头文件。含有文件或文件系统状态结构stat{}和常量。</font></i>
<a name='L8'><font color='darkred'>#include</font> <<a href='28.html'>errno.h</a>> <i><font color='green'>// 错误号头文件。包含系统中各种出错号。(Linus 从minix 中引进的)。</font></i>
<a name='L9'><font color='darkred'>#include</font> <<a href='45.html'>sys/types.h</a>> <i><font color='green'>// 类型头文件。定义了基本的系统数据类型。</font></i>
<a name='L10'>
<a name='L11'><font color='darkred'>#include</font> <<a href='34.html'>linux/kernel.h</a>> <i><font color='green'>// 内核头文件。含有一些内核常用函数的原形定义。</font></i>
<a name='L12'><font color='darkred'>#include</font> <<a href='36.html'>linux/sched.h</a>> <i><font color='green'>// 调度程序头文件，定义了任务结构task_struct、初始任务0 的数据，</font></i>
<a name='L13'><i><font color='green'>// 还有一些有关描述符参数设置和获取的嵌入式汇编函数宏语句。</font></i>
<a name='L14'><font color='darkred'>#include</font> <<a href='24.html'>asm/segment.h</a>> <i><font color='green'>// 段操作头文件。定义了有关段寄存器操作的嵌入式汇编函数。</font></i>
<a name='L15'>
<a name='L16'><i><font color='green'>// 字符设备读写函数。</font></i>
<a name='L17'><b>extern</b> <b>int</b> rw_char (<b>int</b> rw, <b>int</b> dev, <b>char</b> *buf, <b>int</b> count, <a href='../S/45.html#L32' title='Defined at 32 in include/sys/types.h.'>off_t</a> * pos);
<a name='L18'><i><font color='green'>// 读管道操作函数。</font></i>
<a name='L19'><b>extern</b> <b>int</b> <a href='../S/16.html#L18' title='Defined at 18 in fs/pipe.c.'>read_pipe</a> (<b>struct</b> m_inode *inode, <b>char</b> *buf, <b>int</b> count);
<a name='L20'><i><font color='green'>// 写管道操作函数。</font></i>
<a name='L21'><b>extern</b> <b>int</b> <a href='../S/16.html#L60' title='Defined at 60 in fs/pipe.c.'>write_pipe</a> (<b>struct</b> m_inode *inode, <b>char</b> *buf, <b>int</b> count);
<a name='L22'><i><font color='green'>// 块设备读操作函数。</font></i>
<a name='L23'><b>extern</b> <b>int</b> <a href='../S/5.html#L70' title='Defined at 70 in fs/block_dev.c.'>block_read</a> (<b>int</b> dev, <a href='../S/45.html#L32' title='Defined at 32 in include/sys/types.h.'>off_t</a> * pos, <b>char</b> *buf, <b>int</b> count);
<a name='L24'><i><font color='green'>// 块设备写操作函数。</font></i>
<a name='L25'><b>extern</b> <b>int</b> <a href='../S/5.html#L23' title='Defined at 23 in fs/block_dev.c.'>block_write</a> (<b>int</b> dev, <a href='../S/45.html#L32' title='Defined at 32 in include/sys/types.h.'>off_t</a> * pos, <b>char</b> *buf, <b>int</b> count);
<a name='L26'><i><font color='green'>// 读文件操作函数。</font></i>
<a name='L27'><b>extern</b> <b>int</b> <a href='../S/10.html#L22' title='Defined at 22 in fs/file_dev.c.'>file_read</a> (<b>struct</b> m_inode *inode, <b>struct</b> file *filp,
<a name='L28'> <b>char</b> *buf, <b>int</b> count);
<a name='L29'><i><font color='green'>// 写文件操作函数。</font></i>
<a name='L30'><b>extern</b> <b>int</b> <a href='../S/10.html#L75' title='Defined at 75 in fs/file_dev.c.'>file_write</a> (<b>struct</b> m_inode *inode, <b>struct</b> file *filp,
<a name='L31'> <b>char</b> *buf, <b>int</b> count);
<a name='L32'>
<a name='L33'><i><font color='green'>//// 重定位文件读写指针系统调用函数。</font></i>
<a name='L34'><i><font color='green'>// 参数fd 是文件句柄，offset 是新的文件读写指针偏移值，origin 是偏移的起始位置，是SEEK_SET</font></i>
<a name='L35'><i><font color='green'>// (0，从文件开始处)、SEEK_CUR(1，从当前读写位置)、SEEK_END(2，从文件尾处)三者之一。</font></i>
<a name='L36'><b>int</b>
<a name='L37'><a href='../R/657.html' title='Multiple refered from 2 places.'>sys_lseek</a> (<b>unsigned</b> <b>int</b> fd, <a href='../S/45.html#L32' title='Defined at 32 in include/sys/types.h.'>off_t</a> offset, <b>int</b> origin)
<a name='L38'><font color='red'>{</font>
<a name='L39'> <b>struct</b> file *file;
<a name='L40'> <b>int</b> tmp;
<a name='L41'>
<a name='L42'><i><font color='green'>// 如果文件句柄值大于程序最多打开文件数NR_OPEN(20)，或者该句柄的文件结构指针为空，或者</font></i>
<a name='L43'><i><font color='green'>// 对应文件结构的i 节点字段为空，或者指定设备文件指针是不可定位的，则返回出错码并退出。</font></i>
<a name='L44'> <b>if</b> (fd >= <a href='../S/31.html#L59' title='Defined at 59 in include/linux/fs.h.'>NR_OPEN</a> || !(file = current->filp[fd]) || !(file->f_inode)
<a name='L45'> || !<a href='../S/31.html#L40' title='Defined at 40 in include/linux/fs.h.'>IS_SEEKABLE</a> (<a href='../S/31.html#L49' title='Defined at 49 in include/linux/fs.h.'>MAJOR</a> (file->f_inode->i_dev)))
<a name='L46'> <b>return</b> -<a href='../S/28.html#L38' title='Defined at 38 in include/errno.h.'>EBADF</a>;
<a name='L47'><i><font color='green'>// 如果文件对应的i 节点是管道节点，则返回出错码，退出。管道头尾指针不可随意移动！</font></i>
<a name='L48'> <b>if</b> (file->f_inode->i_pipe)
<a name='L49'> <b>return</b> -<a href='../S/28.html#L58' title='Defined at 58 in include/errno.h.'>ESPIPE</a>;
<a name='L50'><i><font color='green'>// 根据设置的定位标志，分别重新定位文件读写指针。</font></i>
<a name='L51'> <b>switch</b> (origin)
<a name='L52'> <font color='red'>{</font>
<a name='L53'><i><font color='green'>// origin = SEEK_SET，要求以文件起始处作为原点设置文件读写指针。若偏移值小于零，则出错返</font></i>
<a name='L54'><i><font color='green'>// 回错误码。否则设置文件读写指针等于offset。</font></i>
<a name='L55'> <b>case</b> 0:
<a name='L56'> <b>if</b> (offset < 0)
<a name='L57'> <b>return</b> -<a href='../S/28.html#L51' title='Defined at 51 in include/errno.h.'>EINVAL</a>;
<a name='L58'> file->f_pos = offset;
<a name='L59'> <b>break</b>;
<a name='L60'><i><font color='green'>// origin = SEEK_CUR，要求以文件当前读写指针处作为原点重定位读写指针。如果文件当前指针加</font></i>
<a name='L61'><i><font color='green'>// 上偏移值小于0，则返回出错码退出。否则在当前读写指针上加上偏移值。</font></i>
<a name='L62'> <b>case</b> 1:
<a name='L63'> <b>if</b> (file->f_pos + offset < 0)
<a name='L64'> <b>return</b> -<a href='../S/28.html#L51' title='Defined at 51 in include/errno.h.'>EINVAL</a>;
<a name='L65'> file->f_pos += offset;
<a name='L66'> <b>break</b>;
<a name='L67'><i><font color='green'>// origin = SEEK_END，要求以文件末尾作为原点重定位读写指针。此时若文件大小加上偏移值小于零</font></i>
<a name='L68'><i><font color='green'>// 则返回出错码退出。否则重定位读写指针为文件长度加上偏移值。</font></i>
<a name='L69'> <b>case</b> 2:
<a name='L70'> <b>if</b> ((tmp = file->f_inode->i_size + offset) < 0)
<a name='L71'> <b>return</b> -<a href='../S/28.html#L51' title='Defined at 51 in include/errno.h.'>EINVAL</a>;
<a name='L72'> file->f_pos = tmp;
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