LddReadAndWrite < Training2

%SECTION0{LddReadAndWrite}% The read and write system calls

   * read and write data to device

   * return values:
      * = count: the requested amount of bytes were read/written
      * < count: count bytes were read/written (no error!)
      * = 0: read: EOF, write: unspecified (old: equals EAGAIN)
      * < 0: error

   * =stdio= library handles partial reads/writes

   * carefull with userspace pointers!
      * could be unmapped in kernel space
      * could be swapped out
      * could be invalid!


---++API

*read and write file operations:*

<verbatim>
ssize_t read(struct file *filp, char __user *buff, size_t count, loff_t *f_pos);
ssize_t write(struct file *filp, const char __user *buff, size_t count, loff_t *f_pos);
</verbatim>


*userspace access:*

<verbatim>
unsigned long copy_to_user(void __user *to, const void *from, unsigned long count);
unsigned long copy_from_user(void *to, const void __user *from, unsigned long count);
</verbatim>

5.3.4. The open and release methods		1. Denx Training Topics		5.3.6. Non-Blocking IO
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