Linux Device Drivers Development

The llseek method

The llseek function is called when you move the cursor position within a file. The entry point of this method in user space is lseek(). You can refer to the man page in order to print the full description of either method from user space: man llseek and man lseek. Its prototype looks as follows:

loff_t(*llseek) (struct file *filp, loff_t offset, int whence); 

The preceding command is explained as following:

• The return value is the new position in the file.
• loff_t is an offset, relative to the current file position, which defines how much it will be changed.
• whence defines where to seek from. Possible values are:
  • SEEK_SET: This puts the cursor into a position relative to the beginning of the file
  • SEEK_CUR: This puts the ...