Question

While writing kernel modules/drivers, most of the time some structures are initialized to point to some specific functions. As a beginner in this could someone explain the importance of this.

I saw the struct file_operations while writing the character device driver

Also I found that eventhough the functions are declared they are not implemented always. Could anyone help on that too. For example, in the kernel source: kernel/dma.c, eventhough

static const struct file_operations proc_dma_operations = {
    .open       = proc_dma_open,
    .read       = seq_read,
    .llseek     = seq_lseek,
    .release    = single_release,
};

are defined, only proc_dma_open is implemented.

Answer 1

The functions seq_read, seq_lseek and single_release are declared in the kernel source file linux-3.1.6/include/linux/seq_file.h and defined in the kernel source file linux-3.1.6/fs/seq_file.c. They are probably common to many file operations.