Why alloc_super use a static variable default_op?
the static struct super_operations default_op is just all zeros, and
just referenced as the initial value of a new allocated super_block,
what does it for?
the filesystem dependent code such as ext2_fill_super would fill this
field eventually,
and after carefully checked, it seems no one filesystem would need a
all zero default_op,
as the command output in the kernel source tree:
$ grep -RInw s_op fs/
You could check all the use of s_op.
/**
* alloc_super - create new superblock
* @type: filesystem type superblock should belong to
*
* Allocates and initializes a new &struct super_block. alloc_super()
* returns a pointer new superblock or %NULL if allocation had failed.
*/
static struct super_block *alloc_super(struct file_system_type *type)
{
struct super_block *s = kzalloc(sizeof(struct super_block), GFP_USER);
static struct super_operations default_op;
if (s) {
...
s->s_op = &default_op;
s->s_time_gran = 1000000000;
}
out:
return s;
}
--
Denis Cheng
Linux Application Developer
"One of my most productive days was throwing away 1000 lines of code."
- Ken Thompson.
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