Linux C Standard I / O - why duplication

Question

Assuming that I understand the stream correctly, I would like to read a few bytes from the open stream FILE, lets talk using fread:

• syscall readwill copy data from the kernel to the user space buffer
• the user space buffer (either allocated by glibc or provided setvbuf...) will be copied to the buffer providedfread

Why is the second step necessary? why can I get a pointer to the user space buffer, which I will decide if I want to store (copy) or not?

Thank,

Answer 1

, . / , . OTOH, / , , .

Answer 2

- , . . api . /. . , , , , - os.