CODEWITHSUNDEEP
socketsnetwork-programminglinux-kernel
Chaitanya H
Chaitanya H

Reputation: 23

Why are there ioctl calls in socket.c?

Trying to understand why there are ioctl calls in socket.c ? I can see a modified kernel that I am using, it has some ioctl calls which load in the required modules when the calls are made.

I was wondering why these calls ended up in socket.c ? Isn't socket kind of not-a-device and ioctls are primarily used for device.

Talking about 2.6.32.0 heavily modified kernel here.

Upvotes: 1

Views: 1748

Answers (1)

Ahmed Masud
Ahmed Masud

Reputation: 22372

ioctl suffers from its historic name. While originally developed to perform i/o controls on devices, it has a generic enough construct that it may be used for arbitrary service requests to the kernel in context of a file descriptor. A file descriptor is an opaque value (just an int) provided by the kernel that can be associated with anything.

Now if you treat a file descriptor and think of things as files, which most *nix constructs do, open/read/write/close isn't enough. What if you want to label a file (rename)? what if you want to wait for a file to become available (ioctl)? what if you want to terminate everything if a file closes (termios)? all the "meta" operations that don't make sense in the core read/write context are lumped under ioctls; fctls; etc. unless they are so frequently used that they deserve their own system call (e.g. flock(2) functionality in BSD4.2)

Upvotes: 2

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