sockfd_lookup(9)

🌸 NAME 🌸

okay so bestie, this is sockfd_lookup(9) from the Kernel API Manual, and it's literally the glow-up that takes you from a file number to its socket slot. iconic behavior, no cap.

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✨ SYNOPSIS ✨

struct socket * sockfd_lookup (int fd , int *err );

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🫶 ARGUMENTS 🫶

• fd — the file handle, bestie. that's the starting point.
• err — a pointer where an error code gets returned. it's giving "leave a note if things go sideways" energy.

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💖 DESCRIPTION 💖

so here's the tea: the file handle you pass in gets locked, and the socket it's bound to is returned to you. slay.

if an error happens, the err pointer gets overwritten with a negative errno code, and you get NULL back. that's the vibe check failing, fr fr.

the function is out here checking for both invalid handles and passing a handle which is not a socket. it's not letting impostors through. 💅

on success, the socket object pointer is returned. periodt. ✨

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🦋 SEE ALSO 🦋

also mentions the Kernel file ./net/socket.c, plus this whole friend group of kernel icons:

• move_addr_to_kernel(9)
• move_addr_to_user(9)
• sock_read_xattr(9)
• sock_alloc_file(9)
• sock_from_file(9)
• sock_alloc(9)
• sock_release(9)
• sock_sendmsg(9)
• kernel_sendmsg(9)
• sock_recvmsg(9)
• kernel_recvmsg(9)
• sock_create_lite(9)
• __sock_create(9)
• sock_create(9)
• sock_create_kern(9)
• sock_register(9)
• sock_unregister(9)
• kernel_bind(9)
• kernel_listen(9)
• kernel_accept(9)
• kernel_connect(9)
• kernel_getsockname(9)
• kernel_getpeername(9)
• kernel_sock_shutdown(9)
• kernel_sock_ip_overhead(9)

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xoxo, your kernel bestie 💖 — from source/version ./net, dated October 2026 ✨