Unlike accept() the new accept4() system call lets the caller specify
flags for the newly accepted socket file descriptor, such as
SOCK_CLOEXEC and SOCK_NONBLOCK.
This commit will add MSG_PEEK support, which allows a package to be
seen without taking it from the buffer, so that a subsequent recv()
without the MSG_PEEK flag can pick it up.
SPDX License Identifiers are a more compact / standardized
way of representing file license information.
See: https://spdx.dev/resources/use/#identifiers
This was done with the `ambr` search and replace tool.
ambr --no-parent-ignore --key-from-file --rep-from-file key.txt rep.txt *
