bpf: Document optval > PAGE_SIZE behavior for sockopt hooks (8030e250) · Commits · 戴 / test

Extend existing doc with more details about requiring ctx->optlen = 0 for handling optval > PAGE_SIZE. Signed-off-by:

Documentation/bpf/prog_cgroup_sockopt.rst

+14 −0

Original line number	Diff line number	Diff line
		@@ -86,6 +86,20 @@ then the next program in the chain (A) will see those changes,
		not the original input ``setsockopt`` arguments. The potentially
		modified values will be then passed down to the kernel.

		Large optval
		============
		When the ``optval`` is greater than the ``PAGE_SIZE``, the BPF program
		can access only the first ``PAGE_SIZE`` of that data. So it has to options:

		* Set ``optlen`` to zero, which indicates that the kernel should
		use the original buffer from the userspace. Any modifications
		done by the BPF program to the ``optval`` are ignored.
		* Set ``optlen`` to the value less than ``PAGE_SIZE``, which
		indicates that the kernel should use BPF's trimmed ``optval``.

		When the BPF program returns with the ``optlen`` greater than
		``PAGE_SIZE``, the userspace will receive ``EFAULT`` errno.

		Example
		=======