From a8fc92778080c845eaadc369a0ecf5699a03bef0 Mon Sep 17 00:00:00 2001 From: Pavel Emelyanov Date: Thu, 1 Nov 2012 02:01:48 +0000 Subject: sk-filter: Add ability to get socket filter program (v2) The SO_ATTACH_FILTER option is set only. I propose to add the get ability by using SO_ATTACH_FILTER in getsockopt. To be less irritating to eyes the SO_GET_FILTER alias to it is declared. This ability is required by checkpoint-restore project to be able to save full state of a socket. There are two issues with getting filter back. First, kernel modifies the sock_filter->code on filter load, thus in order to return the filter element back to user we have to decode it into user-visible constants. Fortunately the modification in question is interconvertible. Second, the BPF_S_ALU_DIV_K code modifies the command argument k to speed up the run-time division by doing kernel_k = reciprocal(user_k). Bad news is that different user_k may result in same kernel_k, so we can't get the original user_k back. Good news is that we don't have to do it. What we need to is calculate a user2_k so, that reciprocal(user2_k) == reciprocal(user_k) == kernel_k i.e. if it's re-loaded back the compiled again value will be exactly the same as it was. That said, the user2_k can be calculated like this user2_k = reciprocal(kernel_k) with an exception, that if kernel_k == 0, then user2_k == 1. The optlen argument is treated like this -- when zero, kernel returns the amount of sock_fprog elements in filter, otherwise it should be large enough for the sock_fprog array. changes since v1: * Declared SO_GET_FILTER in all arch headers * Added decode of vlan-tag codes Signed-off-by: Pavel Emelyanov Signed-off-by: David S. Miller --- include/uapi/asm-generic/socket.h | 1 + 1 file changed, 1 insertion(+) (limited to 'include/uapi/asm-generic') diff --git a/include/uapi/asm-generic/socket.h b/include/uapi/asm-generic/socket.h index b1bea03274d..2d32d073a6f 100644 --- a/include/uapi/asm-generic/socket.h +++ b/include/uapi/asm-generic/socket.h @@ -43,6 +43,7 @@ /* Socket filtering */ #define SO_ATTACH_FILTER 26 #define SO_DETACH_FILTER 27 +#define SO_GET_FILTER SO_ATTACH_FILTER #define SO_PEERNAME 28 #define SO_TIMESTAMP 29 -- cgit v1.2.3