Re: [PATCH openvswitch v2] netlink: Implement & enable memory mapped netlink i/o

[Ben Pfaff <blp@nicira.com>]

On Sat, Nov 30, 2013 at 01:27:33PM +0100, Thomas Graf wrote:
> Based on the initial patch by Cong Wang posted a couple of months
> ago.
> 
> This is the user space counterpart needed for the kernel patch
> '[PATCH net-next 3/8] openvswitch: Enable memory mapped Netlink i/o'
> 
> Allows the kernel to construct Netlink messages on memory mapped
> buffers and thus avoids copying. The functionality is enabled on
> sockets used for unicast traffic.
> 
> Further optimizations are possible by avoiding the copy into the
> ofpbuf after reading.
> 
> Signed-off-by: Thomas Graf <tgraf@redhat.com>

Clang reports:

    ../lib/netlink-socket.c:330:12: error: cast from 'char *' to 'struct nl_mmap_hdr *' increases required alignment from 1 to 4 [-Werror,-Wcast-align]
        return (struct nl_mmap_hdr *)(start + r->head * sock->frame_size);
               ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    ../lib/netlink-socket.c:369:22: error: implicit declaration of function '__ALIGN_KERNEL' is invalid in C99 [-Werror,-Wimplicit-function-declaration]
    -> sock->frame_size)
                         ^
    ../lib/netlink-protocol.h:213:26: note: expanded from macro 'NL_MMAP_HDRLEN'
    #define NL_MMAP_HDRLEN                  NL_MMAP_MSG_ALIGN(sizeof(struct nl_mmap_hdr))
                                            ^
    ../lib/netlink-protocol.h:212:32: note: expanded from macro 'NL_MMAP_MSG_ALIGN'
    #define NL_MMAP_MSG_ALIGN(sz)           __ALIGN_KERNEL(sz, NL_MMAP_MSG_ALIGNMENT)
                                            ^
GCC reports:

    ../lib/netlink-socket.c: In function 'nl_sock_send_mmap':
    ../lib/netlink-socket.c:369:5: error: implicit declaration of function '__ALIGN_KERNEL' [-Werror=implicit-function-declaration]
    cc1: all warnings being treated as errors

Thanks,

Ben.