[CRIU] Re: [PATCH 3/6] util-net: Add declaration of scm_fdset structure

[Pavel Emelyanov]

On 03/21/2012 11:47 AM, Cyrill Gorcunov wrote:
> This structure will serve for multiple fds
> transmission/receive.
> 
> Signed-off-by: Cyrill Gorcunov <gorcunov at openvz.org>
> ---
>  include/util-net.h |   21 +++++++++++++++++++++
>  1 files changed, 21 insertions(+), 0 deletions(-)
> 
> diff --git a/include/util-net.h b/include/util-net.h
> index c5a8c46..030f518 100644
> --- a/include/util-net.h
> +++ b/include/util-net.h
> @@ -1,6 +1,9 @@
>  #ifndef UTIL_NET_H_
>  #define UTIL_NET_H_
>  
> +#include <sys/socket.h>
> +#include <sys/un.h>
> +
>  #define UNIX_PATH_MAX (sizeof(struct sockaddr_un) - \
>  			(size_t)((struct sockaddr_un *) 0)->sun_path)
>  
> @@ -8,6 +11,24 @@
>  #define SO_PEEK_OFF            42
>  #endif
>  
> +/*
> + * Because kernel do kmalloc for user data passed
> + * in SCM messages, and there is SCM_MAX_FD as a limit
> + * for descriptors passed at once -- we're trying to
> + * eliminate pressue on kernel memory manager and use
> + * predefined known to work well size of the message buffer.
> + */
> +#define CR_SCM_MSG_SIZE		(1024)
> +#define CR_SCM_MAX_FD		(252)

What for 2 constants? Declare one and make the buffer be int[MAX_FD] one.

> +
> +struct scm_fdset {
> +	struct msghdr	hdr;
> +	struct iovec	iov;
> +	char		msg_buf[CR_SCM_MSG_SIZE];
> +	int		__pad;
> +	int		nr_fds;
> +};
> +
>  extern int send_fd(int sock, struct sockaddr_un *saddr, int len, int fd);
>  extern int recv_fd(int sock);
>  #endif