[CRIU] [PATCH] pie: Optimize send_fds() and recv_fds() with opts

[Pavel Emelyanov]

On 10/27/2016 08:59 PM, Kirill Tkhai wrote:
> Do not ask kernel to transfer more opts than we really need.

Can you write some more details here, please.

> Signed-off-by: Kirill Tkhai <ktkhai at virtuozzo.com>
> ---
>  criu/pie/util-fd.c |    9 +++++----
>  1 file changed, 5 insertions(+), 4 deletions(-)
> 
> diff --git a/criu/pie/util-fd.c b/criu/pie/util-fd.c
> index 51696ee..f3f9c2e 100644
> --- a/criu/pie/util-fd.c
> +++ b/criu/pie/util-fd.c
> @@ -21,7 +21,7 @@
>  
>  #include "common/bug.h"
>  
> -static void scm_fdset_init_chunk(struct scm_fdset *fdset, int nr_fds)
> +static void scm_fdset_init_chunk(struct scm_fdset *fdset, int nr_fds, bool with_flags)
>  {
>  	struct cmsghdr *cmsg;
>  
> @@ -29,6 +29,8 @@ static void scm_fdset_init_chunk(struct scm_fdset *fdset, int nr_fds)
>  
>  	cmsg		= CMSG_FIRSTHDR(&fdset->hdr);
>  	cmsg->cmsg_len	= fdset->hdr.msg_controllen;
> +
> +	fdset->iov.iov_len = with_flags ? (sizeof(struct fd_opts) * nr_fds) : 1;
>  }
>  
>  static int *scm_fdset_init(struct scm_fdset *fdset, struct sockaddr_un *saddr,
> @@ -39,7 +41,6 @@ static int *scm_fdset_init(struct scm_fdset *fdset, struct sockaddr_un *saddr,
>  	BUILD_BUG_ON(sizeof(fdset->msg_buf) < (CMSG_SPACE(sizeof(int) * CR_SCM_MAX_FD)));
>  
>  	fdset->iov.iov_base		= fdset->opts;
> -	fdset->iov.iov_len		= with_flags ? sizeof(fdset->opts) : 1;
>  
>  	fdset->hdr.msg_iov		= &fdset->iov;
>  	fdset->hdr.msg_iovlen		= 1;
> @@ -67,7 +68,7 @@ int send_fds(int sock, struct sockaddr_un *saddr, int len,
>  	cmsg_data = scm_fdset_init(&fdset, saddr, len, with_flags);
>  	for (i = 0; i < nr_fds; i += min_fd) {
>  		min_fd = min(CR_SCM_MAX_FD, nr_fds - i);
> -		scm_fdset_init_chunk(&fdset, min_fd);
> +		scm_fdset_init_chunk(&fdset, min_fd, with_flags);
>  		builtin_memcpy(cmsg_data, &fds[i], sizeof(int) * min_fd);
>  
>  		if (with_flags) {
> @@ -133,7 +134,7 @@ int recv_fds(int sock, int *fds, int nr_fds, struct fd_opts *opts)
>  	cmsg_data = scm_fdset_init(&fdset, NULL, 0, opts != NULL);
>  	for (i = 0; i < nr_fds; i += min_fd) {
>  		min_fd = min(CR_SCM_MAX_FD, nr_fds - i);
> -		scm_fdset_init_chunk(&fdset, min_fd);
> +		scm_fdset_init_chunk(&fdset, min_fd, opts != NULL);
>  
>  		ret = __sys(recvmsg)(sock, &fdset.hdr, 0);
>  		if (ret <= 0)
> 
> .
>