Re: [Xen-devel] [PATCH 3/6] libxl: events: Deregister, don't just modify, sigchld pipe fd

[Ian Campbell <Ian.Campbell@xxxxxxxxxx>]

On Thu, 2014-11-27 at 18:27 +0000, Ian Jackson wrote:
> We want to have no fd events registered when we are idle.  This
> implies that we must be able to deregister our interest in the sigchld
> self-pipe fd, not just modify to request no events.
> 
> Signed-off-by: Ian Jackson <Ian.Jackson@xxxxxxxxxxxxx>

Acked-by: Ian Campbell <ian.campbell@xxxxxxxxxx>

I think in principal there is now some redundant code in
libxl__sigchld_needed which calls modify to set POLLIN if the fd is not
registered. I think it's redundant because now the fd is registered iff
it is looking for POLLIN.

> ---
>  tools/libxl/libxl_fork.c |    9 +--------
>  1 file changed, 1 insertion(+), 8 deletions(-)
> 
> diff --git a/tools/libxl/libxl_fork.c b/tools/libxl/libxl_fork.c
> index fa15095..144208a 100644
> --- a/tools/libxl/libxl_fork.c
> +++ b/tools/libxl/libxl_fork.c
> @@ -372,15 +372,8 @@ static void sigchld_user_remove(libxl_ctx *ctx) /* 
> idempotent */
>  
>  void libxl__sigchld_notneeded(libxl__gc *gc) /* non-reentrant, idempotent */
>  {
> -    int rc;
> -
>      sigchld_user_remove(CTX);
> -
> -    if (libxl__ev_fd_isregistered(&CTX->sigchld_selfpipe_efd)) {
> -        rc = libxl__ev_fd_modify(gc, &CTX->sigchld_selfpipe_efd, 0);
> -        if (rc)
> -            libxl__ev_fd_deregister(gc, &CTX->sigchld_selfpipe_efd);
> -    }
> +    libxl__ev_fd_deregister(gc, &CTX->sigchld_selfpipe_efd);
>  }
>  
>  int libxl__sigchld_needed(libxl__gc *gc) /* non-reentrant, idempotent */



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