[sheepdog] [PATCH 3/6] lib: implement wrapper functions for handling EMFILE gracefully

[Liu Yuan]

On Wed, Aug 14, 2013 at 01:27:38AM +0900, Hitoshi Mitake wrote:
> This patch adds wrapper functions of fd creaters for handling EMFILE
> gracefully. When they face EMFILE, they reap unused sockfd and retry
> creating new fds.
> 
> This patch also modifies Makefile of shepherd. Because this patch
> creates a new dependency in libsheepdog, shepherd must linked with
> pthread.
> 
> Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
> ---
>  include/util.h       |  14 +++++++
>  lib/util.c           | 104 +++++++++++++++++++++++++++++++++++++++++++++++++++
>  shepherd/Makefile.am |   2 +-
>  3 files changed, 119 insertions(+), 1 deletion(-)
> 
> diff --git a/include/util.h b/include/util.h
> index ff1f0c7..729037d 100644
> --- a/include/util.h
> +++ b/include/util.h
> @@ -13,6 +13,9 @@
>  #include <sys/eventfd.h>
>  #include <pthread.h>
>  #include <errno.h>
> +#include <sys/types.h>
> +#include <sys/socket.h>
> +#include <fcntl.h>
>  
>  #include "logger.h"
>  #include "list.h"
> @@ -344,4 +347,15 @@ static inline bool is_stdout_console(void)
>  extern mode_t sd_def_fmode;
>  extern mode_t sd_def_dmode;
>  
> +/*
> + * The below x- prefixed wrappers are for handling EMFILE gracefully.
> + * They reap fds of sockfd cache and retry when they face EMFILE.
> + */
> +int xsocket(int domain, int type, int protocol);
> +int xaccept(int sockfd, struct sockaddr *addr, socklen_t *addrlen);
> +int xeventfd(int initval, int flags);
> +int xopen(const char *pathname, int flags, ...);
> +int xtimerfd_create(clockid_t clock_id, int flags);
> +int xepoll_create(int size);
> +
>  #endif
> diff --git a/lib/util.c b/lib/util.c
> index 9781fd8..b88f297 100644
> --- a/lib/util.c
> +++ b/lib/util.c
> @@ -22,8 +22,12 @@
>  #include <signal.h>
>  #include <sys/xattr.h>
>  #include <fcntl.h>
> +#include <stdarg.h>
> +#include <sys/timerfd.h>
> +#include <sys/epoll.h>
>  
>  #include "util.h"
> +#include "sockfd_cache.h"
>  
>  mode_t sd_def_dmode = S_IRUSR | S_IWUSR | S_IXUSR | S_IRGRP | S_IWGRP | S_IXGRP;
>  mode_t sd_def_fmode = S_IRUSR | S_IWUSR | S_IRGRP | S_IWGRP;
> @@ -735,3 +739,103 @@ void list_sort(void *priv, struct list_head *head,
>  
>  	merge_and_restore_back_links(priv, cmp, head, part[max_lev], list);
>  }
> +
> +int xsocket(int domain, int type, int protocol)
> +{
> +	int fd;
> +
> +retry:
> +	fd = socket(domain, type, protocol);
> +	if (fd < 0) {
> +		if (errno == EINTR)
> +			goto retry;
> +
> +		if (errno == EMFILE && sockfd_shrink())
> +			goto retry;
> +	}

I think we should loop until some fds are reclaimed in the sockfd_shrink. After
it returns, it means we have free slots in the sockfd cache.

Thanks
Yuan