Re: [LTP] [RFC PATCH] tst_checkpoint_signal_child: implemented timeout

[Jan Stancek <jstancek@redhat.com>]

----- Original Message -----
> From: "Stanislav Kholmanskikh" <stanislav.kholmanskikh@oracle.com>
> To: ltp-list@lists.sourceforge.net
> Cc: "vasily isaenko" <vasily.isaenko@oracle.com>
> Sent: Wednesday, 13 November, 2013 8:52:42 AM
> Subject: [LTP] [RFC PATCH] tst_checkpoint_signal_child: implemented timeout
> 
> If a child exits before opening TST_CHECKPOINT_FIFO
> for reading, tst_checkpoint_signal_child() issued from the parent
> will block forever.
> 
> To handle such situations added timeout logic to
> tst_checkpoint_signal_child();
> 
> Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
> ---
>  lib/tst_checkpoint.c |   56
>  ++++++++++++++++++++++++++++++++++++++++++++++++-
>  1 files changed, 54 insertions(+), 2 deletions(-)

Hi,

I would go with just 2 return values:
  -1 - for error/timeout
  fd - otherwise

fd == 0 is a valid descriptor
we can tell if it was timeout or error by errno code 

Why do we need "saved_errno"?

Regards,
Jan

> 
> diff --git a/lib/tst_checkpoint.c b/lib/tst_checkpoint.c
> index 56c86b5..a7936da 100644
> --- a/lib/tst_checkpoint.c
> +++ b/lib/tst_checkpoint.c
> @@ -30,9 +30,54 @@
>  #include <sys/stat.h>
>  #include <fcntl.h>
>  #include <poll.h>
> +#include <time.h>
>  
>  #include "tst_checkpoint.h"
>  
> +/*
> + * Issue open() on 'path' fifo with O_WRONLY flag and wait for
> + * a reader up to 'timeout' ms.
> + *
> + * Returns:
> + *   0   - timeout has happened
> + *   > 0 - file descriptor
> + *   -1  - an error has occurred (errno is set accordingly)
> + *
> + */
> +int open_wronly_timed(const char *path, unsigned int timeout)
> +{
> +	int fd;
> +	int interval_ms = 1; /* how often issue open(O_NONBLOCK) */
> +	long timeleft = timeout;
> +	int saved_errno = errno;
> +
> +	struct timespec interval;
> +	interval.tv_sec = 0;
> +	interval.tv_nsec = interval_ms * 1000000; /* in ns */
> +
> +	for (;;) {
> +		fd = open(path, O_WRONLY | O_NONBLOCK);
> +		if (fd < 0) {
> +			if ((errno == ENXIO) || (errno == EINTR)) {
> +				if (timeleft <= 0) {
> +					errno = saved_errno;
> +
> +				return 0;
> +				}
> +
> +				timeleft -= interval_ms;
> +				nanosleep(&interval, NULL);
> +
> +				continue;
> +			}
> +
> +			return -1;
> +		}
> +
> +		return fd;
> +	}
> +}
> +
>  void tst_checkpoint_init(const char *file, const int lineno,
>                           struct tst_checkpoint *self)
>  {
> @@ -195,12 +240,19 @@ void tst_checkpoint_signal_child(const char *file,
> const int lineno,
>  {
>  	int ret, fd;
>  	
> -	fd = open(TST_CHECKPOINT_FIFO, O_WRONLY);
> +	fd = open_wronly_timed(TST_CHECKPOINT_FIFO, self->timeout);
>  
> -	if (fd < 0) {
> +	switch (fd) {
> +	case 0:
> +		tst_brkm(TBROK, cleanup_fn,
> +			"Checkpoint timeouted after %u msecs at %s:%d",
> +			self->timeout, file, lineno);
> +	break;
> +	case -1:
>  		tst_brkm(TBROK | TERRNO, cleanup_fn,
>  		         "Failed to open fifo '%s' at %s:%d",
>  		         TST_CHECKPOINT_FIFO, file, lineno);
> +	break;
>  	}
>  
>  	ret = write(fd, "p", 1);
> --
> 1.7.1
> 
> 
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