[libvirt] [PATCH 4/8] process: Translate "unlimited" correctly

[Luiz Capitulino]

On Thu, 23 Mar 2017 19:16:43 +0100
Andrea Bolognani <abologna at redhat.com> wrote:

> The value we use internally to represent the lack of a memory
> locking limit, VIR_DOMAIN_MEMORY_PARAM_UNLIMITED, doesn't
> match the value setrlimit() and prlimit() use for the same
> purpose, RLIM_INFINITY, so we have to handle the translation
> ourselves.
> ---
>  src/util/virprocess.c | 20 +++++++++++++++++---
>  1 file changed, 17 insertions(+), 3 deletions(-)
> 
> diff --git a/src/util/virprocess.c b/src/util/virprocess.c
> index 16eb412..1fbbbb3 100644
> --- a/src/util/virprocess.c
> +++ b/src/util/virprocess.c
> @@ -747,7 +747,15 @@ virProcessSetMaxMemLock(pid_t pid, unsigned long long bytes)
>      if (bytes == 0)
>          return 0;
>  
> -    rlim.rlim_cur = rlim.rlim_max = bytes;
> +    /* We use VIR_DOMAIN_MEMORY_PARAM_UNLIMITED internally to represent
> +     * unlimited memory amounts, but setrlimit() and prlimit() use
> +     * RLIM_INFINITY for the same purpose, so we need to translate between
> +     * the two conventions */
> +    if (virMemoryLimitIsSet(bytes))
> +        rlim.rlim_cur = rlim.rlim_max = bytes;
> +    else
> +        rlim.rlim_cur = rlim.rlim_max = RLIM_INFINITY;

I know I'm not very smart, but I had trouble parsing this. What
about:

if (virMemoryLimitIsInfinity(bytes))
	rlim.rlim_cur = rlim.rlim_max = RLIM_INFINITY;
...

This reads better, and avoids using virMemoryLimitIsSet() which
seems very error-prone. It doesn't check for zero and it's strange
that "limit < infinity" means "limit is set".

> +
>      if (pid == 0) {
>          if (setrlimit(RLIMIT_MEMLOCK, &rlim) < 0) {
>              virReportSystemError(errno,
> @@ -810,8 +818,14 @@ virProcessGetMaxMemLock(pid_t pid,
>      }
>  
>      /* virProcessSetMaxMemLock() sets both rlim_cur and rlim_max to the
> -     * same value, so we can retrieve just rlim_max here */
> -    *bytes = rlim.rlim_max;
> +     * same value, so we can retrieve just rlim_max here. We use
> +     * VIR_DOMAIN_MEMORY_PARAM_UNLIMITED internally to represent unlimited
> +     * memory amounts, but setrlimit() and prlimit() use RLIM_INFINITY for the
> +     * same purpose, so we need to translate between the two conventions */
> +    if (rlim.rlim_max == RLIM_INFINITY)
> +        *bytes = VIR_DOMAIN_MEMORY_PARAM_UNLIMITED;
> +    else
> +        *bytes = rlim.rlim_max;
>  
>      return 0;
>  }