[CRIU] [PATCH 1/7] util: new string helpers introduced

[Pavel Emelyanov]

On 12/16/2015 06:33 PM, Stanislav Kinsburskiy wrote:
> This patch brings add_to_string() and construct_string() helpers.
> They allow to create a string with variable amount of parameters in sprintf()
> manner, but supporting string allocation (and reallocation if necessary)
> 
> Signed-off-by: Stanislav Kinsburskiy <skinsbursky at virtuozzo.com>
> ---
>  include/util.h |    4 ++++
>  util.c         |   61 ++++++++++++++++++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 65 insertions(+)
> 
> diff --git a/include/util.h b/include/util.h
> index df708c8..5030065 100644
> --- a/include/util.h
> +++ b/include/util.h
> @@ -275,4 +275,8 @@ void tcp_nodelay(int sk, bool on);
>  void tcp_cork(int sk, bool on);
>  
>  const char *ns_to_string(unsigned int ns);
> +
> +char *add_to_string(char *str, const char *fmt, ...);
> +char *construct_string(const char *fmt, ...);
> +
>  #endif /* __CR_UTIL_H__ */
> diff --git a/util.c b/util.c
> index d56f973..a27b0b6 100644
> --- a/util.c
> +++ b/util.c
> @@ -51,6 +51,67 @@
>  
>  #define VMA_OPT_LEN	128
>  
> +static char *add_to_string_vargs(char *str, const char *fmt, va_list args)
> +{
> +	size_t offset = 0, delta;
> +	int ret;
> +	char *new;
> +	va_list tmp;
> +
> +	if (str)
> +		offset = strlen(str);
> +	delta = strlen(fmt) * 2;
> +
> +	do {
> +		ret = -ENOMEM;
> +		new = xrealloc(str, offset + delta);
> +		if (new) {
> +			va_copy(tmp, args);
> +			ret = vsnprintf(new + offset, delta, fmt, tmp);
> +			if (ret >= delta) {
> +				delta = ret +1;

Please, don't fight for every single byte. Calling construct_string("%d", 1234567890)
would result in 6 realloc-s and va_copy-s.

> +				str = new;
> +				ret = 0;
> +			}
> +		}
> +	} while (ret == 0);
> +
> +	if (ret == -ENOMEM) {
> +		/* realloc failed. We must release former string */
> +		pr_err("Failed to allocate string\n");
> +		xfree(str);
> +	} else if (ret < 0) {
> +		/* vsnprintf failed */
> +		pr_err("Failed to print string\n");
> +		xfree(new);
> +		new = NULL;
> +	}
> +	return new;
> +}
> +
> +char *add_to_string(char *str, const char *fmt, ...)
> +{
> +	va_list args;
> +
> +	va_start(args, fmt);
> +	str = add_to_string_vargs(str, fmt, args);
> +	va_end(args);
> +
> +	return str;
> +}
> +
> +char *construct_string(const char *fmt, ...)
> +{
> +	va_list args;
> +	char *str;
> +
> +	va_start(args, fmt);
> +	str = add_to_string_vargs(NULL, fmt, args);
> +	va_end(args);
> +
> +	return str;
> +}
> +
>  static void vma_opt_str(const struct vma_area *v, char *opt)
>  {
>  	int p = 0;
> 
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