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

[Stanislav Kinsburskiу]

16 дек. 2015 г. 9:27 PM пользователь Stanislav Kinsburskiy <skinsbursky at odin.com> написал:
>
>
>
> 16.12.2015 21:21, Stanislav Kinsburskiy пишет: 
> > 
> > 
> > 16.12.2015 18:41, Pavel Emelyanov пишет: 
> >> 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. 
> > 
> > I think, you are mistaken. This "+1" is not a fight for 1 byte. 
> > 
> > From man page of vsnprintf: 
> > "The functions ... vsnprintf() ...  If the output was truncated ... 
> > _return  number  of  characters_ (excluding  the  terminating null 
> > byte) which _would have been written_ to the final string if enough 
> > space had been available. " 
> > 
> > IOW, vsnprintf returns the amount of space to allocate. And "+1" is 
> > the space for '\0', which was excluded from the result. 
> > Thus, only two call for va_copy and realloc will happen for any string. 
> > This can be optimed a bit by calling first realloc with, say, 32 
> > bytes. But I though, that it doesn't make much sense. 
> > 
>
> Sorry. I forgot my own code. 
> Initial allocation is done for strlen(str) * 2. 

strlen(fmt) * 2, of course...

> If it's not enought, then result of vsnprintf() is used to allocate a 
> string of sufficient size. 
>
> >>> +                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; 
> >>> 
> >>> _______________________________________________ 
> >>> CRIU mailing list 
> >>> CRIU at openvz.org 
> >>> https://lists.openvz.org/mailman/listinfo/criu 
> >>> . 
> >>> 
> > 
>