From: Nguyen Thai Ngoc Duy <pclouds@gmail.com>
Date: Wed, 27 Apr 2011 00:12:53 GMT
Subject: Re: [PATCH] strbuf: allocate enough space when strbuf_setlen() is called first time
Message-ID: <BANLkTi=vqgWgS2D2cD3Qwk1Z7_jqLarR3g@mail.gmail.com>
In-Reply-To: <4DB738A1.8020706@lsrfire.ath.cx>

2011/4/27 René Scharfe <rene.scharfe@lsrfire.ath.cx>:
> Am 26.04.2011 19:18, schrieb Junio C Hamano:
>> Nguyễn Thái Ngọc Duy<pclouds@gmail.com>  writes:
>>
>>> strbuf_grow(sb, 0) may allocate less than requested len and violate the
>>> next assertion.
>>>
>>> Signed-off-by: Nguyễn Thái Ngọc Duy<pclouds@gmail.com>
>>> ---
>>>   strbuf.h |    2 +-
>>>   1 files changed, 1 insertions(+), 1 deletions(-)
>>>
>>> diff --git a/strbuf.h b/strbuf.h
>>> index 07060ce..ab213da 100644
>>> --- a/strbuf.h
>>> +++ b/strbuf.h
>>> @@ -34,7 +34,7 @@ extern void strbuf_grow(struct strbuf *, size_t);
>>>
>>>   static inline void strbuf_setlen(struct strbuf *sb, size_t len) {
>>>      if (!sb->alloc)
>>> -            strbuf_grow(sb, 0);
>>> +            strbuf_grow(sb, len);
>>>      assert(len<  sb->alloc);
>>
>> Wait.  Isn't _setlen() meant to be used only to truncate at the length,
>> and isn't that clearly documented?
>>
>> I don't think we need this patch at all.
>
> How about something like this instead?  The call to strbuf_grow() was
> introduced in a8f3e2219 when there was no strbuf_slopbuf buffer that
> nowadays makes sure we always have a place to write an initial NUL.
> We can take it out again now, simplifying the code and hopefully
> avoiding future confusion.
>
>  strbuf.h |    4 +---
>  1 files changed, 1 insertions(+), 3 deletions(-)
>
> diff --git a/strbuf.h b/strbuf.h
> index 07060ce..b157ede 100644
> --- a/strbuf.h
> +++ b/strbuf.h
> @@ -33,9 +33,7 @@ static inline size_t strbuf_avail(const struct strbuf *sb) {
>  extern void strbuf_grow(struct strbuf *, size_t);
>
>  static inline void strbuf_setlen(struct strbuf *sb, size_t len) {
> -       if (!sb->alloc)
> -               strbuf_grow(sb, 0);
> -       assert(len < sb->alloc);
> +       assert(len < (sb->alloc ? sb->alloc : 1));
>        sb->len = len;
>        sb->buf[len] = '\0';
>  }
>
>

Fine to me. I forgot the document, saw _grow and was under impression
that _setlen can grow too.
-- 
Duy