netdev - Re: [PATCH v2 3/3] lib/string_helpers.c: Change semantics of string_escape

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Date:	Mon, 02 Feb 2015 12:56:37 +0200
From:	Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:	Rasmus Villemoes <linux@...musvillemoes.dk>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Trond Myklebust <trond.myklebust@...marydata.com>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	"David S. Miller" <davem@...emloft.net>,
	linux-kernel@...r.kernel.org, linux-nfs@...r.kernel.org,
	netdev@...r.kernel.org
Subject: Re: [PATCH v2 3/3] lib/string_helpers.c: Change semantics of
 string_escape_mem

On Sat, 2015-01-31 at 00:39 +0100, Rasmus Villemoes wrote:
> On Fri, Jan 30 2015, Andy Shevchenko <andriy.shevchenko@...ux.intel.com> wrote:
> >> >>   * Return:
> >> >> - * The amount of the characters processed to the destination buffer, or
> >> >> - * %-ENOMEM if the size of buffer is not enough to put an escaped character is
> >> >> - * returned.
> >> >> - *
> >> >> - * Even in the case of error @dst pointer will be updated to point to the byte
> >> >> - * after the last processed character.
> >> >> + * The total size of the escaped output that would be generated for
> >> >> + * the given input and flags. To check whether the output was
> >> >> + * truncated, compare the return value to osz. There is room left in
> >> >> + * dst for a '\0' terminator if and only if ret < osz.
> >> >>   */
> >> >> -int string_escape_mem(const char *src, size_t isz, char **dst, size_t osz,
> >> >> -		      unsigned int flags, const char *esc)
> >> >> +size_t string_escape_mem(const char *src, size_t isz, char *dst, size_t osz,
> >> >> +			 unsigned int flags, const char *esc)
> >> >
> >> > I prefer to leave the prototype the same. int for return is okay. dst
> >> > should be updated accordingly.
> >> 
> >> Please explain exactly what you think the return value should be, and
> >> what *dst should be set to.
> >
> > Return value like you proposed, *dst is incremented by it.
> 
> The more I think about it, the less I like having dst being char**.
> 
> (1) It is unlike most other functions taking buffer+size arguments.
> (2) It is inconvenient. Callers doing
> 
>   char escaped[SOME_SIZE];
> 
> or
> 
>   char *escaped = kmalloc(likely_big_enough);
> 
> can't just pass &escaped; they would need to use an extra dummy variable.
> 
> (3) With the return value telling the size of the would-be generated
> output, it is redundant.
> 
> In fact, I dislike it so much that I'm not going to sign off on a patch
> where dst is still char**.

Fair enough, though there usual case when temporary variable is already
present (at least current users).

Let's proceed with char *dst.

-- 
Andy Shevchenko <andriy.shevchenko@...el.com>
Intel Finland Oy

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