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From: Rasmus Villemoes <linux@rasmusvillemoes.dk>
To: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>,
	Trond Myklebust <trond.myklebust@primarydata.com>,
	"J. Bruce Fields" <bfields@fieldses.org>,
	"David S. Miller" <davem@davemloft.net>,
	linux-kernel@vger.kernel.org, linux-nfs@vger.kernel.org,
	netdev@vger.kernel.org
Subject: Re: [PATCH v2 3/3] lib/string_helpers.c: Change semantics of string_escape_mem
Date: Sat, 31 Jan 2015 00:39:22 +0100	[thread overview]
Message-ID: <87pp9vhm8l.fsf@rasmusvillemoes.dk> (raw)
In-Reply-To: <1422613655.31903.351.camel@linux.intel.com> (Andy Shevchenko's message of "Fri, 30 Jan 2015 12:27:35 +0200")

On Fri, Jan 30 2015, Andy Shevchenko <andriy.shevchenko@linux.intel.com> wrote:

> On Thu, 2015-01-29 at 15:29 +0100, Rasmus Villemoes wrote:
>> On Thu, Jan 29 2015, Andy Shevchenko <andriy.shevchenko@linux.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**.

>> > Could it be a part of nomem test still?
>> 
>> What nomem test? string_escape_mem with snprintf-like semantics cannot
>> return an error; that has to be checked by the caller. 
>
> Make this code a separate test, which actually still nomem, since you
> have not enough memory in the destination buffer. What the problem to
> check for proper return value and the last couple of characters written
> to the destination buffer?

Sure, it could go into a separate helper. Anyway, the semantics of
string_escape_mem needs to be decided before it makes sense to update
the tests.

> When your series will be ready (and actually I recommend to push first
> patch apart from the rest since it's not related) 

I agree on that part. Andrew, could you take 1/3
(http://thread.gmane.org/gmane.linux.kernel/1876841/focus=348404), and
then we'll see when the %pE case gets sorted out.

Rasmus

WARNING: multiple messages have this Message-ID
From: Rasmus Villemoes <linux-qQsb+v5E8BnlAoU/VqSP6n9LOBIZ5rWg@public.gmane.org>
To: Andy Shevchenko
	<andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: Andrew Morton
	<akpm-de/tnXTf+JLsfHDXvbKv3WD2FQJk+8+b@public.gmane.org>,
	Trond Myklebust
	<trond.myklebust-7I+n7zu2hftEKMMhf/gKZA@public.gmane.org>,
	"J. Bruce Fields"
	<bfields-uC3wQj2KruNg9hUCZPvPmw@public.gmane.org>,
	"David S. Miller" <davem-fT/PcQaiUtIeIZ0/mPfg9Q@public.gmane.org>,
	linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	netdev-u79uwXL29TY76Z2rM5mHXA@public.gmane.org
Subject: Re: [PATCH v2 3/3] lib/string_helpers.c: Change semantics of string_escape_mem
Date: Sat, 31 Jan 2015 00:39:22 +0100	[thread overview]
Message-ID: <87pp9vhm8l.fsf@rasmusvillemoes.dk> (raw)
In-Reply-To: <1422613655.31903.351.camel-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> (Andy Shevchenko's message of "Fri, 30 Jan 2015 12:27:35 +0200")

On Fri, Jan 30 2015, Andy Shevchenko <andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> wrote:

> On Thu, 2015-01-29 at 15:29 +0100, Rasmus Villemoes wrote:
>> On Thu, Jan 29 2015, Andy Shevchenko <andriy.shevchenko-VuQAYsv1563Yd54FQh9/CA@public.gmane.org> 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**.

>> > Could it be a part of nomem test still?
>> 
>> What nomem test? string_escape_mem with snprintf-like semantics cannot
>> return an error; that has to be checked by the caller. 
>
> Make this code a separate test, which actually still nomem, since you
> have not enough memory in the destination buffer. What the problem to
> check for proper return value and the last couple of characters written
> to the destination buffer?

Sure, it could go into a separate helper. Anyway, the semantics of
string_escape_mem needs to be decided before it makes sense to update
the tests.

> When your series will be ready (and actually I recommend to push first
> patch apart from the rest since it's not related) 

I agree on that part. Andrew, could you take 1/3
(http://thread.gmane.org/gmane.linux.kernel/1876841/focus=348404), and
then we'll see when the %pE case gets sorted out.

Rasmus
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  reply	other threads:[~2015-01-30 23:39 UTC|newest]

Thread overview: 52+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2015-01-28 13:25 [PATCH 0/2] Two printf fixes Rasmus Villemoes
2015-01-28 13:25 ` [PATCH 1/2] lib/vsprintf.c: Fix potential NULL deref in hex_string Rasmus Villemoes
2015-01-28 14:53   ` Andy Shevchenko
2015-01-28 15:49     ` Rasmus Villemoes
2015-01-28 16:43       ` Andy Shevchenko
2015-01-28 13:25 ` [PATCH 2/2] string_helpers: Change semantics of string_escape_mem Rasmus Villemoes
2015-01-28 15:05   ` Andy Shevchenko
2015-01-29 10:03 ` [PATCH v2 0/3] Two printf fixes Rasmus Villemoes
2015-01-29 10:03   ` [PATCH v2 1/3] lib/vsprintf.c: Fix potential NULL deref in hex_string Rasmus Villemoes
2015-01-29 10:43     ` Andy Shevchenko
2015-01-29 10:03   ` [PATCH v2 2/3] lib/string_helpers.c: Refactor string_escape_mem Rasmus Villemoes
2015-01-29 12:12     ` Andy Shevchenko
2015-01-29 13:10       ` Rasmus Villemoes
2015-01-29 13:37         ` Andy Shevchenko
2015-01-29 19:33           ` Jeff Epler
2015-01-30 10:14             ` Andy Shevchenko
2015-01-29 10:03   ` [PATCH v2 3/3] lib/string_helpers.c: Change semantics of string_escape_mem Rasmus Villemoes
2015-01-29 13:29     ` Andy Shevchenko
2015-01-29 14:29       ` Rasmus Villemoes
2015-01-30 10:27         ` Andy Shevchenko
2015-01-30 23:39           ` Rasmus Villemoes [this message]
2015-01-30 23:39             ` Rasmus Villemoes
2015-02-02 10:56             ` Andy Shevchenko
2015-02-09 23:44   ` [PATCH v3 0/3] Two printf fixes Rasmus Villemoes
2015-02-09 23:44     ` Rasmus Villemoes
2015-02-09 23:44     ` [PATCH v3 1/3] lib/vsprintf.c: Fix potential NULL deref in hex_string Rasmus Villemoes
2015-02-09 23:44     ` [PATCH v3 2/3] lib/string_helpers.c: Refactor string_escape_mem Rasmus Villemoes
2015-02-10 12:16       ` Andy Shevchenko
2015-02-09 23:44     ` [PATCH v3 3/3] lib/string_helpers.c: Change semantics of string_escape_mem Rasmus Villemoes
2015-02-09 23:44       ` Rasmus Villemoes
2015-02-10 12:32       ` Andy Shevchenko
2015-02-10 12:32         ` Andy Shevchenko
2015-02-10 13:02         ` Rasmus Villemoes
2015-02-10 14:22           ` Andy Shevchenko
2015-02-10 14:22             ` Andy Shevchenko
2015-02-21  1:35             ` Rasmus Villemoes
2015-02-23 12:50               ` Andy Shevchenko
2015-02-23 12:50                 ` Andy Shevchenko
2015-02-23 22:55                 ` Rasmus Villemoes
2015-02-23 22:55                   ` Rasmus Villemoes
2015-03-02 12:37                   ` Andy Shevchenko
2015-03-02 12:37                     ` Andy Shevchenko
2015-03-02 23:03                     ` Rasmus Villemoes
2015-03-03 10:26                       ` Andy Shevchenko
2015-03-03 10:26                         ` Andy Shevchenko
2015-03-03 23:20     ` [PATCH v4 0/3] Two printf fixes Rasmus Villemoes
2015-03-03 23:20       ` [PATCH v4 1/3] lib/vsprintf.c: Fix potential NULL deref in hex_string Rasmus Villemoes
2015-03-03 23:20       ` [PATCH v4 2/3] lib/string_helpers.c: Refactor string_escape_mem Rasmus Villemoes
2015-03-04 10:51         ` Andy Shevchenko
2015-03-03 23:20       ` [PATCH v4 3/3] lib/string_helpers.c: Change semantics of string_escape_mem Rasmus Villemoes
2015-03-04 11:49         ` Andy Shevchenko
2015-03-04 11:49           ` Andy Shevchenko

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