linux-kernel - Re: [PATCH v2 2/3] string: provide strscpy()

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Message-ID: <CAMuHMdXJRD6wC5WsJOfyoFO5J_AyX+ifT6+6h6JXt-ZFpbjFGw@mail.gmail.com>
Date:	Wed, 8 Jul 2015 22:54:00 +0200
From:	Geert Uytterhoeven <geert@...ux-m68k.org>
To:	Chris Metcalf <cmetcalf@...hip.com>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Al Viro <viro@...iv.linux.org.uk>,
	Fabian Frederick <fabf@...net.be>,
	Randy Dunlap <rdunlap@...radead.org>,
	Rickard Strandqvist <rickard_strandqvist@...ctrumdigital.se>,
	Greg KH <gregkh@...uxfoundation.org>,
	Peter Zijlstra <peterz@...radead.org>,
	"David S. Miller" <davem@...emloft.net>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Sam Ravnborg <sam@...nborg.org>,
	Stephen Rothwell <sfr@...b.auug.org.au>,
	"Theodore Ts'o" <tytso@....edu>,
	Grant Likely <grant.likely@...aro.org>,
	Dan Carpenter <dan.carpenter@...cle.com>,
	Michael Ellerman <mpe@...erman.id.au>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linux-Arch <linux-arch@...r.kernel.org>
Subject: Re: [PATCH v2 2/3] string: provide strscpy()

Hi Chris,

On Wed, Jul 8, 2015 at 10:20 PM, Chris Metcalf <cmetcalf@...hip.com> wrote:
> + * strscpy - Copy a C-string into a sized buffer
> + * @dest: Where to copy the string to
> + * @src: Where to copy the string from
> + * @count: Size of destination buffer
> + *
> + * Copy the string, or as much of it as fits, into the dest buffer.
> + * The routine returns the number of characters copied (not including
> + * the trailing NUL) or -E2BIG if the destination buffer wasn't big enough.
> + * The behavior is undefined if the string buffers overlap.
> + * If the destination buffer isn't big enough, it is NUL terminated.

... unless count is zero

and it's also NUL terminated if it is big enough ;-)

Perhaps
"The destination buffer is always NUL terminated, unless it's zero-sized."

> + *
> + * Preferred to strlcpy() since the API doesn't require reading memory
> + * from the src string beyond the specified "count" bytes, and since
> + * the return value is easier to error-check than strlcpy()'s.
> + * In addition, the implementation is robust to the string changing out
> + * from underneath it, unlike the current strlcpy() implementation.
> + *
> + * Preferred to strncpy() since it always returns a valid string, and
> + * doesn't unnecessarily force the tail of the destination buffer to be
> + * zeroed.  If the zeroing is desired, it's likely cleaner to use strscpy()
> + * with an overflow test, then just memset() the tail of the dest buffer.
> + */
> +ssize_t strscpy(char *dest, const char *src, size_t count)
> +{
> +       const struct word_at_a_time constants = WORD_AT_A_TIME_CONSTANTS;
> +       size_t max = count;
> +       long res = 0;
> +
> +       if (count == 0)
> +               return -E2BIG;

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds
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