linux-kernel - Re: [PATCH v3 1/3] trace-cmd: Make read_proc() to return int status via OUT arg

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Message-ID: <20180116121913.42d09aea@gandalf.local.home>
Date:   Tue, 16 Jan 2018 12:19:13 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     "Vladislav Valtchev (VMware)" <vladislav.valtchev@...il.com>
Cc:     linux-trace-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
        y.karadz@...il.com
Subject: Re: [PATCH v3 1/3] trace-cmd: Make read_proc() to return int status
 via OUT arg

On Tue, 16 Jan 2018 09:47:42 +0200
"Vladislav Valtchev (VMware)" <vladislav.valtchev@...il.com> wrote:

> +	errno = 0;
> +
> +	/* Read an integer from buf ignoring any non-digit trailing characters. */
> +	num = strtol(buf, NULL, 10);
> +
> +	/* strtol() returned 0: we have to check for errors */
> +	if (!num && (errno == EINVAL || errno == ERANGE))
> +		return -1;

Repeating again here. According to the man page of strtol():

RETURN VALUE
       The  strtol() function returns the result of the conversion, unless the
       value would underflow or overflow.  If an  underflow  occurs,  strtol()
       returns  LONG_MIN.   If  an overflow occurs, strtol() returns LONG_MAX.
       In both cases, errno is set to ERANGE.  Precisely the  same  holds  for
       strtoll()  (with  LLONG_MIN  and  LLONG_MAX  instead  of  LONG_MIN  and
       LONG_MAX).

and this:

       The implementation may also set errno to EINVAL in case  no  conversion
       was performed (no digits seen, and 0 returned).

Thus, !num is not enough. The example in the man page has:

           errno = 0;    /* To distinguish success/failure after call */
           val = strtol(str, &endptr, base);

           /* Check for various possible errors */

           if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN))
                   || (errno != 0 && val == 0)) {
               perror("strtol");
               exit(EXIT_FAILURE);
           }

Let's follow this.

-- Steve