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: <20180116144249.308a15d7@gandalf.local.home>
Date:   Tue, 16 Jan 2018 14:42:49 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Vladislav Valtchev <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 21:10:36 +0200
Vladislav Valtchev <vladislav.valtchev@...il.com> wrote:

> On Tue, 2018-01-16 at 12:19 -0500, Steven Rostedt wrote:
> > 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():  
> 
> v3 addresses only the comments for patch 3/3.
> I'm sorry for that. All the other comments will be addressed in v4.
> 
> > 
> > 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  
> 
> Sure, I thought that:
> 
> 	errno = 0;
> 	num = strtol(buf, NULL, 10);
> 
> 	/* strtol() returned 0: we have to check for errors */
> 	if (!num && (errno == EINVAL || errno == ERANGE))
> 		return -1;
> 
> 	if (num > INT_MAX || num < INT_MIN)
> 		return -1;
> 
> covered all the cases because the case:
> (val == LONG_MAX || val == LONG_MIN)
> 
> is covered by: if (num > INT_MAX || num < INT_MIN)
> [no matter the errno]
> 
> but that's not true for 32 bit systems where sizeof(long) == sizeof(int).
> It had to be: if (num >= INT_MAX || num <= INT_MIN), but in that
> case it would exclude two valid int32 values.
> 
> Therefore, let's go with:
> 	if ((errno == ERANGE && (val == LONG_MAX || val == LONG_MIN))
>             || (errno != 0 && val == 0))
> 
> 
> Just let me keep also the following check:
> 
> 	if (num > INT_MAX || num < INT_MIN)
> 		return -1;
> 
> since [INT_MIN, INT_MAX] is a subset of [LONG_MIN, LONG_MAX].
> 

True. What about just doing:


	if (num > INT_MAX || num < INT_MIN || (!num && errno))

That should cover it all, and match what the man pages have.

-- Steve