linux-kernel - Re: [PATCH 1/6] lib/cmdline.c: Add backslash support to kernel commandline parsing.

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Date:   Mon, 25 Sep 2017 20:39:01 +0200
From:   Michal Suchánek <msuchanek@...e.de>
To:     Al Viro <viro@...IV.linux.org.uk>
Cc:     Tamara Diaconita <diaconitatamara@...il.com>,
        Baoquan He <bhe@...hat.com>,
        Kamlakant Patel <kamlakant.patel@...adcom.com>,
        Jonathan Corbet <corbet@....net>,
        Jani Nikula <jani.nikula@...el.com>,
        Mahesh Salgaonkar <mahesh@...ux.vnet.ibm.com>,
        Trond Myklebust <trond.myklebust@...marydata.com>,
        linux-doc@...r.kernel.org, linux-kernel@...r.kernel.org,
        Nicholas Piggin <npiggin@...il.com>,
        Bamvor Jian Zhang <bamvor.zhangjian@...aro.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Paul Mackerras <paulus@...ba.org>,
        Hari Bathini <hbathini@...ux.vnet.ibm.com>,
        Ilya Matveychikov <matvejchikov@...il.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        linuxppc-dev@...ts.ozlabs.org, Ingo Molnar <mingo@...nel.org>
Subject: Re: [PATCH 1/6] lib/cmdline.c: Add backslash support to kernel
 commandline parsing.

On Fri, 15 Sep 2017 19:28:56 +0200
Michal Suchánek <msuchanek@...e.de> wrote:

> On Fri, 15 Sep 2017 18:14:09 +0100
> Al Viro <viro@...IV.linux.org.uk> wrote:
> 
> > On Fri, Sep 15, 2017 at 07:02:46PM +0200, Michal Suchanek wrote:
> >   
> > >  	for (i = 0; args[i]; i++) {
> > > -		if (isspace(args[i]) && !in_quote)
> > > +		if (isspace(args[i]) && !in_quote && !backslash)
> > >  			break;
> > > -		if (equals == 0) {
> > > -			if (args[i] == '=')
> > > -				equals = i;
> > > +
> > > +		if ((equals == 0) && (args[i] == '='))
> > > +			equals = i;
> > > +
> > > +		if (!backslash) {
> > > +			if ((args[i] == '"') || (args[i] ==
> > > '\\')) {
> > > +				if (args[i] == '"')
> > > +					in_quote = !in_quote;
> > > +				if (args[i] == '\\')
> > > +					backslash = 1;
> > > +
> > > +				memmove(args + 1, args, i);
> > > +				args++;
> > > +				i--;
> > > +			}
> > > +		} else {
> > > +			backslash = 0;
> > >  		}
> > > -		if (args[i] == '"')
> > > -			in_quote = !in_quote;
> > >  	}    
> > 
> > ... and that makes for Unidiomatic Work With Strings Award for this
> > September. Using memmove() for string rewrite is almost always bad
> > taste; in this case it's also (as usual) broken.  
> 
> Care to share how it is broken?

Guess not. I will assume it is perfectly fine then. It works perfectly
fine in my testing.

Using memmove for string rewrite is not a matter of taste. It is the
only library function with sane semantics for rewrite of anything. Then
again open-coding it is always an option and maybe in better taste for
some :->

Michal