linux-kernel - Re: [PATCH] tools: libsubcmd: Drop the less hack that was inherited from Git.

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Date:   Thu, 25 Jan 2018 08:24:26 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Arnaldo Carvalho de Melo <acme@...nel.org>
Cc:     Josh Poimboeuf <jpoimboe@...hat.com>, linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>
Subject: Re: [PATCH] tools: libsubcmd: Drop the less hack that was inherited
 from Git.

Thanks.

This was found because gcc 8 appears to be enabling -Wrestrict in -Wall,
so there is a build failure with mainline gcc.

On Thu, Jan 25, 2018 at 05:16:52AM -0300, Arnaldo Carvalho de Melo wrote:
> Em Wed, Jan 24, 2018 at 02:54:11PM -0600, Josh Poimboeuf escreveu:
> > On Tue, Jan 23, 2018 at 07:38:37PM -0500, Arvind Sankar wrote:
> > > We inherited this hack with the original code from the Git project. The
> > > select call is invalid as the two fd_set pointers should not be aliased.
> > > 
> > > We could fix it, but the Git project removed this hack in 2012 in commit
> > > e8320f3 (pager: drop "wait for output to run less" hack). The bug it
> > > worked around was apparently fixed in less back in June 2007.
> > > 
> > > So remove the hack from here as well.
> > > 
> > > Signed-off-by: Arvind Sankar <nivedita@...m.mit.edu>
> > 
> > Looks good to me.
> > 
> >   Acked-by: Josh Poimboeuf <jpoimboe@...hat.com>
> > 
> > Libsubcmd is used by perf and objtool, so adding the perf maintainers to
> > CC.  Arnaldo, do you want to pick this one up?
> 
> Sure, I'll put it in my perf/core branch.
> 
> - Arnaldo
>  
> > > ---
> > >  tools/lib/subcmd/pager.c       | 17 -----------------
> > >  tools/lib/subcmd/run-command.c |  2 --
> > >  tools/lib/subcmd/run-command.h |  1 -
> > >  3 files changed, 20 deletions(-)
> > > 
> > > diff --git a/tools/lib/subcmd/pager.c b/tools/lib/subcmd/pager.c
> > > index 5ba754d17952..94d61d9b511f 100644
> > > --- a/tools/lib/subcmd/pager.c
> > > +++ b/tools/lib/subcmd/pager.c
> > > @@ -1,5 +1,4 @@
> > >  // SPDX-License-Identifier: GPL-2.0
> > > -#include <sys/select.h>
> > >  #include <stdlib.h>
> > >  #include <stdio.h>
> > >  #include <string.h>
> > > @@ -23,21 +22,6 @@ void pager_init(const char *pager_env)
> > >  	subcmd_config.pager_env = pager_env;
> > >  }
> > >  
> > > -static void pager_preexec(void)
> > > -{
> > > -	/*
> > > -	 * Work around bug in "less" by not starting it until we
> > > -	 * have real input
> > > -	 */
> > > -	fd_set in;
> > > -
> > > -	FD_ZERO(&in);
> > > -	FD_SET(0, &in);
> > > -	select(1, &in, NULL, &in, NULL);
> > > -
> > > -	setenv("LESS", "FRSX", 0);
> > > -}
> > > -
> > >  static const char *pager_argv[] = { "sh", "-c", NULL, NULL };
> > >  static struct child_process pager_process;
> > >  
> > > @@ -84,7 +68,6 @@ void setup_pager(void)
> > >  	pager_argv[2] = pager;
> > >  	pager_process.argv = pager_argv;
> > >  	pager_process.in = -1;
> > > -	pager_process.preexec_cb = pager_preexec;
> > >  
> > >  	if (start_command(&pager_process))
> > >  		return;
> > > diff --git a/tools/lib/subcmd/run-command.c b/tools/lib/subcmd/run-command.c
> > > index 5cdac2162532..9e9dca717ed7 100644
> > > --- a/tools/lib/subcmd/run-command.c
> > > +++ b/tools/lib/subcmd/run-command.c
> > > @@ -120,8 +120,6 @@ int start_command(struct child_process *cmd)
> > >  					unsetenv(*cmd->env);
> > >  			}
> > >  		}
> > > -		if (cmd->preexec_cb)
> > > -			cmd->preexec_cb();
> > >  		if (cmd->exec_cmd) {
> > >  			execv_cmd(cmd->argv);
> > >  		} else {
> > > diff --git a/tools/lib/subcmd/run-command.h b/tools/lib/subcmd/run-command.h
> > > index 17d969c6add3..6256268802b5 100644
> > > --- a/tools/lib/subcmd/run-command.h
> > > +++ b/tools/lib/subcmd/run-command.h
> > > @@ -46,7 +46,6 @@ struct child_process {
> > >  	unsigned no_stderr:1;
> > >  	unsigned exec_cmd:1; /* if this is to be external sub-command */
> > >  	unsigned stdout_to_stderr:1;
> > > -	void (*preexec_cb)(void);
> > >  };
> > >  
> > >  int start_command(struct child_process *);
> > > -- 
> > > 2.13.6
> > > 
> > 
> > -- 
> > Josh