Re: [PATCH v2 properly indented] fix start_command() bug when stdin is closed

[Junio C Hamano <gitster@xxxxxxxxx>]

Paolo Bonzini <bonzini@xxxxxxx> writes:

>  int start_command(struct child_process *cmd)
>  {
>  	int need_in, need_out, need_err;
>  	int fdin[2], fdout[2], fderr[2];
>  
>  	/*
> +	 * Make sure that all file descriptors <= 2 are open, otherwise we
> +	 * mess them up when dup'ing pipes onto stdin/stdout/stderr.  Since
> +	 * we are at it, save a file descriptor on /dev/null to use it later.
> +	 */
> +	if (devnull_fd == -1) {
> +		devnull_fd = open("/dev/null", O_RDWR);
> +		while (devnull_fd >= 0 && devnull_fd <= 2)
> +			devnull_fd = dup(devnull_fd);
> +		if (devnull_fd == -1)
> +			die("opening /dev/null failed (%s)", strerror(errno));
> +	}
> +

I may be misreading the patch but, this logic always opens /dev/null, if
nobody asked for *any* cmd->no_stdXXX and low 3 fds are occupied, and
worse, it keeps fd=3 open.

Making sure low fds 0, 1 and 2 are open is a good thing.  I do not think
clobbering fd=3 is good.

Also shouldn't this be done only on the side that dup()s fds around,
i.e. in the child process after fork()?  Why is this done for the parent?



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