linux-kernel - Re: [PATCH 1/8] NTB: ntb_tool: reading the link file should not end in a NULL byte

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Message-ID: <20180615194748.GA15481@mobilestation>
Date:   Fri, 15 Jun 2018 22:47:48 +0300
From:   Serge Semin <fancer.lancer@...il.com>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-ntb@...glegroups.com,
        Jon Mason <jdmason@...zu.us>,
        Dave Jiang <dave.jiang@...el.com>,
        Allen Hubbe <allenbh@...il.com>,
        Shyam Sundar S K <Shyam-sundar.S-k@....com>,
        Shuah Khan <shuah@...nel.org>
Subject: Re: [PATCH 1/8] NTB: ntb_tool: reading the link file should not end
 in a NULL byte

On Fri, Jun 08, 2018 at 06:08:11PM -0600, Logan Gunthorpe <logang@...tatee.com> wrote:
> When running ntb_test this warning is issued:
> 
> ./ntb_test.sh: line 200: warning: command substitution: ignored null
> byte in input
> 

This is weird. Neither me nor the folks' who tested the script saw this warning.
I tried it on my laptop with bash and on a target device with busybox-shell. The
warning never occurred. I even tried a simple command like:
[[ $(echo -ne "\x4e\x0a\00") == "N" ]] && echo "True"

It might be that your bash is more modern than mine. Anyway if this patch solves the
problem you see, that's great. Thanks for it.

-Sergey

> This is caused by the kernel returning one more byte than is necessary
> when reading the link file.
> 
> Reduce the number of bytes read back to 2 as it was before the
> commit that regressed this.
> 
> Fixes: 7f46c8b3a552 ("NTB: ntb_tool: Add full multi-port NTB API support")
> Signed-off-by: Logan Gunthorpe <logang@...tatee.com>
> ---
>  drivers/ntb/test/ntb_tool.c | 3 +--
>  1 file changed, 1 insertion(+), 2 deletions(-)
> 
> diff --git a/drivers/ntb/test/ntb_tool.c b/drivers/ntb/test/ntb_tool.c
> index d592c0ffbd19..ec5cf095cdb9 100644
> --- a/drivers/ntb/test/ntb_tool.c
> +++ b/drivers/ntb/test/ntb_tool.c
> @@ -504,7 +504,7 @@ static ssize_t tool_peer_link_read(struct file *filep, char __user *ubuf,
>  	buf[1] = '\n';
>  	buf[2] = '\0';
>  
> -	return simple_read_from_buffer(ubuf, size, offp, buf, 3);
> +	return simple_read_from_buffer(ubuf, size, offp, buf, 2);
>  }
>  
>  static TOOL_FOPS_RDWR(tool_peer_link_fops,
> @@ -1690,4 +1690,3 @@ static void __exit tool_exit(void)
>  	debugfs_remove_recursive(tool_dbgfs_topdir);
>  }
>  module_exit(tool_exit);
> -
> -- 
> 2.11.0
>