linux-kernel - RE: [Resend PATCH v2] testusb: add path /dev/bus/usb to default search paths of usbfs

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Date:	Tue, 22 May 2012 03:41:54 +0000
From:	"Du, ChangbinX" <changbinx.du@...el.com>
To:	David Rientjes <rientjes@...gle.com>
CC:	"gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
	Sergei Shtylyov <sshtylyov@...sta.com>,
	"mina86@...a86.com" <mina86@...a86.com>,
	"Fleming, Matt" <matt.fleming@...el.com>,
	"balbi@...com" <balbi@...com>, "hpa@...or.com" <hpa@...or.com>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-usb@...r.kernel.org" <linux-usb@...r.kernel.org>
Subject: RE: [Resend PATCH v2] testusb: add path /dev/bus/usb to default
 search paths of usbfs

On Tue, 22 May 2012, Du, ChangbinX wrote:

> As real device-nodes managed by udev whose nodes lived in /dev/bus/usb are mostly used today, let testusb tool use that directory as one default path make tool be more convenient to use.
> 
> Signed-off-by: Du Changbin <changbinx.du@...el.com>
> ---
>  tools/usb/testusb.c |    5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/tools/usb/testusb.c b/tools/usb/testusb.c index 
> 6e0f567..82d7c59 100644
> --- a/tools/usb/testusb.c
> +++ b/tools/usb/testusb.c
> @@ -358,6 +358,7 @@ static const char *usbfs_dir_find(void)  {
>  	static char usbfs_path_0[] = "/dev/usb/devices";
>  	static char usbfs_path_1[] = "/proc/bus/usb/devices";
> +	static char udev_usb_path[] = "/dev/bus/usb";
>  
>  	static char *const usbfs_paths[] = {
>  		usbfs_path_0, usbfs_path_1
> @@ -376,6 +377,10 @@ static const char *usbfs_dir_find(void)
>  		}
>  	} while (++it != end);
>  
> +	/* real device-nodes managed by udev */
> +	if (access(udev_usb_path, F_OK) == 0)
> +		return udev_usb_path;
> +
>  	return NULL;
>  }
>  

Two issues with this: F_OK only guarantees that the path exists, it does not guarantee that it is readable like this function guarantees for usbfs_paths, and access() shouldn't be used because of its security implications, you're better off using open() and testing for fd.

Hello, David. I think this function doesn't need check the permission. What this function need do is to find the usbfs mount point. If the path exists but cannot read, we cannot report as it's not exits. And when we read files, open() will return an error and user can check if it's need to upgrade his access right.
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