linux-kernel - Re: [PATCH v5] usb: gadget: f_fs: add "no

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Date:	Wed, 24 Dec 2014 15:32:32 +0100
From:	Michal Nazarewicz <mina86@...a86.com>
To:	Robert Baldyga <r.baldyga@...sung.com>, balbi@...com
Cc:	gregkh@...uxfoundation.org, linux-usb@...r.kernel.org,
	linux-kernel@...r.kernel.org, m.szyprowski@...sung.com,
	k.opasiak@...sung.com, stern@...land.harvard.edu,
	Robert Baldyga <r.baldyga@...sung.com>
Subject: Re: [PATCH v5] usb: gadget: f_fs: add "no_disconnect" mode

On Thu, Dec 18 2014, Robert Baldyga wrote:
> Since we can compose gadgets from many functions, there is the problem
> related to gadget breakage while FunctionFS daemon being closed. FFS
> function is userspace code so there is no way to know when it will close
> files (it doesn't matter what is the reason of this situation, it can
> be daemon logic, program breakage, process kill or any other). So when
> we have another function in gadget which, for example, sends some amount
> of data, does some software update or implements some real-time functionality,
> we may want to keep the gadget connected despite FFS function is no longer
> functional.
>
> We can't just remove one of functions from gadget since it has been
> enumerated, so the only way to keep entire gadget working is to make
> broken FFS function deactivated but still visible to host. For this
> purpose this patch introduces "no_disconnect" mode. It can be enabled
> by setting mount option "no_disconnect=1", and results with defering
> function disconnect to the moment of reopen ep0 file or filesystem
> unmount. After closing all endpoint files, FunctionFS is set to state
> FFS_DEACTIVATED.
>
> When ffs->state == FFS_DEACTIVATED:
> - function is still bound and visible to host,
> - setup requests are automatically stalled,
> - transfers on other endpoints are refused,
> - epfiles, except ep0, are deleted from the filesystem,
> - opening ep0 causes the function to be closed, and then FunctionFS
>   is ready for descriptors and string write,
> - altsetting change causes the function to be closed - we want to keep
>   function alive until another functions are potentialy used, altsetting
>   change means that another configuration is being selected or USB cable
>   was unplugged, which indicates that we don't need to stay longer in
>   FFS_DEACTIVATED state
> - unmounting of the FunctionFS instance causes the function to be closed.
>
> Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>

Acked-by: Michal Nazarewicz <mina86@...a86.com>

> @@ -1417,7 +1429,11 @@ static void ffs_data_opened(struct ffs_data *ffs)
>  	ENTER();
>  
>  	atomic_inc(&ffs->ref);
> -	atomic_inc(&ffs->opened);
> +	if (atomic_add_return(1, &ffs->opened) == 1)
> +		if (ffs->state == FFS_DEACTIVATED) {
> +			ffs->state = FFS_CLOSING;
> +			ffs_data_reset(ffs);
> +	}

Wrong indention.  Why not:

+	if (atomic_add_return(1, &ffs->opened) == 1 &&
+	    ffs->state == FFS_DEACTIVATED) {
+		ffs->state = FFS_CLOSING;
+		ffs_data_reset(ffs);
+	}

>  }
>  
>  static void ffs_data_put(struct ffs_data *ffs)
> @@ -1439,6 +1455,21 @@ static void ffs_data_closed(struct ffs_data *ffs)

-- 
Best regards,                                         _     _
.o. | Liege of Serenely Enlightened Majesty of      o' \,=./ `o
..o | Computer Science,  Michał “mina86” Nazarewicz    (o o)
ooo +--<mpn@...gle.com>--<xmpp:mina86@...ber.org>--ooO--(_)--Ooo--
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