linux-kernel - Re: [PATCH] usb: gadget: f

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Date:	Mon, 06 Oct 2014 14:36:15 +0200
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, andrzej.p@...sung.com,
	k.opasiak@...sung.com, Robert Baldyga <r.baldyga@...sung.com>
Subject: Re: [PATCH] usb: gadget: f_fs: add "zombie" mode

On Mon, Oct 06 2014, Robert Baldyga <r.baldyga@...sung.com> wrote:
> Since we can compose gadgets from many functions, there is the problem
> related to gadget breakage while FunctionFS daemon being closed. In some
> cases it's strongly desired to keep gadget alive for a while, despite
> FunctionFS files are closed, to allow another functions to complete
> some presumably critical operations.
>
> For this purpose this patch introduces "zombie" mode. It can be enabled
> by setting mount option "zombie=1", and results with defering function
> closure to the moment of reopening ep0 file or filesystem umount.
>
> When ffs->state == FFS_ZOMBIE:
> - function is still binded and visible to host,
> - setup requests are automatically stalled,
> - all another transfers are refused,
> - opening ep0 causes function close, and then FunctionFS is ready for
>   descriptors and string write,
> - umount of functionfs cause function close.

However, all the ep# files will still exist on the filesystem.  This may
be a bit confusing and error-prone, no?

>
> Signed-off-by: Robert Baldyga <r.baldyga@...sung.com>
> ---
>  drivers/usb/gadget/function/f_fs.c | 25 ++++++++++++++++++++++---
>  drivers/usb/gadget/function/u_fs.h |  4 ++++
>  2 files changed, 26 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/usb/gadget/function/f_fs.c b/drivers/usb/gadget/function/f_fs.c
> @@ -1222,6 +1225,12 @@ static int ffs_fs_parse_opts(struct ffs_sb_fill_data *data, char *opts)
>  
>  		/* Interpret option */
>  		switch (eq - opts) {
> +		case 6:
> +			if (!memcmp(opts, "zombie", 6))
> +				data->zombie_mode  = !!value;

Unnecessary double space before =.

> +			else
> +				goto invalid;
> +			break;
>  		case 5:
>  			if (!memcmp(opts, "rmode", 5))
>  				data->root_mode  = (value & 0555) | S_IFDIR;
> diff --git a/drivers/usb/gadget/function/u_fs.h b/drivers/usb/gadget/function/u_fs.h
> @@ -92,6 +92,8 @@ enum ffs_state {
>  	 */
>  	FFS_ACTIVE,
>  
> +	FFS_ZOMBIE,
> +

Add comment describing the state.

>  	/*
>  	 * All endpoints have been closed.  This state is also set if
>  	 * we encounter an unrecoverable error.  The only

-- 
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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