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

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Date:	Mon, 06 Oct 2014 14:51:06 +0200
From:	Robert Baldyga <r.baldyga@...sung.com>
To:	Michal Nazarewicz <mina86@...a86.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
Subject: Re: [PATCH] usb: gadget: f_fs: add "zombie" mode

On 10/06/2014 02:36 PM, Michal Nazarewicz wrote:
> 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?

Shouldn't be error-prone, because opening them will fail with -ENODEV,
but indeed it can be confusing. I will try to do something about that :)

> 
>>
>> 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
> 

Thanks,
Robert Baldyga
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