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

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Message-ID: <20150113163216.GH16533@saruman>
Date:	Tue, 13 Jan 2015 10:32:16 -0600
From:	Felipe Balbi <balbi@...com>
To:	Robert Baldyga <r.baldyga@...sung.com>
CC:	<balbi@...com>, <gregkh@...uxfoundation.org>,
	<linux-usb@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<mina86@...a86.com>, <m.szyprowski@...sung.com>,
	<k.opasiak@...sung.com>, <stern@...land.harvard.edu>
Subject: Re: [PATCH v5] usb: gadget: f_fs: add "no_disconnect" mode

Hi,

On Thu, Dec 18, 2014 at 09:55:10AM +0100, 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>
> 
> Changelog:
> 
> v5:
> - close function on altsetting change
> 
> v4: https://lkml.org/lkml/2014/10/9/224
> - use ffs_data_reset() instead of ffs_data_clear() to reset ffs data
>   properly after ffs->ref refcount reach 0 (or under in no_disconnect
>   mode) in ffs_data_put() function
> 
> v3: https://lkml.org/lkml/2014/10/9/170
> - change option name to more descriptive and less scary,
> - fix cleaning up on unmount (call ffs_data_closed() in ffs_fs_kill_sb(),
>   and ffs_data_clear() in ffs_data_closed() if ffs->opened is negative).
> 
> v2: https://lkml.org/lkml/2014/10/7/109
> - delete epfiles, excepting ep0, when FFS is in "zombie" mode,
> - add description of FFS_ZOMBIE state,
> - minor cleanups.
> 
> v1: https://lkml.org/lkml/2014/10/6/128

This changelog should be after the tearline, I've manually editted it
and also applied the small modification sugested by Michal. It should
show up on my testing/next soonish.

-- 
balbi

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