From: Krzysztof Opasiak <k.opasiak@samsung.com>
To: "'Michal Nazarewicz'" <mina86@mina86.com>, "'Felipe Balbi'" <balbi@ti.com>
Cc: Krzysztof Opasiak <k.opasiak@samsung.com>, linux-usb@vger.kernel.org,
        linux-kernel@vger.kernel.org
References: <1401954206-8491-1-git-send-email-mina86@mina86.com>
 <1401954206-8491-2-git-send-email-mina86@mina86.com>
In-reply-to: <1401954206-8491-2-git-send-email-mina86@mina86.com>
Subject: RE: [PATCH 2/2] tools: ffs-test: convert to new descriptor format
 fixing compilation error
Date: Thu, 05 Jun 2014 13:25:01 +0200
Message-id: <008101cf80b0$caf88dc0$60e9a940$%opasiak@samsung.com>
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Sender: linux-kernel-owner@vger.kernel.org

Hi,

> -----Original Message-----
> From: Michal Nazarewicz [mailto:mina86@mina86.com]
> Sent: Thursday, June 05, 2014 9:43 AM
> To: Felipe Balbi
> Cc: Krzysztof Opasiak; linux-usb@vger.kernel.org; linux-
> kernel@vger.kernel.org; Michal Nazarewicz
> Subject: [PATCH 2/2] tools: ffs-test: convert to new descriptor
> format fixing compilation error
> 
> Commit [ac8dde11: “usb: gadget: f_fs: Add flags to descriptors
> block”]
> which introduced a new descriptor format for FunctionFS removed the
> usb_functionfs_descs_head structure, which is still used by ffs-
> test.
> tool.
> 
> Convert ffs-test by converting it to use the new header format.
> For
> testing kernels prior to 3.14 (when the new format was introduced)
> and
> parsing of the legacy headers in the new kernels, provide a
> compilation
> flag to make the tool use the old format.
> 
> Finally, include information as to when the legacy FunctionFS
> headers
> format has been deprecated (which is also when the new one has been
> introduced).
> 
> Reported-by: Lad, Prabhakar <prabhakar.csengg@gmail.com>
> Reported-by: Krzysztof Opasiak <k.opasiak@samsung.com>
> Signed-off-by: Michal Nazarewicz <mina86@mina86.com>

(...)

> 
>  static const struct {
> -	struct usb_functionfs_descs_head header;
> +	struct {
> +		__le32 magic;
> +		__le32 length;
> +#ifndef USE_LEGACY_DESC_HEAD
> +		__le32 flags;
> +#endif
> +		__le32 fs_count;
> +		__le32 hs_count;
> +	} __attribute__((packed)) header;

I would suggest adding a suitable structure as you described in previous discussion[1]. Writing first 3 fields in each userspace program doesn't look quite good. Using:

#ifndef USE_LEGACY_DESC_HEAD
struct {
	struct usb_functionfs_desc_head2 header;
	__le32 fs_count
	(... and rest according to flags ...)
} __attribute__((packed)) header;
#else ...

Would be shorter, more flexible and user friendly. Moreover it gives less places for mistake (writing fields in wrong order).

Footnotes:
1 - http://marc.info/?l=linux-usb&m=140190878901586&w=2


--
BR's
Krzysztof Opasiak
Samsung R&D Institute Poland
Samsung Electronics
k.opasiak@samsung.com


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