linux-kernel - Re: [PATCH v2 1/6] mtd: spi-nor: change return value of read/write

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Date:	Wed, 5 Aug 2015 10:27:05 +0200
From:	Michal Suchanek <hramrach@...il.com>
To:	Marek Vasut <marex@...x.de>
Cc:	David Woodhouse <dwmw2@...radead.org>,
	Brian Norris <computersforpeace@...il.com>,
	Han Xu <han.xu@...escale.com>,
	Rafał Miłecki <zajec5@...il.com>,
	Huang Shijie <b32955@...escale.com>,
	Ben Hutchings <ben@...adent.org.uk>,
	Gabor Juhos <juhosg@...nwrt.org>,
	Bean Huo 霍斌斌 <beanhuo@...ron.com>,
	MTD Maling List <linux-mtd@...ts.infradead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Hou Zhiqiang <B48286@...escale.com>,
	Huang Shijie <shijie.huang@...el.com>
Subject: Re: [PATCH v2 1/6] mtd: spi-nor: change return value of read/write

On 4 August 2015 at 18:42, Marek Vasut <marex@...x.de> wrote:
> On Tuesday, August 04, 2015 at 08:42:51 AM, Michal Suchanek wrote:
>> On 3 August 2015 at 23:46, Marek Vasut <marex@...x.de> wrote:
>> > On Monday, August 03, 2015 at 08:39:01 PM, Michal Suchanek wrote:
>> >> Change the return value of spi-nor device read and write methods to
>> >> allow returning amount of data transferred and errors as
>> >> read(2)/write(2) does.
>> >>
>> >> Signed-off-by: Michal Suchanek <hramrach@...il.com>
>> >> ---
>> >>
>> >>  include/linux/mtd/spi-nor.h | 4 ++--
>> >>  1 file changed, 2 insertions(+), 2 deletions(-)
>> >>
>> >> diff --git a/include/linux/mtd/spi-nor.h b/include/linux/mtd/spi-nor.h
>> >> index e540952..7d782cb 100644
>> >> --- a/include/linux/mtd/spi-nor.h
>> >> +++ b/include/linux/mtd/spi-nor.h
>> >> @@ -185,9 +185,9 @@ struct spi_nor {
>> >>
>> >>       int (*write_reg)(struct spi_nor *nor, u8 opcode, u8 *buf, int len,
>> >>
>> >>                       int write_enable);
>> >>
>> >> -     int (*read)(struct spi_nor *nor, loff_t from,
>> >> +     ssize_t (*read)(struct spi_nor *nor, loff_t from,
>> >>
>> >>                       size_t len, size_t *retlen, u_char *read_buf);
>> >>
>> >> -     void (*write)(struct spi_nor *nor, loff_t to,
>> >> +     ssize_t (*write)(struct spi_nor *nor, loff_t to,
>> >>
>> >>                       size_t len, size_t *retlen, const u_char
>> >>                       *write_buf);
>> >>
>> >>       int (*erase)(struct spi_nor *nor, loff_t offs);
>> >
>> > You realize that if someone does bisect and has only this patch applied,
>> > the compiler will complain loudly about mismatching data types, right ?
>> > :)
>>
>> Yes, the compiler prints a warning. However, only the return value
>> which is not used changes so it should not cause any real problem.
>
> Are you certain that ssize_t is equal to int , always , everywhere ? :-)

No, it's larger or equal.

> Note that it is possible to do such conversion even without introducing
> compiler warnings along the way -- just do the data type conversion first
> and the other changes in subsequent patches. It will be clear that one
> patch does one thing then.

If this is the only concern with these patches it is easily amended ;-)

Thanks

Michal
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