linux-kernel - Re: [PATCH] mmc: add ifdef around fault_create_debugfs

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Date:	Tue, 10 Nov 2015 18:29:20 +0100
From:	Ulf Hansson <ulf.hansson@...aro.org>
To:	Adrien Schildknecht <adrien+dev@...ischi.me>
Cc:	Shawn Lin <shawn.lin@...k-chips.com>,
	Linus Walleij <linus.walleij@...aro.org>,
	linux-mmc <linux-mmc@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] mmc: add ifdef around fault_create_debugfs_attr()

On 10 November 2015 at 16:04, Adrien Schildknecht
<adrien+dev@...ischi.me> wrote:
> On Mon, 9 Nov 2015 14:33:11 +0100
> Ulf Hansson <ulf.hansson@...aro.org> wrote:
>> On 6 November 2015 at 13:15, Adrien Schildknecht
>> <adrien+dev@...ischi.me> wrote:
>> > FAIL_MMC_REQUEST can be used without FAULT_INJECTION_DEBUG_FS.
>> > In this case fault_create_debugfs_attr() will always return an
>> > error and lead to the deletion of the whole debugfs directory.
>> >
>> > This patch makes sure that FAULT_INJECTION_DEBUG_FS is enabled
>> > before attempting to create the debugfs atttribute.
>> >
>> > Signed-off-by: Adrien Schildknecht <adrien+dev@...ischi.me>
>> > ---
>> >  drivers/mmc/core/debugfs.c | 2 ++
>> >  1 file changed, 2 insertions(+)
>> >
>> > diff --git a/drivers/mmc/core/debugfs.c b/drivers/mmc/core/debugfs.c
>> > index 154aced..13e842c 100644
>> > --- a/drivers/mmc/core/debugfs.c
>> > +++ b/drivers/mmc/core/debugfs.c
>> > @@ -259,11 +259,13 @@ void mmc_add_host_debugfs(struct mmc_host
>> > *host) if (fail_request)
>> >                 setup_fault_attr(&fail_default_attr, fail_request);
>> >         host->fail_mmc_request = fail_default_attr;
>> > +#ifdef CONFIG_FAULT_INJECTION_DEBUG_FS
>> >         if (IS_ERR(fault_create_debugfs_attr("fail_mmc_request",
>> >                                              root,
>> >                                              &host->fail_mmc_request)))
>> >                 goto err_node;
>> >  #endif
>> > +#endif
>> >         return;
>> >
>> >  err_node:
>> > --
>> > 2.6.2
>> >
>>
>> I think you are solving this in the wrong way. Will it really makes
>> sense to use FAIL_MMC_REQUEST unless FAULT_INJECTION_DEBUG_FS is set,
>> I don't think so.
> The fault attribute can be configured using either the debugfs or the
> module parameter "fail_request". It is thus possible to use
> FAIL_MMC_REQUEST without FAULT_INJECTION_DEBUG_FS (even if it is less
> convenient).
>
>> I suggest you to change FAIL_MMC_REQUEST from depending on
>> FAULT_INJECTION to FAULT_INJECTION_DEBUG_FS in /lib/Kconfig.debug.
> The other systems that use the fault injection infrastructure (futex,
> alloc_pages, slab...) can be used without the dependency on
> FAULT_INJECTION_DEBUG_FS. They also use nested #ifdef to handle this

There are also those that chosen to depend on
FAULT_INJECTION_DEBUG_FS, such as FAULT_INJECTION_STACKTRACE_FILTER.

> configuration. I chose the #ifdef approach for the sake of coherence.

I would like to keep the amount of #ifdefs around in the code to a
minimal. In this case it doesn't even make sense and as there are no
consistent behaviour to consider, could you please adopt the Kconfig
solution instead!?

Kind regards
Uffe
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