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Date: Wed, 10 Oct 2018 21:43:39 +0200 From: Miguel Ojeda <miguel.ojeda.sandonis@...il.com> To: "Ted Ts'o" <tytso@....edu>, Arnd Bergmann <arnd@...db.de>, Andreas Dilger <adilger.kernel@...ger.ca>, jack@...e.cz, Eric Biggers <ebiggers@...gle.com>, Ext4 Developers List <linux-ext4@...r.kernel.org>, linux-kernel <linux-kernel@...r.kernel.org> Subject: Re: [PATCH] ext4: avoid unused variable warning Hi Ted, On Wed, Oct 10, 2018 at 9:27 PM Theodore Y. Ts'o <tytso@....edu> wrote: > > On Wed, Oct 10, 2018 at 04:27:58PM +0200, Arnd Bergmann wrote: > > The two new variables are only used in an #ifdef, so they cause a > > warning without CONFIG_QUOTA: > > > > fs/ext4/super.c: In function 'parse_options': > > fs/ext4/super.c:1977:26: error: unused variable 'grp_qf_name' [-Werror=unused-variable] > > char *p, *usr_qf_name, *grp_qf_name; > > ^~~~~~~~~~~ > > fs/ext4/super.c:1977:12: error: unused variable 'usr_qf_name' [-Werror=unused-variable] > > char *p, *usr_qf_name, *grp_qf_name; > > > > Fixes: 20cefcdc2040 ("ext4: fix use-after-free race in ext4_remount()'s error path") > > Signed-off-by: Arnd Bergmann <arnd@...db.de> > > Hmm, I wonder if we should do something like: > > #define EXT4_UNUSED_VAR __attribute__ ((unused)) We have __maybe_unused already, so you can go ahead! :-) (Also __always_unused, same definition as well, but here it does not may sense). > > and then we could do: > > char *p, *usr_qf_name EXT4_UNUSED_VAR, *grp_qf_name EXT4_UNUSED_VAR; > > More generally, I wonder if this is something we should have defined > for the whole kernel, as opposed to a one-off hack that ACPI and ext4 > subsystems use. It's a little ugly, but I think it's much nicer than > having extra #ifdefs such as: > > char *p; > #ifdef CONFIG_QUOTA > char *usr_qf_name, *grp_qf_name; > #endif > > After all, the compiler is perfectly capable of ignoring variables > which are unused. And if it's only because of an #ifdef later in the > function, it would be nice to not have an extra #ifdef in the variable > declarations. Indeed, it looks clean --- I like it. Although I am not sure how people will feel about that :-) Someone may argue that, for consistency, we shouldn't, because inside structs we have to use #ifdefs still. Cheers, Miguel
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