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SubjectRe: [PATCH] Use __unused0 instead of __unused for user visible struct member names
(+cc: some possible relevant people)
Hi,

Guillem Jover wrote:

> On BSD systems __unused has traditionally been defined to mean the
> equivalent of gcc's __attribute__((__unused__)), some parts of the
> Linux tree use that convention too (e.g. perf). The problem comes when
> defining such macro while trying to build unmodified source code with
> BSD origins on systems with Linux headers.
>
> Rename the user visible struct members from __unused to __unused0 to
> not cause compilation failures due to that macro, which should not be
> a problem as those members are supposed to be private anyway.

Thanks, sounds like a good idea.

It would be nice to document one detail: why do these struct members
have a double-underscore before "unused" in the first place? I
understand that libc has (and hence installed kernel headers have) a
limited namespace to work with and they have to be on guard against
applications doing something crazy like

#define unused 0

but aren't there other identifiers in that namespace that work just as
well?

That's not actually an objection --- I'm just curious. __unused1 like
is already used in e.g. asm-generic/stat.h seems fine to me.

Some examples:

> Signed-off-by: Guillem Jover <guillem@hadrons.org>
> ---
[...]
> diff --git a/arch/alpha/include/asm/stat.h b/arch/alpha/include/asm/stat.h
> index 07ad3e6..5754865 100644
> --- a/arch/alpha/include/asm/stat.h
> +++ b/arch/alpha/include/asm/stat.h
> @@ -42,7 +42,7 @@ struct stat64 {
> unsigned long st_mtime_nsec;
> unsigned long st_ctime;
> unsigned long st_ctime_nsec;
> - long __unused[3];
> + long __unused0[3];
> };

This could be

long st_unused[3];

or

long st_padding[3];

> #endif
> diff --git a/arch/arm/include/asm/ucontext.h b/arch/arm/include/asm/ucontext.h
> index 14749ae..7ea9743 100644
> --- a/arch/arm/include/asm/ucontext.h
> +++ b/arch/arm/include/asm/ucontext.h
> @@ -20,7 +20,7 @@ struct ucontext {
> struct sigcontext uc_mcontext;
> sigset_t uc_sigmask;
> /* Allow for uc_sigmask growth. Glibc uses a 1024-bit sigset_t. */
> - int __unused[32 - (sizeof (sigset_t) / sizeof (int))];
> + int __unused0[32 - (sizeof (sigset_t) / sizeof (int))];
> /* Last for extensibility. Eight byte aligned because some
> coprocessors require eight byte alignment. */
> unsigned long uc_regspace[128] __attribute__((__aligned__(8)));

Likewise, this could be something like

int uc_sigmask_padding[32 - ...];

Remainder left unsnipped for convenience of people cc-ed. If the
general idea looks sensible, what would be the best way to usher it
into mainline? Should it be split up into patches for the various
arch-specific trees, or should acks from relevant people be collected
some other way?

Thanks,
Jonathan

> diff --git a/arch/ia64/include/asm/stat.h b/arch/ia64/include/asm/stat.h
> index 367bb90..2ec0d4c 100644
> --- a/arch/ia64/include/asm/stat.h
> +++ b/arch/ia64/include/asm/stat.h
> @@ -24,7 +24,7 @@ struct stat {
> unsigned long st_ctime_nsec;
> unsigned long st_blksize;
> long st_blocks;
> - unsigned long __unused[3];
> + unsigned long __unused0[3];
> };
>
> #define STAT_HAVE_NSEC 1
> diff --git a/arch/mips/include/asm/compat.h b/arch/mips/include/asm/compat.h
> index b77df03..333d49f 100644
> --- a/arch/mips/include/asm/compat.h
> +++ b/arch/mips/include/asm/compat.h
> @@ -84,7 +84,7 @@ struct compat_flock {
> compat_off_t l_len;
> s32 l_sysid;
> compat_pid_t l_pid;
> - short __unused;
> + short __unused0;
> s32 pad[4];
> };
>
> diff --git a/arch/powerpc/include/asm/ucontext.h b/arch/powerpc/include/asm/ucontext.h
> index d9a4ddf..6121f9e 100644
> --- a/arch/powerpc/include/asm/ucontext.h
> +++ b/arch/powerpc/include/asm/ucontext.h
> @@ -28,7 +28,7 @@ struct ucontext {
> sigset_t uc_sigmask;
> /* glibc has 1024-bit signal masks, ours are 64-bit */
> #ifdef __powerpc64__
> - sigset_t __unused[15]; /* Allow for uc_sigmask growth */
> + sigset_t __unused0[15]; /* Allow for uc_sigmask growth */
> struct sigcontext uc_mcontext; /* last for extensibility */
> #else
> int uc_maskext[30];
> diff --git a/arch/s390/include/asm/stat.h b/arch/s390/include/asm/stat.h
> index d92959e..9577947 100644
> --- a/arch/s390/include/asm/stat.h
> +++ b/arch/s390/include/asm/stat.h
> @@ -95,7 +95,7 @@ struct stat {
> unsigned long st_ctime_nsec;
> unsigned long st_blksize;
> long st_blocks;
> - unsigned long __unused[3];
> + unsigned long __unused0[3];
> };
>
> #endif /* __s390x__ */
> diff --git a/arch/sparc/include/asm/compat.h b/arch/sparc/include/asm/compat.h
> index b8be20d..8f20999 100644
> --- a/arch/sparc/include/asm/compat.h
> +++ b/arch/sparc/include/asm/compat.h
> @@ -107,7 +107,7 @@ struct compat_flock {
> compat_off_t l_start;
> compat_off_t l_len;
> compat_pid_t l_pid;
> - short __unused;
> + short __unused0;
> };
>
> #define F_GETLK64 12
> @@ -120,7 +120,7 @@ struct compat_flock64 {
> compat_loff_t l_start;
> compat_loff_t l_len;
> compat_pid_t l_pid;
> - short __unused;
> + short __unused0;
> };
>
> struct compat_statfs {
> diff --git a/arch/sparc/include/asm/elf_32.h b/arch/sparc/include/asm/elf_32.h
> index 4269ca6..7dffbe2 100644
> --- a/arch/sparc/include/asm/elf_32.h
> +++ b/arch/sparc/include/asm/elf_32.h
> @@ -82,7 +82,7 @@ typedef struct {
> unsigned long pr_regs[32];
> double pr_dregs[16];
> } pr_fr;
> - unsigned long __unused;
> + unsigned long __unused0;
> unsigned long pr_fsr;
> unsigned char pr_qcnt;
> unsigned char pr_q_entrysize;
> diff --git a/arch/sparc/include/asm/elf_64.h b/arch/sparc/include/asm/elf_64.h
> index 7df8b7f..1db74f5 100644
> --- a/arch/sparc/include/asm/elf_64.h
> +++ b/arch/sparc/include/asm/elf_64.h
> @@ -133,7 +133,7 @@ typedef struct {
> unsigned int pr_regs[32];
> unsigned long pr_dregs[16];
> } pr_fr;
> - unsigned int __unused;
> + unsigned int __unused0;
> unsigned int pr_fsr;
> unsigned char pr_qcnt;
> unsigned char pr_q_entrysize;
> diff --git a/arch/sparc/include/asm/fcntl.h b/arch/sparc/include/asm/fcntl.h
> index d0b83f6..a5e8516 100644
> --- a/arch/sparc/include/asm/fcntl.h
> +++ b/arch/sparc/include/asm/fcntl.h
> @@ -47,8 +47,8 @@
> #define F_WRLCK 2
> #define F_UNLCK 3
>
> -#define __ARCH_FLOCK_PAD short __unused;
> -#define __ARCH_FLOCK64_PAD short __unused;
> +#define __ARCH_FLOCK_PAD short __unused0;
> +#define __ARCH_FLOCK64_PAD short __unused0;
>
> #include <asm-generic/fcntl.h>
>
> diff --git a/arch/sparc/include/asm/stat.h b/arch/sparc/include/asm/stat.h
> index a232e9e..7258fb4 100644
> --- a/arch/sparc/include/asm/stat.h
> +++ b/arch/sparc/include/asm/stat.h
> @@ -43,7 +43,7 @@ struct stat64 {
> unsigned long st_mtime_nsec;
> unsigned long st_ctime;
> unsigned long st_ctime_nsec;
> - long __unused[3];
> + long __unused0[3];
> };
>
> #else
> diff --git a/arch/tile/include/asm/compat.h b/arch/tile/include/asm/compat.h
> index bf95f55..6f31f94 100644
> --- a/arch/tile/include/asm/compat.h
> +++ b/arch/tile/include/asm/compat.h
> @@ -80,7 +80,7 @@ struct compat_sysctl {
> unsigned int oldlenp;
> unsigned int newval;
> unsigned int newlen;
> - unsigned int __unused[4];
> + unsigned int __unused0[4];
> };
>
>
> diff --git a/arch/x86/include/asm/stat.h b/arch/x86/include/asm/stat.h
> index e0b1d9b..a7fb9e5 100644
> --- a/arch/x86/include/asm/stat.h
> +++ b/arch/x86/include/asm/stat.h
> @@ -85,7 +85,7 @@ struct stat {
> unsigned long st_mtime_nsec;
> unsigned long st_ctime;
> unsigned long st_ctime_nsec;
> - long __unused[3];
> + long __unused0[3];
> };
> #endif
>
> diff --git a/include/linux/icmp.h b/include/linux/icmp.h
> index 474f2a5..124e861 100644
> --- a/include/linux/icmp.h
> +++ b/include/linux/icmp.h
> @@ -76,7 +76,7 @@ struct icmphdr {
> } echo;
> __be32 gateway;
> struct {
> - __be16 __unused;
> + __be16 __unused0;
> __be16 mtu;
> } frag;
> } un;
> diff --git a/include/linux/sysctl.h b/include/linux/sysctl.h
> index 703cfa3..9911ac5 100644
> --- a/include/linux/sysctl.h
> +++ b/include/linux/sysctl.h
> @@ -40,7 +40,7 @@ struct __sysctl_args {
> size_t __user *oldlenp;
> void __user *newval;
> size_t newlen;
> - unsigned long __unused[4];
> + unsigned long __unused0[4];
> };
>
> /* Define sysctl names first */
> --
> 1.7.7.3
>
>


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