Re: Remove __ASSUME_COMPLETE_READV_WRITEV

[Will Newton <will dot newton at linaro dot org>]

On 20 June 2014 17:00, Joseph S. Myers <joseph@codesourcery.com> wrote:
> This patch removes the __ASSUME_COMPLETE_READV_WRITEV
> kernel-features.h macro, now that it can be unconditionally assumed to
> be true.  (The relevant kernel feature was added some time between 2.0
> and 2.2, and this macro is only used in sysdeps/unix/sysv/linux/.)
>
> Tested x86_64 that the disassembly of installed shared libraries is
> unchanged by this patch.
>
> 2014-06-20  Joseph Myers  <joseph@codesourcery.com>
>
>         * sysdeps/unix/sysv/linux/kernel-features.h
>         (__ASSUME_COMPLETE_READV_WRITEV): Remove macro.
>         * sysdeps/unix/sysv/linux/readv.c: Do not include
>         <kernel-features.h>.
>         [!__ASSUME_COMPLETE_READV_WRITEV]: Remove conditional code.
>         [!UIO_FASTIOV] (UIO_FASTIOV): Remove macro.
>         (__libc_readv) [__ASSUME_COMPLETE_READV_WRITEV]: Make code
>         unconditional.
>         (__libc_readv) [!__ASSUME_COMPLETE_READV_WRITEV]: Remove
>         conditional code.
>         * sysdeps/unix/sysv/linux/writev.c: Do not include
>         <kernel-features.h>.
>         [!__ASSUME_COMPLETE_READV_WRITEV]: Remove conditional code.
>         [!UIO_FASTIOV] (UIO_FASTIOV): Remove macro.
>         (__libc_writev) [__ASSUME_COMPLETE_READV_WRITEV]: Make code
>         unconditional.
>         (__libc_writev) [!__ASSUME_COMPLETE_READV_WRITEV]: Remove
>         conditional code.

This looks ok to me.

> diff --git a/sysdeps/unix/sysv/linux/kernel-features.h b/sysdeps/unix/sysv/linux/kernel-features.h
> index 026f89f..acc7ca3 100644
> --- a/sysdeps/unix/sysv/linux/kernel-features.h
> +++ b/sysdeps/unix/sysv/linux/kernel-features.h
> @@ -94,11 +94,6 @@
>  # define __ASSUME_SET_ROBUST_LIST      1
>  #endif
>
> -/* Pessimistically assume that 2.6.18 introduced real handling of
> -   large numbers of requests to readv and writev and that we don't
> -   need a fallback.  It likely worked for much longer.  */
> -#define __ASSUME_COMPLETE_READV_WRITEV 1
> -
>  /* Support for PI futexes was added in 2.6.18 (but some architectures
>     lack futex_atomic_cmpxchg_inatomic in some configurations).  */
>  #if !(defined __sparc__ && !defined __arch64__ && !defined __sparc_v9__)
> diff --git a/sysdeps/unix/sysv/linux/readv.c b/sysdeps/unix/sysv/linux/readv.c
> index 48eae46..a977d17 100644
> --- a/sysdeps/unix/sysv/linux/readv.c
> +++ b/sysdeps/unix/sysv/linux/readv.c
> @@ -23,19 +23,8 @@
>
>  #include <sysdep-cancel.h>
>  #include <sys/syscall.h>
> -#include <kernel-features.h>
> -
> -#ifndef __ASSUME_COMPLETE_READV_WRITEV
> -static ssize_t __atomic_readv_replacement (int, const struct iovec *,
> -                                          int) internal_function;
> -#endif
> -
> -
> -/* Not all versions of the kernel support the large number of records.  */
> -#ifndef UIO_FASTIOV
> -# define UIO_FASTIOV   8       /* 8 is a safe number.  */
> -#endif
>
> +/* Consider moving to syscalls.list.  */
>
>  ssize_t
>  __libc_readv (fd, vector, count)
> @@ -56,19 +45,7 @@ __libc_readv (fd, vector, count)
>        LIBC_CANCEL_RESET (oldtype);
>      }
>
> -#ifdef __ASSUME_COMPLETE_READV_WRITEV
>    return result;
> -#else
> -  if (result >= 0 || errno != EINVAL || count <= UIO_FASTIOV)
> -    return result;
> -
> -  return __atomic_readv_replacement (fd, vector, count);
> -#endif
>  }
>  strong_alias (__libc_readv, __readv)
>  weak_alias (__libc_readv, readv)
> -
> -#ifndef __ASSUME_COMPLETE_READV_WRITEV
> -# define __libc_readv static internal_function __atomic_readv_replacement
> -# include <sysdeps/posix/readv.c>
> -#endif
> diff --git a/sysdeps/unix/sysv/linux/writev.c b/sysdeps/unix/sysv/linux/writev.c
> index 06c4c9c..f19221f 100644
> --- a/sysdeps/unix/sysv/linux/writev.c
> +++ b/sysdeps/unix/sysv/linux/writev.c
> @@ -23,19 +23,9 @@
>
>  #include <sysdep-cancel.h>
>  #include <sys/syscall.h>
> -#include <kernel-features.h>
>
> -#ifndef __ASSUME_COMPLETE_READV_WRITEV
> -static ssize_t __atomic_writev_replacement (int, const struct iovec *,
> -                                           int) internal_function;
> -#endif
> -
> -
> -/* Not all versions of the kernel support the large number of records.  */
> -#ifndef UIO_FASTIOV
> -# define UIO_FASTIOV   8       /* 8 is a safe number.  */
> -#endif
>
> +/* Consider moving to syscalls.list.  */
>
>  ssize_t
>  __libc_writev (fd, vector, count)
> @@ -56,19 +46,7 @@ __libc_writev (fd, vector, count)
>        LIBC_CANCEL_RESET (oldtype);
>      }
>
> -#ifdef __ASSUME_COMPLETE_READV_WRITEV
>    return result;
> -#else
> -  if (result >= 0 || errno != EINVAL || count <= UIO_FASTIOV)
> -    return result;
> -
> -  return __atomic_writev_replacement (fd, vector, count);
> -#endif
>  }
>  strong_alias (__libc_writev, __writev)
>  weak_alias (__libc_writev, writev)
> -
> -#ifndef __ASSUME_COMPLETE_READV_WRITEV
> -# define __libc_writev static internal_function __atomic_writev_replacement
> -# include <sysdeps/posix/writev.c>
> -#endif
>
> --
> Joseph S. Myers
> joseph@codesourcery.com



-- 
Will Newton
Toolchain Working Group, Linaro