• Gerd Hoffmann's avatar
    preadv/pwritev: Add preadv and pwritev system calls. · f3554f4b
    Gerd Hoffmann authored
    This patch adds preadv and pwritev system calls.  These syscalls are a
    pretty straightforward combination of pread and readv (same for write).
    They are quite useful for doing vectored I/O in threaded applications.
    Using lseek+readv instead opens race windows you'll have to plug with
    locking.
    
    Other systems have such system calls too, for example NetBSD, check
    here: http://www.daemon-systems.org/man/preadv.2.html
    
    The application-visible interface provided by glibc should look like
    this to be compatible to the existing implementations in the *BSD family:
    
      ssize_t preadv(int d, const struct iovec *iov, int iovcnt, off_t offset);
      ssize_t pwritev(int d, const struct iovec *iov, int iovcnt, off_t offset);
    
    This prototype has one problem though: On 32bit archs is the (64bit)
    offset argument unaligned, which the syscall ABI of several archs doesn't
    allow to do.  At least s390 needs a wrapper in glibc to handle this.  As
    we'll need a wrappers in glibc anyway I've decided to push problem to
    glibc entriely and use a syscall prototype which works without
    arch-specific wrappers inside the kernel: The offset argument is
    explicitly splitted into two 32bit values.
    
    The patch sports the actual system call implementation and the windup in
    the x86 system call tables.  Other archs follow as separate patches.
    Signed-off-by: default avatarGerd Hoffmann <kraxel@redhat.com>
    Cc: Arnd Bergmann <arnd@arndb.de>
    Cc: Al Viro <viro@zeniv.linux.org.uk>
    Cc: <linux-api@vger.kernel.org>
    Cc: <linux-arch@vger.kernel.org>
    Cc: Ralf Baechle <ralf@linux-mips.org>
    Cc: Ingo Molnar <mingo@elte.hu>
    Cc: Thomas Gleixner <tglx@linutronix.de>
    Cc: "H. Peter Anvin" <hpa@zytor.com>
    Signed-off-by: default avatarAndrew Morton <akpm@linux-foundation.org>
    Signed-off-by: default avatarLinus Torvalds <torvalds@linux-foundation.org>
    f3554f4b
compat.h 9.3 KB