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    SubjectRe: [PATCH 0/3] *at syscalls: Intro
    Ulrich Drepper wrote:
    > Here is a series of patches which introduce in total 11 new system calls
    > which take a file descriptor/filename pair instead of a single file name.
    > These functions, openat etc, have been discussed on numerous occasions.
    > They are needed to implement race-free filesystem traversal, they are
    > necessary to implement a virtual per-thread current working directory
    > (think multi-threaded backup software), etc.
    >
    > We have in glibc today implementations of the interfaces which use the
    > /proc/self/fd magic. But this code is rather expensive. Here are some
    > results (similar to what Jim Meyering posted before):
    >
    > The test creates a deep directory hierarchy on a tmpfs filesystem.
    > Then rm -fr is used to remove all directories. Without syscall support
    > I get this:
    >
    > real 0m31.921s
    > user 0m0.688s
    > sys 0m31.234s
    >
    > With syscall support the results are much better:
    >
    > real 0m20.699s
    > user 0m0.536s
    > sys 0m20.149s
    >
    >
    > The implemenation is really small:
    >
    > arch/i386/kernel/syscall_table.S | 11 ++
    > arch/x86_64/ia32/ia32entry.S | 11 ++
    > fs/compat.c | 48 +++++++++--
    > fs/exec.c | 2
    > fs/namei.c | 167 ++++++++++++++++++++++++++++++---------
    > fs/open.c | 60 +++++++++++---
    > fs/stat.c | 54 ++++++++++--
    > include/asm-i386/unistd.h | 13 ++-
    > include/asm-x86_64/ia32_unistd.h | 13 ++-
    > include/asm-x86_64/unistd.h | 24 +++++
    > include/linux/fcntl.h | 7 +
    > include/linux/fs.h | 7 +
    > include/linux/namei.h | 7 -
    > include/linux/time.h | 2
    > 14 files changed, 355 insertions(+), 71 deletions(-)
    >
    > I've split the patch in three parts. The first part is the actual
    > code change. It mostly consists of passing down an additional parameter
    > with a file descriptor and add wrapper functions which pass down the
    > default parameter AT_FDCWD. Three new constants are defined in
    > <linux/fcntl.h> which must correspond to the values already in use
    > in glibc. In a few cases I've modified some code which would not
    > necesarily need changing but the change makes it a bit more efficient
    > in presence of the wrapper functions.
    >
    > The real change needed is the additional else-clause in what is now
    > do_path_lookup. That's it.

    Definitely gets my ACK, for my own motivations: I want to create
    race-free cp(1)/mv(1)/rm(1) utilities for my posixutils project.

    It would be nice to add the additional argument to path_lookup(), rather
    than calling do_path_lookup() everywhere.

    Jeff



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