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    Subject[PATCH 0/3] *at syscalls: Intro
    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.

    The other two patches contain the syscall definitions for x86 and x86-64.
    I've tested the code on x86-64, including the ia32 compat code. Because
    there is no architecture specific change all should work well on other
    archs once the syscalls are added.
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      Last update: 2005-12-15 23:52    [W:0.020 / U:40.620 seconds]
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