Messages in this thread | | | Date | Thu, 15 Dec 2005 17:49:33 -0500 | From | Ulrich Drepper <> | Subject | [PATCH 0/3] *at syscalls: Intro |
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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. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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