[PATCH] vfs: *at functions: core

Here is a series of patches which introduce in total 13 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 interfaces are for obvious reasons currently not much used.  But they'll
be used.  coreutils (and Jeff's posixutils) are already using them.
Furthermore, code like ftw/fts in libc (maybe even glob) will also start using
them.  I expect a patch to make follow soon.  Every program which is walking
the filesystem tree will benefit.

Signed-off-by: Ulrich Drepper <drepper@redhat.com>
Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Al Viro <viro@ftp.linux.org.uk>
Acked-by: Ingo Molnar <mingo@elte.hu>
Cc: Michael Kerrisk <mtk-manpages@gmx.net>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

2 files changed, 3 insertions, 3 deletions

diff --git a/arch/alpha/kernel/osf_sys.c b/arch/alpha/kernel/osf_sys.c
index 01fe990d..7fb14f4 100644
--- a/arch/alpha/kernel/osf_sys.c
+++ b/arch/alpha/kernel/osf_sys.c
@@ -960,7 +960,7 @@ osf_utimes(char __user *filename, struct timeval32 __user *tvs)
 			return -EFAULT;
 	}
 
-	return do_utimes(filename, tvs ? ktvs : NULL);
+	return do_utimes(AT_FDCWD, filename, tvs ? ktvs : NULL);
 }
 
 #define MAX_SELECT_SECONDS \
diff --git a/arch/sparc64/kernel/sys_sparc32.c b/arch/sparc64/kernel/sys_sparc32.c
index d4b7a10..9264ccb 100644
--- a/arch/sparc64/kernel/sys_sparc32.c
+++ b/arch/sparc64/kernel/sys_sparc32.c
@@ -821,7 +821,7 @@ asmlinkage long sys32_utimes(char __user *filename,
 			return -EFAULT;
 	}
 
-	return do_utimes(filename, (tvs ? &ktvs[0] : NULL));
+	return do_utimes(AT_FDCWD, filename, (tvs ? &ktvs[0] : NULL));
 }
 
 /* These are here just in case some old sparc32 binary calls it. */
@@ -1003,7 +1003,7 @@ asmlinkage long sys32_adjtimex(struct timex32 __user *utp)
 asmlinkage long sparc32_open(const char __user *filename,
 			     int flags, int mode)
 {
-	return do_sys_open(filename, flags, mode);
+	return do_sys_open(AT_FDCWD, filename, flags, mode);
 }
 
 extern unsigned long do_mremap(unsigned long addr,