lkml.org 
[lkml]   [2006]   [Dec]   [20]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: Finding hardlinks
From
Date
> >> I've came across this problem: how can a userspace program (such as for
> >> example "cp -a") tell that two files form a hardlink? Comparing inode
> >> number will break on filesystems that can have more than 2^32 files (NFS3,
> >> OCFS, SpadFS; kernel developers already implemented iget5_locked for the
> >> case of colliding inode numbers). Other possibilities:
> >>
> >> --- compare not only ino, but all stat entries and make sure that
> >> i_nlink > 1?
> >> --- is not 100% reliable either, only lowers failure probability
> >> --- create a hardlink and watch if i_nlink is increased on both files?
> >> --- doesn't work on read-only filesystems
> >> --- compare file content?
> >> --- "cp -a" won't then corrupt data at least, but will create
> >> hardlinks where they shouldn't be.
> >>
> >> Is there some reliable way how should "cp -a" command determine that?
> >> Finding in kernel whether two dentries point to the same inode is trivial
> >> but I am not sure how to let userspace know ... am I missing something?
> >
> > The stat64.st_ino field is 64bit, so AFAICS you'd only need to extend
> > the kstat.ino field to 64bit and fix those filesystems to fill in
> > kstat correctly.
>
> There is 32-bit __st_ino and 64-bit st_ino --- what is their purpose? Some
> old compatibility code?

Yes.

> > SUSv3 requires st_ino/st_dev to be unique within a system so the
> > application shouldn't need to bend over backwards.
>
> I see but kernel needs to be fixed for that. Would patches for changing
> kstat be accepted?

I don't see any problems with changing struct kstat. There would be
reservations against changing inode.i_ino though.

So filesystems that have 64bit inodes will need a specialized
getattr() method instead of generic_fillattr().

Miklos
-
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/

\
 
 \ /
  Last update: 2006-12-20 17:53    [from the cache]
©2003-2011 Jasper Spaans