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    SubjectRe: Finding hardlinks
    > >> 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?


    > > 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().

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      Last update: 2006-12-20 17:53    [W:0.022 / U:3.504 seconds]
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