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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?

    Mikulas

    > Miklos
    >
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