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    SubjectRe: st_dev:st_ino
    Mark Mielke <> writes:

    > On Sun, Jan 04, 2004 at 08:43:27PM -0500, Jeremy Maitin-Shepard wrote:
    >> Unfortunately, programs such as tar depend on inode numbers of distinct
    >> files being distinct even when the file is not open over a period of
    >> several minutes/seconds. This is needed to avoid dumping hard links
    >> more than once. Furthermore, there is no efficient way to write
    >> programs such as tar without depending on this capability. Thus, if
    >> st_ino cannot be used reliably for this purpose, it would be useful for
    >> there to be a system call for retrieving a true
    >> unique-within-the-filesystem identifier for the file.

    > We already have that: st_nlink

    > I think you mean a system call that would allow you to be certain that
    > two file descriptors refer to the same file. Then, any files with
    > st_nlink >= 2 would have to use the system call to match them up.

    In order to efficiently implement tar, it is necessary to store the
    inode numbers for files with a link count greater than 1 in a hash
    table. It would not be practical to keep open all of these files in
    order to ensure that the inode numbers remain valid. Thus, a different
    unique identifier is needed, which is unique even for files that are not

    Jeremy Maitin-Shepard
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