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Message-ID: <Pine.LNX.4.64.0612200942060.28362@artax.karlin.mff.cuni.cz> Date: Wed, 20 Dec 2006 10:03:33 +0100 (CET) From: Mikulas Patocka <mikulas@...ax.karlin.mff.cuni.cz> To: linux-kernel@...r.kernel.org Cc: linux-fsdevel@...r.kernel.org Subject: Finding hardlinks Hi 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? Mikulas - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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