How implementation details become ABI: a case study

One of the final changes that went into the mainline kernel repository before the 3.17-rc7 release was this fix from Mikhail Efremov. It affects some low-level code within the virtual filesystem layer that manages name changes in the dentry structure — the structure that handles the mapping between file names and in-kernel inode structures. How that change came to be necessary makes a good lesson in how unintended behaviors can become part of the kernel's ABI over time.

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