Re: [PATCH] fstests: generic: Add test of seek in directories

[Christoph Hellwig <hch@infradead.org>]

Please include the mainling list for the file system you think is
buggy or at least odd.  Done now.

On Fri, Aug 28, 2026 at 09:36:10AM +1000, NeilBrown wrote:
> The test then reads the directory to find the order of the stable name,
> which should never change. It also find the "d_off" of all names.
> These d_off should be usable as a "seek" offset to find at least all
> the stable names that came after that point in the original listing.
> 
> After creating the names and finding the order, a loop which repeatly:
>   - makes random changes to unstable names
>   - checks the complete order of stable names in a new readdir
>   - checks what appears after a seek() to a randomly chosen offet
> 
> In Linux 7.2 this test always passes for xfs and ext4 but fails
> for btrfs unless we suppress renames with a "stable" name as target.
> It also fails for tmpfs.

There is no requirement where the entry for a renamed entry is placed.
Posix requires telldir/seekdir to provide a stable cookie, but how
that cookie behaves when the directory is modified is completely
undefined.  The same is true for NFS which requires basically the
same, but more stateless than local telldir/seekdir.