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    SubjectRe: [PATCH] make last_inode counter in new_inode 32-bit on kernels that offer x86 compatability
    On Mon, 6 November 2006 14:50:58 -0600, Eric Sandeen wrote:
    > >
    > > While you're at it, how about making last_ino per-sb instead of
    > > system-wide? ino collisions after a wrap are just as bad as inos
    > > beyond 32bit. And this should be a fairly simple method to reduce the
    > > risk.
    > Using a global counter for multiple filesystems should actually -reduce-
    > the chance of a collision on the same filesystem, since after you wrap the
    > recycled number may go to a different filesystem.

    You're missing something. The chance for a collision _per wrap_ is
    reduced, as you said. But the number of wraps goes up. Overall and
    for large numbers, the two effects compensate each other.

    For not-so-large numbers, you can get by without the wrap by having
    this per-sb. And if you have just one or two wrapping filesystems, at
    least the others are protected. It's not much, but it is a simple
    thing to do.

    > To fix this properly, we'd need some sort of checking that the inode number
    > isn't currently being used on the filesystem in question before it's
    > assigned to the new inode.

    Absolutely. Thinking about it, iget() already has a lot of what is
    needed - except that it can block and has side effects we don't really
    want. Sounds more complicated, but I would love to be proven wrong
    here. :)


    Joern's library part 7:
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