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    SubjectRe: [RFC PATCH v16 0/6] mm: security: ro protection for dynamic data
    On Wed, Feb 21, 2018 at 11:56:22AM +0200, Igor Stoppa wrote:
    > On 21/02/18 03:36, Dave Chinner wrote:
    > > On Tue, Feb 20, 2018 at 03:56:00PM -0800, Matthew Wilcox wrote:
    > >> On Wed, Feb 21, 2018 at 08:36:04AM +1100, Dave Chinner wrote:
    > >>> FWIW, I'm not wanting to use it to replace static variables. All the
    > >>> structures are dynamically allocated right now, and get assigned to
    > >>> other dynamically allocated pointers. I'd likely split the current
    > >>> structures into a "ro after init"
    >
    > I would prefer to use a different terminology, because, if I have
    > understood the use case, this is not exactly the same as __ro_after_init

    I want a dynamically allocated "write once" structure.

    A "write once" structure is, conceptually, is exactly the same as
    "ro after init". Implementation wise, it may be different to
    "__ro_after_init", especially when compared to static/global
    variables.

    It seems lots of people get confused when discussing concepts vs
    implementation... :)

    > >>> ......
    > >>
    > >> No, you'd do:
    > >>
    > >> struct xfs_mount_ro {
    > >> [...]
    > >> };
    >
    > is this something that is readonly from the beginning and then shared
    > among mount points or is it specific to each mount point?

    It's dynamically allocated for each mount point, made read-only
    before the mount completes and lives for the length of the mount
    point.

    > >> struct xfs_mount {
    > >> const struct xfs_mount_ro *ro;
    > >> [...]
    > >> };
    > >
    > > .... so that's pretty much the same thing :P
    >
    > The "const" modifier is a nice way to catch errors through the compiler,
    > iff the ro data will not be initialized through this handle, when it's
    > still writable.

    That's kinda implied by the const, isn't it? If we don't do it that
    way, then the compiler will throw errors....

    Cheers,

    Dave.
    --
    Dave Chinner
    dchinner@redhat.com

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