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    SubjectRe: [RFC] cgroup TODOs
    James Bottomley <James.Bottomley@HansenPartnership.com> writes:

    > On Fri, 2012-09-14 at 14:36 -0400, Aristeu Rozanski wrote:
    >> also, heard about the desire of having a device namespace instead with
    >> support for translation ("sda" -> "sdf"). If anyone see immediate use for
    >> this please let me know.
    >
    > That sounds like a really bad idea to me. We've spent ages training
    > users that the actual sd<x> name of their device doesn't matter and they
    > should use UUIDs or WWNs instead ... why should they now care inside
    > containers?

    The goal is not to introduce new the cases where people care but to
    handle cases where people do care.

    The biggest practical case of interest that I know of is if

    stat /home/myinteresintfile Device: 806h Inode: 7460974
    migration
    stat /home/myinteresintfile Device: 732h Inode: 7460974

    And an unchanging file looks like it has just become a totally different
    file on a totally different filesystem.

    I think even things like git status will care. Although how much git
    cares about the device number I don't know. I do know rsyncing a git
    tree to another directory is enough to give git conniption fits.


    So this is really about device management and handling the horrible
    things that real user space does. There is also the case that
    there are some very strong ties between the names of device nodes
    the names of sysfs files. Strong enough ties that I think you can
    strongly confuse userspace if you just happen to rename a device node.


    And ultimately this conversation is about the fact that none of this
    has been interesting enough in practice to figure out what really needs
    to be done to manage devices in containers.


    You can read the other thread if you want details. But right now it
    looks to me like the right answer is going to be building some userspace
    software and totally deprecating the device control group.

    Eric


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