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Re: [libvirt] [PATCHv3 18/19] blockjob: refactor qemu disk chain permission grants

On 10/18/2012 12:50 PM, Laine Stump wrote:
> On 10/17/2012 06:30 PM, Eric Blake wrote:
>> Previously, snapshot code did its own permission granting (lock
>> manager, cgroup device controller, and security manager labeling)
>> inline.  But now that we are adding block-commit and block-copy
>> which also have to change permissions, it's better to reuse
>> common code for the task.  While snapshot should fall back to
>> no access if read-write access failed, block-commit will want to
>> fall back to read-only access.  The common code doesn't know
>> whether failure to grant read-write access should revert to no
>> access (snapshot, block-copy) or read-only access (block-commit).
>> This code can also be used to revoke access to unused files after
>> block-pull.

> ACK, with qualifying remarks from the review of the previous version of
> the patch (PATCHv2 17/16)

I'm adding this to the commit message:

    It might be nice to clean things up in a future patch by adding
    new functions to the lock manager, cgroup manager, and security
    manager that takes a single file name and applies context of a
    disk to that file, rather than the current semantics of applying
    context to the entire chain already associated to a disk.  That
    way, we could avoid the games this patch plays of temporarily
    swapping out the disk->src and related fields of the disk.  But
    that would involve more code changes, so this patch really is
    the smallest hack for doing the necessary work; besides, this
    patch is more or less code motion (the hack was already employed
    by the snapshot creation code, we are just making it reusable).

Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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