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    SubjectRe: [patch 4/8] fs, exportfs: Add export_encode_inode_fh helper
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    Pavel Emelyanov <xemul@parallels.com> writes:

    > On 08/20/2012 11:32 PM, J. Bruce Fields wrote:
    >> On Mon, Aug 20, 2012 at 11:06:06PM +0400, Cyrill Gorcunov wrote:
    >>> On Mon, Aug 20, 2012 at 02:32:25PM -0400, J. Bruce Fields wrote:
    >>>> On Mon, Aug 20, 2012 at 08:33:38PM +0400, Cyrill Gorcunov wrote:
    >>>>> On Mon, Aug 20, 2012 at 07:49:23PM +0530, Aneesh Kumar K.V wrote:
    >>>>>> Cyrill Gorcunov <gorcunov@openvz.org> writes:
    >>>>>>
    >>>>>>> To provide fsnotify object inodes being watched without
    >>>>>>> binding to alphabetical path we need to encode them with
    >>>>>>> exportfs help. This patch adds a helper which operates
    >>>>>>> with plain inodes directly.
    >>>>>>
    >>>>>> doesn't name_to_handle_at() work for you ? It also allows to get a file
    >>>>>> handle using file descriptor.
    >>>>>
    >>>>> Hi, sorry for dealy. Well, the last idea is to get rid of this helper,
    >>>>> I've sent out an updated version where ino+dev is only printed.
    >>>>
    >>>> I don't understand how ino and dev are useful to you, though, if you're
    >>>> still hoping to be able to look up inodes using this information later
    >>>> on.
    >>>
    >>> Hi Bruce, I believe having ino+dev is better than nothing. Otherwise we
    >>> simply have no clue which targets are bound to inotify mark. Sometime
    >>> (!) we can try to generate fhandle in userspace from this ino+dev bundle
    >>> and then open the target file.
    >>
    >> That's insufficient to generate a filehandle in general.
    >
    > Yes, sure, but for live migration having inode and device is enough and that's why.
    > We can use two ways of having a filesystem on the target machine in the same
    > state (from paths points of view) as it was on destination one:
    >
    > 1. copy file tree in a rsync manner
    > 2. copy a virtual disk image file
    >
    > In the 1st case we can map inode number to path easily, since we iterate over a filesystem
    > anyway. I agree, that rsync is not perfect for migration but still.
    >
    > In the 2nd case we can generate filehandle out of an inode number only since we _do_ know
    > that inode will not get reused.

    If you are going to to use open_by_handle, then that handle is not
    sufficient right ? Or do you have open_by_inode ? as part of c/r ?

    >
    >
    > However, if you have some better ideas on what information about inode should be exported
    > to the userspace please share.
    >

    Why not use name_to_handle(fd,...) and open_by_handle(handle,..) ?


    >> (Also: there's the usual inode-number aliasing problem: the inode number
    >> could get reused by another file. Unless you know the file is being
    >> held open the whole time.)
    >>

    -aneesh



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