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    SubjectRe: [Qemu-devel] [RFC PATCH 1/2] ivring: Add a ring-buffer driver on IVShmem
    On Wed, Jun 06, 2012 at 07:03:06AM +0800, Anthony Liguori wrote:
    > On 06/05/2012 09:10 PM, Borislav Petkov wrote:
    > >On Tue, Jun 05, 2012 at 10:01:17PM +0900, Yoshihiro YUNOMAE wrote:
    > >>This patch adds a ring-buffer driver for IVShmem device, a virtual RAM device in
    > >>QEMU. This driver can be used as a ring-buffer for kernel logging or tracing of
    > >>a guest OS by recording kernel programing or SystemTap.
    > >>
    > >>This ring-buffer driver is implemented very simple. First 4kB of shared memory
    > >>region is control structure of a ring-buffer. In this region, some values for
    > >>managing the ring-buffer is stored such as bits and mask of whole memory size,
    > >>writing position, threshold value for notification to a reader on a host OS.
    > >>This region is used by the reader to know writing position. Then, "total
    > >>memory size - 4kB" equals to usable memory region for recording data.
    > >>This ring-buffer driver records any data from start to end of the writable
    > >>memory region.
    > >>
    > >>When writing size exceeds a threshold value, this driver can notify a reader
    > >>to read data by using writel(). As this later patch, reader does not have any
    > >>function for receiving the notification. This notification feature will be used
    > >>near the future.
    > >>
    > >>As a writer records data in this ring-buffer, spinlock function is used to
    > >>avoid competing by some writers in multi CPU environment. Not to use spinlock,
    > >>lockless ring-buffer like as ftrace and one ring-buffer one CPU will be
    > >>implemented near the future.
    > >
    > >Yet another ring buffer?
    > >
    > >We already have an ftrace and perf ring buffer, can't you use one of those?
    >
    > Not to mention virtio :-)
    >
    > Why not just make a virtio device for this kind of thing?

    Yeah, that's exactly what I was thinking, why reinvent things again?

    greg k-h


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