Re: [Qemu-devel] [RFC PATCH 1/2] ivring: Add a ring-buffer driveron IVShmem

[Anthony Liguori]

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?

Regards,

Anthony Liguori

>

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