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
