Re: [Qemu-devel] [RFC 2/2] block/file-posix: verify page cache is not used

[Stefan Hajnoczi]

On Thu, Apr 19, 2018 at 10:05:47AM +0100, Dr. David Alan Gilbert wrote:
> * Stefan Hajnoczi (address@hidden) wrote:
> > This commit is for debugging only.  Do not merge it.
> > 
> > mincore(2) checks whether pages are resident.  Use it to verify that
> > page cache has been dropped.
> > 
> > You can trigger a verification failure by mmapping the image file from
> > another process and loading a byte from a page so that it becomes
> > resident.  bdrv_co_invalidate_cache() will fail while the process is
> > alive.
> 
> It doesn't seem a bad diagnostic to keep in (with a switch to activate)
> for when we're faced with some weird corruption on some weird storage
> system.

Okay.  It's very slow to mmap an entire image file and query mincore(2)
so it needs to be off by default.

Stefan

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