Neil Brown <neilb@xxxxxxx> wrote: > > On Saturday May 13, akpm@xxxxxxxx wrote: > > Paul Clements <paul.clements@xxxxxxxxxxxx> wrote: > > > > > > Andrew Morton wrote: > > > > > > > The loss of pagecache coherency seems sad. I assume there's never a > > > > requirement for userspace to read this file. > > > > > > Actually, there is. mdadm reads the bitmap file, so that would be > > > broken. Also, it's just useful for a user to be able to read the bitmap > > > (od -x, or similar) to figure out approximately how much more he's got > > > to resync to get an array in-sync. Other than reading the bitmap file, I > > > don't know of any way to determine that. > > > > Read it with O_DIRECT :( > > Which is exactly what the next release of mdadm does. > As the patch comment said: > > : With this approach the pagecache may contain data which is inconsistent with > : what is on disk. To alleviate the problems this can cause, md invalidates > : the pagecache when releasing the file. If the file is to be examined > : while the array is active (a non-critical but occasionally useful function), > : O_DIRECT io must be used. And new version of mdadm will have support for this. Which doesn't help `od -x' and is going to cause older mdadm userspace to mysteriously and subtly fail. Or does the user<->kernel interface have versioning which will prevent this? - To unsubscribe from this list: send the line "unsubscribe linux-raid" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
