Christoph Hellwig <hch@xxxxxxxxxxxxx> writes: > On Thu, Oct 08, 2015 at 05:04:54PM +1100, Neil Brown wrote: >> Having two disks with ->raid_disk==0 does seem a little weird, but we do >> already have that in some cases. >> When you have a hot-replace going, both the original and the replacement >> have the same ->raid_disk numbers. They can be distinguished by the >> Replacement flag. >> I'm suggesting the same (sort of) for journals, and distinguish by the >> Journal flag. >> >> I did quick audit and just found setup_conf, run() and md_update_sb(). >> If you could do an audit to that would be good. I'd be surprised if you >> find many more places where Journal needs to be tested with ->raid_disk. > > Overloading positive numbers for the journal disk sounds like a bad idea > to me as it will cause a lot of confusion. I'd rather assign specific > negative values to special roles outside the actual rate. This will > require an initial audit, but give us nicely understandable rules later > on. The positive numbers are in different name-spaces: primary raid disks replacement raid disks journal disks While confusion is always possible, I think keeping these separate is not that hart. For example ->raid_disk is primarily used to place the rdev in an array after which it is the position in the array which is primarily used. The value of ->raid_disk is mostly tested only for whether it is <0 or not. I'm certainly happy to do our best to remove sources of confusion from the user-space view of these numbers (e.g. put 'journal' or 'none' in the 'slot' file, not '0' (and definitely not "-5")). But internally to the kernel it is important to remember that it isn't a primary key - and once you do that there is not much chance of confusion. Thanks, NeilBrown
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