On Thu, Mar 22, 2012 at 04:15:12PM +1100, Dave Chinner wrote: > From: Dave Chinner <dchinner@xxxxxxxxxx> > > xfs_ioc_fstrim() doesn't treat the incoming offset and length > correctly. It treats them as a filesystem block address, rather than > a disk address. This is wrong because the range passed in is a > linear representation , while the filesystem block address notiation > is a sparse representation. Hence we cannot convert the range direct > to filesystem block units and then use that for calculating the > range to trim. > > While this sounds dangerous, the problem is limited to calculting > what AGs need to be trimmed. The code that calcuates the actual > ranges to trim gets the right result (i.e. only ever discards free > space), even though it uses the wrong ranges to limit what is > trimmed. Hence this is not a bug that endangers user data. Yep, I can see that the calculation of what we pass to blkdev_issue_discard() is correct and always a free extent. I am having a hard time seeing the problem related to calculating which AGs to trim. Can you give an example? > Fix this by treating the range as a disk address range and use the > appropriate functions to convert the range into the desired formats > for calculations. > > Further, fix the first free extent lookup (the longest) to actually > find the largest free extent. Currently this lookup uses a <= > lookup, which results in finding the extent to the left of the > largest because we can never get an exact match on the largest > extent. This is due to the fact that while we know it's size, we > don't know it's location and so the exact match fails and we move > one record to the left to get the next largest extent. Instead, use > a >= search so that the lookup returns the largest extent regardless > of the fact we don't get an exact match on it. > > Signed-off-by: Dave Chinner <dchinner@xxxxxxxxxx> Reviewed-by: Ben Myers <bpm@xxxxxxx> _______________________________________________ xfs mailing list xfs@xxxxxxxxxxx http://oss.sgi.com/mailman/listinfo/xfs
