On 11/17/17 2:48 PM, Ross Zwisler wrote: > On Fri, Nov 17, 2017 at 02:39:07PM -0600, Eric Sandeen wrote: >> On 11/17/17 2:25 PM, Ross Zwisler wrote: >>> Add a new 'log_writes' command to xfs_io so that we can add dm-log-writes >>> log marks via the external 'dmsetup' executable. It's helpful to allow >>> users of xfs_io to adds these marks from within xfs_io instead of waiting >>> until after xfs_io exits because then they are able to replay the >>> dm-log-writes log up to immediately after another xfs_io operation such as >>> mwrite. This isolates the log replay from other operations that happen as >>> part of xfs_io exiting (file handles being closed, mmaps being torn down, >>> etc.). This also allows users to insert multiple marks between different >>> xfs_io commands. >>> >>> Signed-off-by: Ross Zwisler <ross.zwisler@xxxxxxxxxxxxxxx> >>> Suggested-by: Dave Chinner <david@xxxxxxxxxxxxx> >> >> Without reviewing in detail, what is the advantage of wrapping dmsetup >> into xfs_io? My first inclination is that there is none at all, and >> xfstests can call dmsetup as easily as they can call xfs_io. No? >> >> -Eric > > I commented on this a bit in the changelog for the 2nd patch: > > It's helpful to allow users of xfs_io to adds these marks from within xfs_io > instead of waiting until after xfs_io exits because then they are able to > replay the dm-log-writes log up to immediately after another xfs_io operation > such as mwrite. This isolates the log replay from other operations that > happen as part of xfs_io exiting (file handles being closed, mmaps being torn > down, etc.). This also allows users to insert multiple marks between > different xfs_io commands. > > I agree that the shell-out to dmsetup isn't awesome... For the current test I > have written I think we can get away with just assuming that the xfs_io exit > stuff won't interact too heavily with the dm-log-writes log, and we could > potentially move the dmsetup call back into the fstest. This is how I > initially had it, and moved it into the C program via shell-out in response to > Amir's feedback: Sorry, terrible of me to not have read that. :( Ok, so next question - DM_TARGET_MSG seems to be public, can we just invoke the ioctl directly instead of shelling out to dmsetup? I'm checking w/ the dm folks too, to make sure that's expected to work. As long as the use isn't too tricky it seems like that might be better. -Eric -- To unsubscribe from this list: send the line "unsubscribe linux-xfs" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
