Hi Alasdair, Thanks for your feedback. MikeC and mikeand, feel free to add. On Tue, 2008-04-29 at 15:56 +0100, Alasdair G Kergon wrote: > On Thu, Apr 24, 2008 at 04:03:11PM +0000, James Bottomley wrote: > > This patch converts dm-mpath to scsi hw handlers. It does > > not add any new functionality and old behaviors and userspace > > tools work as is except we use the safe clariion default instead > > of using the userspace setting. > > OK. Comments from my first line-by-line reading of this. > > Firstly, the patch header is rather too brief for my liking - the patch > does make some subtle functional changes that ought to be commented upon > to explain to people why they are being made. (I would have preferred will do. > this patch to have been broken up into smaller ones in a manner that > made the functional changes more obvious i.e. separated from the code > reorganisation.) will do. > > 1. Currently the supplied hw_handler name is validated at table load > time so userspace cannot create a device using a non-existent > hw_handler. After this patch it looks as if that validation is delayed > until something starts to access the device - and then the paths simply > get failed, a new failure mode for the userspace tools to handle. Is > that change hard to avoid or was it judged not worth the effort to leave > things as they were and perform as much validation / resource allocation > as possible up front? For the current implementation, initialization of the scsi_dh specific data need to happen when we see the device the very first time (for prep_fn() and check_sense() to be useful). We cannot wait till multipath comes along, and the device specific data will exist till the device is removed, hence there is no need to hold onto a reference for each device for mulipath's sake. But, I agree with your point that the failure should happen early. Will add a scsi_dh_handler_exist(name) function to make sure that the module is available at the time of table load. What do you think ? > > 2. parse_hw_handler() now ignores hw_handler arguments. > Please add a comment to explain that or perhaps log a warning message if > any are supplied. will do > BTW r looks superfluous now: > > if (read_param(_params, shift(as), &hw_argc, &ti->error)) > return -EINVAL; will fix. > > 3. The dmsetup table output has changed - it no longer matches the input > in the case where arguments got ignored. I don't think this matters > (unlike a similar issue we had with crypt), but it should be noted in > comments inline. will add comments. > > 4. /* Fields used by hardware handler usage */ > Comment doesn't add anything - drop it? > ok. > 5. char *hw_handler_name; > const? will fix. > > 6. The code now assumes all hw_handlers have a pg_init function: in > practice this is likely to be the case. Does that permit further > simplification of some of the logic? will look into it. > > 7. I note that the 'bypassed' argument to the pg_init function has been > dropped - presumably as none of the existing handlers made any use of > it. Yes, none of the hardware handlers used it. > > 8. A new workqueue is introduced without comment. Will add. > Which of the changes means we need it now? I do not understand this comment. > What's the reason it's not single-threaded (and per-device)? Per device might be an overkill. Will do single-threaded. > Is there a clearer name than "khwhandlerd" - > something that tells people it's connected with multipath, and how does kmpath_handlerd sound ? > can the name of the struct workqueue_struct variable match this? will fix. > Previously the hw_handler pg_init function was required to return > immediately. Can its replacement scsi_dh_activate() block (but not in a > way that could deadlock of course)? Yes, scsi_dh_activate() can block. But, at the dm-level, it is indifferent, due to the usage of the workqueue. > Should some of its functionality be > got out of the way at initialisation time within multipath_ctr()? You mean hardware handler specific initialization ? It happens when the device is found. We do not want to wait till multipath comes along. > > 9. What does m->path_to_activate give us that m->current_pgpath > doesn't? I guess none. Was just sticking with the original interface as it was handed off to an asynchronous thread. If it won't matter, I will fix it to use it directly from the multipath data structure. > > 10. Is activate_passive_path() an accurate function name? Is the > supplied path argument always 'passive'? May be not always. Will change it activate_path(). > > 11. Where has the use of pg_init_retries gone? Oops.. will fix. > > I still need to check the updated state machine logic and associated > locking once we have a final version of this patch. > > Alasdair -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
