<div class="zcontentRow"> Hello Martin, This exmaple shows why we need to stop merging,Yes, It's fine since we have "stop merging" in current code. Regards Tang <div><div class="zhistoryRow" style="display:block"><div class="zhistoryDes" style="width: 100%; height: 28px; line-height: 28px; background-color: #E0E5E9; color: #1388FF; text-align: center;" language-data="HistoryOrgTxt">原始邮件</div><div id="zwriteHistoryContainer"><div class="control-group zhistoryPanel"><div class="zhistoryHeader" style="padding: 8px; background-color: #F5F6F8;"><div>发件人： ＜mwilck@suse.com＞;</div><div>收件人： ＜dm-devel@redhat.com＞;</div><div>日期：2017年02月20日 19:24</div><div>主题：Re: [dm-devel] 答复: Re: [PATCH] multipath-tools: improve processing efficiency for addition and deletion of multipath devices</div></div> <div>Hello Tang, ＞ In the second case, we know all events in the sequence have the ＞ same ＞＞ WWID; in this case I think it would be safe to filter away "remove" ＞＞ events by subsequent "add" events, ending up with "add path1| add ＞＞ path2| remove path3". But I may be overlooking something here. ＞ ＞＞ The dangerous thing if you have simultaneous remove and add events ＞ for ＞＞ the same LUN is that processing the "add" events is likely to fail ＞ in ＞＞ domap(). If you get "add path1 | remove path2", once you process ＞ "add ＞＞ path1", "path2" may not exist in the kernel any more, and "domap" ＞ will ＞＞ fail if you try to set up both; you may end up removing the map ＞＞ completely. IMHO the only safe way to process events in this ＞ situation ＞＞ is to merge the events into a single domap() call. ＞ ＞ "case 2: remove path1 |add path1 |remove path2 |add path2 |remove ＞ path3" ＞ Since the mergering is starting from the latest to the eariest ＞ uevent, so the ＞ uevent "remove path3" try to merger other uevents, if we do not stop ＞ mergering, ＞ uevent "remove path3" would merge uevent "remove path2" and uevent ＞ "remove path1". Uevent "add path2" would merge "add path1". ＞ The result is that we get two merged uevents: ＞ 1) add path2, path1 ＞ 2) remove path3, path2, path1 ＞ Then we process the merged uevents from the earlier to later, We try ＞ to ”add ＞ path2 path1“, and we would create or reload a map device with path1 ＞ and path2. ＞ Next we process ” remove path3, path2, path1“, so path1, path2 and ＞ path3 are ＞ all removed from the map device, this is wrong, the correct result ＞ is that the path1 ＞ and path2 should be still in the map device. I don't understand that. This would mean that you'd re-order "remove path1 | add path1" into "add path1| remove path1", and the same for path2. That may obviously never happen. Your "stop merging" logic forbids it, and that's fine for me for now. Regards Martin -- Dr. Martin Wilck ＜mwilck@suse.com＞, Tel. +49 (0)911 74053 2107 SUSE Linux GmbH, GF: Felix Imendörffer, Jane Smithard, Graham Norton HRB 21284 (AG Nürnberg) -- dm-devel mailing list dm-devel@redhat.com https://www.redhat.com/mailman/listinfo/dm-devel</div> </div></div></div></div> </div>