discuss about commit 3b0f9ce: filter-mpath: get wwids from sysfs vpd_pg83

Hello List,

I remember we discussed about the mpath filter before. It looks lvm2 developers didn't trust udev and wrote hard-coded scanning actions (see commit 3b0f9cec7e999, and below function dev_is_mpath_component()) to replace mpath+udev. But in SUSE env, we had tested/ran a long time and worked fine with setting up lvm2 under obtain_device_list_from_udev=1 & external_device_info_source = "udev".

 From SUSE env, below function at least should put line 702~705 to the beginning of this function. In the other word, consulting udev first, then back off to hard-coded checks.
I don't know if the "udev+mpio+lvm2" combination in RedHat environments often encounters problems with abnormal startup. From SUSE env, it seems we do revert 3b0f9cec7e999 may got better result.

677 int dev_is_mpath_component(struct cmd_context *cmd, struct device *dev, dev_t *holder_devno)
678 {
679     struct dev_types *dt = cmd->dev_types;
680     int primary_result;
681     dev_t primary_dev;
682
683     /*
684      * multipath only uses SCSI or NVME devices
685      */
686     if (!major_is_scsi_device(dt, MAJOR(dev->dev)) && !dev_is_nvme(dt, dev))
687         return 0;
688
689     /*
690      * primary_result 2: dev is a partition, primary_dev is the whole device
691      * primary_result 1: dev is a whole device
692      */
693     if (!(primary_result = dev_get_primary_dev(dt, dev, &primary_dev)))
694         return_0;
695
696     if (_dev_is_mpath_component_sysfs(cmd, dev, primary_result, primary_dev, holder_devno)  == 1)
697         goto found;
698
699     if (_dev_in_wwid_file(cmd, dev, primary_result, primary_dev))
700         goto found;
701
702     if (external_device_info_source() == DEV_EXT_UDEV) {
703         if (_dev_is_mpath_component_udev(dev) == 1)
704             goto found;
705     }
706
707     /*
708      * TODO: save the result of this function in dev->flags and use those
709      * flags on repeated calls to avoid repeating the work multiple times
710      * for the same device when there are partitions on the device.
711      */
712
713     return 0;
714 found:
715     return 1;
716 }

Thanks,
Heming