On Mon, Nov 13, 2023 at 02:52:39PM +0100, Peter Rajnoha wrote: > On 11/13/23 12:52, Martin Wilck wrote: > > I can't stress enough that this is *the only mechanism* that works > > correctly. udev serves as central hub to retrieve device properties > > from, and this is how it ought to be. > > Indeed, that was exactly one of the primary reasons the > 'external_device_info_source="udev"' was added. Reimplementing other > subsystem's logic is wrong because there's always some intrinsic logic > there that may be omitted. Sooner or later, such approach will fail. > > I agree with you here. > > If not sharing information through udev due to various kinds of hatred > about this part of the system, then alternatively, at least, calling a > multipath library function from LVM to do the job. Hi, a number of things haven't been mentioned or noticed: - In general, it's old versions of lvm that we're discussing here. Current lvm uses system.devices by default, where none of this is relevant. We can just turn off a number of filters when system.devices is in use, including filter-mpath and filter-md. It may still be interesting to look at improvements, but the context for that is older stable, released versions. - In RHEL8 (no system.devices by default, and some older systemd/udev), lvm can't touch udev without causing timeouts booting with many devices. Nothing I tried apart from reading wwids would help. Boot timeouts were a big support burden, and the motivation for the changes. (All of this added motivation for system.devices.) - I tried many things before reading wwids, including asking for a multipath lib API for reading the wwids. The provided API that I tried also used udev, so it was no better. I'd still prefer to use an API to check a wwid and avoid reading /etc/multipath/wwids directly. Reading wwids looked like the least worst practical solution. I consider it a temporary hack/workaround until system.devices eliminates the issue. - When making the changes to avoid udev by default, I made a subtle change to the meaning of external_device_info_source=udev. I made that info supplementary to the native info rather than an alternative to the native info. The idea was: why not use all the info we have available? However, for filter-mpath, the supplementary approach will be a problem if reading wwids gives a false positive. - To make filter-mpath use udev info, and prevent lvm from using wwids, you can set external_device_info_source=udev and multipath_wwids_file="". I think this will be an effective way to avoid any false positive problems from native detection. Dave
