On Mon, Feb 12, 2018 at 05:18:02PM -0600, Benjamin Marzinski wrote: > It is the DM_EXISTS_FLAG. It's defined in libdm/ioctl/libdm-iface.c in > the lvm2 source. It is unconditionally set on all dm control ioctls > from libdevmapper by _do_dm_ioctl() (also in libdm/ioctl/libdm-iface.c). > I don't know the reason for this. I don't see anything that uses it in > driver/md/dm-ioctl.c, and I see that line in the libdm source has a > /* FIXME */ next to it. On the other hand, all I'm trying to do here is > run the same ioctl that libdevmapper would if it supported this command, > and there may well be a reason for it that I'm missing. DM_EXISTS_FLAG indicates that the device the ioctl referenced exists. If you performed certain queries and the device was not found, you got a successful return but without this flag. In the dim and distant past this flag was handled kernel-side. Later, we dropped it but left that userspace code emulating it. The FIXMEs were just saying that the library code could be cleaned up too one day. Ref. https://lwn.net/Articles/38512/ Alasdair -- dm-devel mailing list dm-devel@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/dm-devel
