Thu, Aug 22, 2019 at 11:42:13AM CEST, parav@xxxxxxxxxxxx wrote: > > >> -----Original Message----- >> From: Jiri Pirko <jiri@xxxxxxxxxxx> >> Sent: Thursday, August 22, 2019 2:59 PM >> To: Parav Pandit <parav@xxxxxxxxxxxx> >> Cc: Alex Williamson <alex.williamson@xxxxxxxxxx>; Jiri Pirko >> <jiri@xxxxxxxxxxxx>; David S . Miller <davem@xxxxxxxxxxxxx>; Kirti >> Wankhede <kwankhede@xxxxxxxxxx>; Cornelia Huck <cohuck@xxxxxxxxxx>; >> kvm@xxxxxxxxxxxxxxx; linux-kernel@xxxxxxxxxxxxxxx; cjia <cjia@xxxxxxxxxx>; >> netdev@xxxxxxxxxxxxxxx >> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core >> >> Wed, Aug 21, 2019 at 08:23:17AM CEST, parav@xxxxxxxxxxxx wrote: >> > >> > >> >> -----Original Message----- >> >> From: Alex Williamson <alex.williamson@xxxxxxxxxx> >> >> Sent: Wednesday, August 21, 2019 10:56 AM >> >> To: Parav Pandit <parav@xxxxxxxxxxxx> >> >> Cc: Jiri Pirko <jiri@xxxxxxxxxxxx>; David S . Miller >> >> <davem@xxxxxxxxxxxxx>; Kirti Wankhede <kwankhede@xxxxxxxxxx>; >> >> Cornelia Huck <cohuck@xxxxxxxxxx>; kvm@xxxxxxxxxxxxxxx; >> >> linux-kernel@xxxxxxxxxxxxxxx; cjia <cjia@xxxxxxxxxx>; >> >> netdev@xxxxxxxxxxxxxxx >> >> Subject: Re: [PATCH v2 0/2] Simplify mtty driver and mdev core >> >> >> >> > > > > Just an example of the alias, not proposing how it's set. In >> >> > > > > fact, proposing that the user does not set it, mdev-core >> >> > > > > provides one >> >> > > automatically. >> >> > > > > >> >> > > > > > > Since there seems to be some prefix overhead, as I ask >> >> > > > > > > about above in how many characters we actually have to >> >> > > > > > > work with in IFNAMESZ, maybe we start with 8 characters >> >> > > > > > > (matching your "index" namespace) and expand as necessary for >> disambiguation. >> >> > > > > > > If we can eliminate overhead in IFNAMESZ, let's start with 12. >> >> > > > > > > Thanks, >> >> > > > > > > >> >> > > > > > If user is going to choose the alias, why does it have to >> >> > > > > > be limited to >> >> sha1? >> >> > > > > > Or you just told it as an example? >> >> > > > > > >> >> > > > > > It can be an alpha-numeric string. >> >> > > > > >> >> > > > > No, I'm proposing a different solution where mdev-core >> >> > > > > creates an alias based on an abbreviated sha1. The user does >> >> > > > > not provide the >> >> alias. >> >> > > > > >> >> > > > > > Instead of mdev imposing number of characters on the alias, >> >> > > > > > it should be best >> >> > > > > left to the user. >> >> > > > > > Because in future if netdev improves on the naming scheme, >> >> > > > > > mdev will be >> >> > > > > limiting it, which is not right. >> >> > > > > > So not restricting alias size seems right to me. >> >> > > > > > User configuring mdev for networking devices in a given >> >> > > > > > kernel knows what >> >> > > > > user is doing. >> >> > > > > > So user can choose alias name size as it finds suitable. >> >> > > > > >> >> > > > > That's not what I'm proposing, please read again. Thanks, >> >> > > > >> >> > > > I understood your point. But mdev doesn't know how user is >> >> > > > going to use >> >> > > udev/systemd to name the netdev. >> >> > > > So even if mdev chose to pick 12 characters, it could result in collision. >> >> > > > Hence the proposal to provide the alias by the user, as user >> >> > > > know the best >> >> > > policy for its use case in the environment its using. >> >> > > > So 12 character sha1 method will still work by user. >> >> > > >> >> > > Haven't you already provided examples where certain drivers or >> >> > > subsystems have unique netdev prefixes? If mdev provides a >> >> > > unique alias within the subsystem, couldn't we simply define a >> >> > > netdev prefix for the mdev subsystem and avoid all other >> >> > > collisions? I'm not in favor of the user providing both a uuid >> >> > > and an alias/instance. Thanks, >> >> > > >> >> > For a given prefix, say ens2f0, can two UUID->sha1 first 9 >> >> > characters have >> >> collision? >> >> >> >> I think it would be a mistake to waste so many chars on a prefix, but >> >> 9 characters of sha1 likely wouldn't have a collision before we have >> >> 10s of thousands of devices. Thanks, >> >> >> >> Alex >> > >> >Jiri, Dave, >> >Are you ok with it for devlink/netdev part? >> >Mdev core will create an alias from a UUID. >> > >> >This will be supplied during devlink port attr set such as, >> > >> >devlink_port_attrs_mdev_set(struct devlink_port *port, const char >> >*mdev_alias); >> > >> >This alias is used to generate representor netdev's phys_port_name. >> >This alias from the mdev device's sysfs will be used by the udev/systemd to >> generate predicable netdev's name. >> >Example: enm<mdev_alias_first_12_chars> >> >> What happens in unlikely case of 2 UUIDs collide? >> >Since users sees two devices with same phys_port_name, user should destroy recently created mdev and recreate mdev with different UUID? Driver should make sure phys port name wont collide, in this case that it does not provide 2 same attrs for 2 different ports. Hmm, so the order of creation matters. That is not good. >> >> >I took Ethernet mdev as an example. >> >New prefix 'm' stands for mediated device. >> >Remaining 12 characters are first 12 chars of the mdev alias. >> >> Does this resolve the identification of devlink port representor? >Not sure if I understood your question correctly, attemping to answer below. >phys_port_name of devlink port is defined by the first 12 characters of mdev alias. >> I assume you want to use the same 12(or so) chars, don't you? >Mdev's netdev will also use the same mdev alias from the sysfs to rename netdev name from ethX to enm<mdev_alias>, where en=Etherenet, m=mdev. > >So yes, same 12 characters are use for mdev's netdev and mdev devlink port's phys_port_name. > >Is that what are you asking? Yes. Then you have 3 chars to handle the rest of the name (pci, pf)...
