> -----Original Message----- > From: Jiri Pirko <jiri@xxxxxxxxxxx> > Sent: Thursday, August 22, 2019 5:50 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 > > Thu, Aug 22, 2019 at 12:04:02PM CEST, parav@xxxxxxxxxxxx wrote: > > > > > >> -----Original Message----- > >> From: Jiri Pirko <jiri@xxxxxxxxxxx> > >> Sent: Thursday, August 22, 2019 3:28 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 > >> > >> 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, > >So when mdev creation is initiated, mdev core calculates the alias and if there > is any other mdev with same alias exist, it returns -EEXIST error before > progressing further. > >This way user will get to know upfront in event of collision before the mdev > device gets created. > >How about that? > > Sounds fine to me. Now the question is how many chars do we want to have. > 12 characters from Alex's suggestion similar to git? > > > > > >> 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)...
