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. > > >> 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)...
