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? >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? I assume you want to use the same 12(or so) chars, don't you?
