> -----Original Message----- > From: Alex Williamson <alex.williamson@xxxxxxxxxx> > Sent: Friday, August 23, 2019 9:22 PM > To: Parav Pandit <parav@xxxxxxxxxxxx> > Cc: Jiri Pirko <jiri@xxxxxxxxxxx>; 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 > > On Fri, 23 Aug 2019 14:53:06 +0000 > Parav Pandit <parav@xxxxxxxxxxxx> wrote: > > > > -----Original Message----- > > > From: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > Sent: Friday, August 23, 2019 7:58 PM > > > To: Parav Pandit <parav@xxxxxxxxxxxx> > > > Cc: Jiri Pirko <jiri@xxxxxxxxxxx>; 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 > > > > > > On Fri, 23 Aug 2019 08:14:39 +0000 > > > Parav Pandit <parav@xxxxxxxxxxxx> wrote: > > > > > > > Hi Alex, > > > > > > > > > > > > > -----Original Message----- > > > > > From: Jiri Pirko <jiri@xxxxxxxxxxx> > > > > > Sent: Friday, August 23, 2019 1:42 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 03:33:30PM CEST, parav@xxxxxxxxxxxx wrote: > > > > > > > > > > > > > > > > > >> -----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? > > > > > > > > > > Ok. > > > > > > > > > > > > > Can you please confirm this scheme looks good now? I like to get > > > > patches > > > started. > > > > > > My only concern is your comment that in the event of an abbreviated > > > sha1 collision (as exceptionally rare as that might be at 12-chars), > > > we'd fail the device create, while my original suggestion was that > > > vfio-core would add an extra character to the alias. For > > > non-networking devices, the sha1 is unnecessary, so the extension > > > behavior seems preferred. The user is only responsible to provide a > > > unique uuid. Perhaps the failure behavior could be applied based on > > > the mdev device_api. A module option on mdev to specify the default > > > number of alias chars would also be useful for testing so that we > > > can set it low enough to validate the collision behavior. Thanks, > > > > > > > Idea is to have mdev alias as optional. > > Each mdev_parent says whether it wants mdev_core to generate an alias > > or not. So only networking device drivers would set it to true. > > For rest, alias won't be generated, and won't be compared either > > during creation time. User continue to provide only uuid. > > Ok > > > I am tempted to have alias collision detection only within children > > mdevs of the same parent, but doing so will always mandate to prefix > > in netdev name. And currently we are left with only 3 characters to > > prefix it, so that may not be good either. Hence, I think mdev core > > wide alias is better with 12 characters. > > I suppose it depends on the API, if the vendor driver can ask the mdev core for > an alias as part of the device creation process, then it could manage the netdev > namespace for all its devices, choosing how many characters to use, and fail > the creation if it can't meet a uniqueness requirement. IOW, mdev-core would > always provide a full sha1 and therefore gets itself out of the > uniqueness/collision aspects. > This doesn't work. At mdev core level 20 bytes sha1 are unique, so mdev core allowed to create a mdev. And then devlink core chooses only 6 bytes (12 characters) and there is collision. Things fall apart. Since mdev provides unique uuid based scheme, it's the mdev core's ownership to provide unique aliases. > > I do not understand how an extra character reduces collision, if > > that's what you meant. > > If the default were for example 3-chars, we might already have device 'abc'. A > collision would expose one more char of the new device, so we might add > device with alias 'abcd'. I mentioned previously that this leaves an issue for > userspace that we can't change the alias of device abc, so without additional > information, userspace can only determine via elimination the mapping of alias > to device, but userspace has more information available to it in the form of > sysfs links. > > > Module options are almost not encouraged anymore with other > > subsystems/drivers. > > We don't live in a world of absolutes. I agree that the defaults should work in > the vast majority of cases. Requiring a user to twiddle module options to make > things work is undesirable, verging on a bug. A module option to enable some > specific feature, unsafe condition, or test that is outside of the typical use case > is reasonable, imo. > > > For testing collision rate, a sample user space script and sample mtty > > is easy and get us collision count too. We shouldn't put that using > > module option in production kernel. I practically have the code ready > > to play with; Changing 12 to smaller value is easy with module reload. > > > > #define MDEV_ALIAS_LEN 12 > > If it can't be tested with a shipping binary, it probably won't be tested. Thanks, > It is not the role of mdev core to expose collision efficiency/deficiency of the sha1. It can be tested outside before mdev choose to use it. I am saying we should test with 12 characters with 10,000 or more devices and see how collision occurs. Even if collision occurs, mdev returns EEXIST status indicating user to pick a different UUID for those rare conditions.
