Fri, Aug 23, 2019 at 04:53:06PM CEST, 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. >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 do not understand how an extra character reduces collision, if that's what you meant. Also, that breaks the naming consistency for different creation order. >Module options are almost not encouraged anymore with other subsystems/drivers. > >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 > >> Alex >> >> > > >> >> 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)... >
