On Wed, 21 Aug 2019 04:40:15 +0000 Parav Pandit <parav@xxxxxxxxxxxx> wrote: > > -----Original Message----- > > From: Alex Williamson <alex.williamson@xxxxxxxxxx> > > Sent: Wednesday, August 21, 2019 9:51 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 > > > > On Wed, 21 Aug 2019 03:42:25 +0000 > > Parav Pandit <parav@xxxxxxxxxxxx> wrote: > > > > > > -----Original Message----- > > > > From: Alex Williamson <alex.williamson@xxxxxxxxxx> > > > > Sent: Tuesday, August 20, 2019 10:49 PM > > > > 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 > > > > > > > > On Tue, 20 Aug 2019 08:58:02 +0000 > > > > Parav Pandit <parav@xxxxxxxxxxxx> wrote: > > > > > > > > > + Dave. > > > > > > > > > > Hi Jiri, Dave, Alex, Kirti, Cornelia, > > > > > > > > > > Please provide your feedback on it, how shall we proceed? > > > > > > > > > > Short summary of requirements. > > > > > For a given mdev (mediated device [1]), there is one representor > > > > > netdevice and devlink port in switchdev mode (similar to SR-IOV > > > > > VF), And there is one netdevice for the actual mdev when mdev is probed. > > > > > > > > > > (a) representor netdev and devlink port should be able derive > > > > > phys_port_name(). So that representor netdev name can be built > > > > > deterministically across reboots. > > > > > > > > > > (b) for mdev's netdevice, mdev's device should have an attribute. > > > > > This attribute can be used by udev rules/systemd or something else > > > > > to rename netdev name deterministically. > > > > > > > > > > (c) IFNAMSIZ of 16 bytes is too small to fit whole UUID. > > > > > A simple grep IFNAMSIZ in stack hints hundreds of users of > > > > > IFNAMSIZ in drivers, uapi, netlink, boot config area and more. > > > > > Changing IFNAMSIZ for a mdev bus doesn't really look reasonable option > > to me. > > > > > > > > How many characters do we really have to work with? Your examples > > > > below prepend various characters, ex. option-1 results in ens2f0_m10 > > > > or enm10. Do the extra 8 or 3 characters in these count against IFNAMSIZ? > > > > > > > Maximum 15. Last is null termination. > > > Some udev rules setting by user prefix the PF netdev interface. I took such > > example below where ens2f0 netdev named is prefixed. > > > Some prefer not to prefix. > > > > > > > > Hence, I would like to discuss below options. > > > > > > > > > > Option-1: mdev index > > > > > Introduce an optional mdev index/handle as u32 during mdev create > > > > > time. User passes mdev index/handle as input. > > > > > > > > > > phys_port_name=mIndex=m%u > > > > > mdev_index will be available in sysfs as mdev attribute for udev > > > > > to name the mdev's netdev. > > > > > > > > > > example mdev create command: > > > > > UUID=$(uuidgen) > > > > > echo $UUID index=10 > > > > > > /sys/class/net/ens2f0/mdev_supported_types/mlx5_core_mdev/create > > > > > > > > Nit, IIRC previous discussions of additional parameters used comma > > > > separators, ex. echo $UUID,index=10 >... > > > > > > > Yes, ok. > > > > > > > > > example netdevs: > > > > > repnetdev=ens2f0_m10 /*ens2f0 is parent PF's netdevice */ > > > > > > > > Is the parent really relevant in the name? > > > No. I just picked one udev example who prefixed the parent netdev name. > > > But there are users who do not prefix it. > > > > > > > Tools like mdevctl are meant to > > > > provide persistence, creating the same mdev devices on the same > > > > parent, but that's simply the easiest policy decision. We can also > > > > imagine that multiple parent devices might support a specified mdev > > > > type and policies factoring in proximity, load-balancing, power > > > > consumption, etc might be weighed such that we really don't want to > > > > promote userspace creating dependencies on the parent association. > > > > > > > > > mdev_netdev=enm10 > > > > > > > > > > Pros: > > > > > 1. mdevctl and any other existing tools are unaffected. > > > > > 2. netdev stack, ovs and other switching platforms are unaffected. > > > > > 3. achieves unique phys_port_name for representor netdev 4. > > > > > achieves unique mdev eth netdev name for the mdev using udev/systemd > > extension. > > > > > 5. Aligns well with mdev and netdev subsystem and similar to > > > > > existing sriov bdf's. > > > > > > > > A user provided index seems strange to me. It's not really an > > > > index, just a user specified instance number. Presumably you have > > > > the user providing this because if it really were an index, then the > > > > value depends on the creation order and persistence is lost. Now > > > > the user needs to both avoid uuid collision as well as "index" > > > > number collision. The uuid namespace is large enough to mostly ignore > > this, but this is not. This seems like a burden. > > > > > > > I liked the term 'instance number', which is lot better way to say than > > index/handle. > > > Yes, user needs to avoid both the collision. > > > UUID collision should not occur in most cases, they way UUID are generated. > > > So practically users needs to pick unique 'instance number', similar to how it > > picks unique netdev names. > > > > > > Burden to user comes from the requirement to get uniqueness. > > > > > > > > Option-2: shorter mdev name > > > > > Extend mdev to have shorter mdev device name in addition to UUID. > > > > > such as 'foo', 'bar'. > > > > > Mdev will continue to have UUID. > > > > > phys_port_name=mdev_name > > > > > > > > > > Pros: > > > > > 1. All same as option-1, except mdevctl needs upgrade for newer usage. > > > > > It is common practice to upgrade iproute2 package along with the > > > > > kernel. Similar practice to be done with mdevctl. > > > > > 2. Newer users of mdevctl who wants to work with non_UUID names, > > > > > will use newer mdevctl/tools. Cons: > > > > > 1. Dual naming scheme of mdev might affect some of the existing tools. > > > > > It's unclear how/if it actually affects. > > > > > mdevctl [2] is very recently developed and can be enhanced for > > > > > dual naming scheme. > > > > > > > > I think we've already nak'ed this one, the device namespace becomes > > > > meaningless if the name becomes just a string where a uuid might be > > > > an example string. mdevs are named by uuid. > > > > > > > > > Option-3: mdev uuid alias > > > > > Instead of shorter mdev name or mdev index, have alpha-numeric > > > > > name alias. Alias is an optional mdev sysfs attribute such as 'foo', 'bar'. > > > > > example mdev create command: > > > > > UUID=$(uuidgen) > > > > > echo $UUID alias=foo > > > > > > /sys/class/net/ens2f0/mdev_supported_types/mlx5_core_mdev/create > > > > > > example netdevs: > > > > > examle netdevs: > > > > > repnetdev = ens2f0_mfoo > > > > > mdev_netdev=enmfoo > > > > > > > > > > Pros: > > > > > 1. All same as option-1. > > > > > 2. Doesn't affect existing mdev naming scheme. > > > > > Cons: > > > > > 1. Index scheme of option-1 is better which can number large > > > > > number of mdevs with fewer characters, simplifying the management > > tool. > > > > > > > > No better than option-1, simply a larger secondary namespace, but > > > > still requires the user to come up with two independent names for the > > device. > > > > > > > > > Option-4: extend IFNAMESZ to be 64 bytes Extended IFNAMESZ from 16 > > > > > to > > > > > 64 bytes phys_port_name=mdev_UUID_string > > mdev_netdev_name=enmUUID > > > > > > > > > > Pros: > > > > > 1. Doesn't require mdev extension > > > > > Cons: > > > > > 1. netdev stack, driver, uapi, user space, boot config wide changes 2. > > > > > Possible user space extensions who assumed name size being 16 > > > > > characters 3. Single device type demands namesize change for all > > > > > netdev types > > > > > > > > What about an alias based on the uuid? For example, we use 160-bit > > > > sha1s daily with git (uuids are only 128-bit), but we generally > > > > don't reference git commits with the full 20 character string. > > > > Generally 12 characters is recommended to avoid ambiguity. Could > > > > mdev automatically create an > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > > > abbreviated sha1 alias for the device? If so, how many characters > > > > should we > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > > > use and what do we do on collision? The colliding device could add > > > > enough alias characters to disambiguate (we likely couldn't re-alias > > > > the existing device to disambiguate, but I'm not sure it matters, > > > > userspace has sysfs to associate aliases). Ex. > > > > > > > > UUID=$(uuidgen) > > > > ALIAS=$(echo $UUID | sha1sum | colrm 13) > > > > > > > I explained in previous reply to Cornelia, we should set UUID and ALIAS at the > > same time. > > > Setting is via different sysfs attribute is lot code burden with no extra benefit. > > > > 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, Alex
