On Fri, 14 Jun 2019 10:04:18 -0600 Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > On Fri, 14 Jun 2019 17:06:15 +0200 > Christophe de Dinechin <cdupontd@xxxxxxxxxx> wrote: > > > > On 14 Jun 2019, at 16:23, Alex Williamson <alex.williamson@xxxxxxxxxx> wrote: > > > > > > On Fri, 14 Jun 2019 11:54:42 +0200 > > > Christophe de Dinechin <cdupontd@xxxxxxxxxx> wrote: > > > Where is the parent/type ownership implied? > > > > I did not imply it, but I read some concern about ownership > > on your part in "they need to guess that an mdev device > > with the same parent and type is *theirs*.” (emphasis mine) > > > > I personally see no change on the “need to guess” implied > > by the fact that you run uuidgen inside the script, so > > that’s why I tried to guess what you meant. > > As I noted in the reply to the pull request, putting `uuidgen` inline > was probably a bad example. FWIW, I just sent a pull req to get rid of that inline `uuidgen` in the example. > However, the difference is that the user > has imposed the race on themselves if they invoke mdevctl like this, > they've provided a uuid but they didn't record what it is. This is the > user's problem. Pushing uuid selection into mdevctl makes it mdevctl's > problem because the interface is fundamentally broken. > > > > The intended semantics are > > > "try to create this type of device under this parent”. > > > > Agreed. Which is why I don’t see why trying to create > > with some new UUID introduces any race (as long as > > the script prints out that UUID, which I admit my patch > > entirely failed to to) > > And that's the piece that makes it fundamentally broken. Beyond that, > it seems unnecessary. I don't see this as the primary invocation of > mdevctl and the functionality it adds is trivially accomplished in a > wrapper, so what's the value? > > > >>> How do you resolve two instances of this happening in parallel and both > > >>> coming to the same conclusion which is their device. If a user wants > > >>> this sort of headache they can call mdevctl with `uuidgen` but I don't > > >>> think we should encourage it further. > > >> > > >> I agree there is a race, but if anything, having a usage where you don’t > > >> pass the UUID on the command line is a step in the right direction. > > >> It leaves the door open for the create-mdev script to do smarter things, > > >> like deferring the allocation of the mdevs to an entity that has slightly > > >> more knowledge of the global system state than uuidgen. > > > > > > A user might (likely) require a specific uuid to match their VM > > > configuration. I can only think of very niche use cases where a user > > > doesn't care what uuid they get. > > > > They do care. But I typically copy-paste my UUIDs, and then > > > > 1. copy-pasting at the end is always faster than between > > the command and other arguments (3-args case). > > > > 2. copy-pasting the output of the previous command is faster > > than having one extra step where I need to copy the same thing twice > > (2-args case). > > > > So to me, if the script is intended to be used by humans, my > > proposal makes it slightly more comfortable to use. Nothing more. > > This is your preference, but I wouldn't call it universal. Specifying > the uuid last seems backwards to me, we're creating an object so let's > first name that object. We then specify where that object should be > created and what type it has. This seems very logical to me, besides, > it's also the exact same order we use when listing mdevs :P > > Clearly there's personal preference here, so let's not arbitrarily pick > a different preference. If copy/paste order is more important to you > then submit a patch to give mdevctl real argument processing so you can > specify --uuid, --parent, --type in whatever order you want. I agree that these are personal preferences :) Real argument processing makes sense, however.
