Re: [libvirt] mdevctl: A shoestring mediated device management and persistence utility

On Thu, 27 Jun 2019 19:57:04 -0600 Alex Williamson <alex.williamson(a)redhat.com&gt; wrote: > On Thu, 27 Jun 2019 15:15:02 -0600 > Alex Williamson <alex.williamson(a)redhat.com&gt; wrote: > >> On Thu, 27 Jun 2019 09:38:32 -0600 >> Alex Williamson <alex.williamson(a)redhat.com&gt; wrote: >>>> On 6/27/19 8:26 AM, Cornelia Huck wrote: >>>>> >>>>> { >>>>> "foo": "1", >>>>> "bar": "42", >>>>> "baz": { >>>>> "depends": ["foo", "bar"], >>>>> "value": "plahh" >>>>> } >>>>> } >>>>> >>>>> Something like that? >>> >>> I'm not sure yet. I think we need to look at what's feasible (and >>> easy) with jq. Thanks, >> >> I think it's not too much trouble to remove and insert into arrays, so >> what if we were to define the config as: >> >> { >> "mdev_type":"vendor-type", >> "start":"auto", >> "attrs": [ >> {"attrX":["Xvalue1","Xvalue2"]}, >> {"dir/attrY": "Yvalue1"}, >> {"attrX": "Xvalue3"} >> ] >> } >> >> "attr" here would define sysfs attributes under the device. The array >> would be processed in order, so in the above example we'd do the >> following: >> >> 1. echo Xvalue1 > attrX >> 2. echo Xvalue2 > attrX >> 3. echo Yvalue1 > dir/attrY >> 4. echo Xvalue3 > attrX >> >> When starting the device mdevctl would simply walk the array, if the >> attribute key exists write the value(s). If a write fails or the >> attribute doesn't exist, remove the device and report error. Yes, I think it makes sense to fail the startup of a device where we cannot set all attributes to the requested values. >> >> I think it's easiest with jq to manipulate arrays by removing and >> inserting by index. Also if we end up with something like above, it's >> ambiguous if we reference the "attrX" key. So perhaps we add the >> following options to the modify command: >> >> --addattr=ATTRIBUTE --delattr --index=INDEX --value=VALUE1[,VALUE2] >> >> We could handle it like a stack, so if --index is not supplied, add to >> the end or remove from the end. If --index is provided, delete that >> index or add the attribute at that index. So if you had the above and >> wanted to remove Xvalue1 but keep the ordering, you'd do: >> >> --delattr --index=0 >> --addattr --index=0 --value=Xvalue2 >> >> Which should results in: >> >> "attrs": [ >> {"attrX": "Xvalue2"}, >> {"dir/attrY": "Yvalue1"}, >> {"attrX": "Xvalue3"} >> ] Modifying by index looks reasonable; I just sent a pull request to print the index of an attribute out as well, so it is easier to specify the right attribute to modify. >> >> If we want to modify a running device, I'm thinking we probably want a >> new command and options --attr=ATTRIBUTE --value=VALUE might suffice. >> >> Do we need to support something like this for the 'start' command or >> should we leave that for simple devices and require a sequence of: >> >> # mdevctl define ... >> # mdevctl modify --addattr... >> ... >> # mdevctl start >> # mdevctl undefine >> >> This is effectively the long way to get a transient device. Otherwise >> we'd need to figure out how to have --attr --value appear multiple >> times on the start command line. Thanks, What do you think of a way to specify JSON for the attributes directly on the command line? Or would it be better to just edit the config files directly? > > This is now implemented, and yes you can specify '--addattr remove > --value 1' and mdevctl will immediately remove the device after it's > created (more power to the admin). Listing defined devices also lists Fun ;) > any attributes defined for easy inspection. It is also possible to > override the conversion of comma separated values into an array by > encoding and escaping the comma. It's a little cumbersome, but > possible in case a driver isn't fully on board with the one attribute, > one value rule of sysfs. Does this work for vfio-ap? I also still I do not have ap devices to actually test this with; but defining a device and adding attributes seems to work.