[dpdk-dev] [PATCH] doc: document the new devargs syntax

[Thomas Monjalon]

17/01/2018 00:46, Gaëtan Rivet:
> On Wed, Jan 17, 2018 at 12:22:43AM +0100, Thomas Monjalon wrote:
> > 17/01/2018 00:19, Gaëtan Rivet:
> > > It might be a nitpick, but the driver specific properties might not
> > > follow the key/value pair syntax. At least for the fail-safe, a custom
> > > parsing needs to happen. I think vdev in general will need flexibility.
> > 
> > What is more flexible than key/value?
> 
> fail-safe does not need something more flexible, but different.
> It needs to define substrings describing whole devices, thus substrings
> following the aforementioned syntax.
> 
> I choose to use ( and ) as markers of beginning and end of the "special
> sub-device part that we need to skip for the moment". In the end, I need
> a way to mark the beginning and the end of a parameter. Without this,
> the next parameter would be considered as the parameter of the
> sub-device, not of the fail-safe.
> 
> = separated key/value pair does not allow for this (or with very
> convoluted additional rules to the syntax).

OK, I agree we need beginning and end markers.
I wonder whether we should consider devargs as a specific case of value.
Maybe we just want to allow using marker characters inside values.
So we can use parens or quotes to optionnaly protect the values.
But as the shell developers learned, parens are better than quotes in
the long term because it allows nested expressions.

> > > There could be a note that after the comma past the eventual
> > > "driver=xxxx" pair, the syntax is driver-specific and might not follow
> > > the equal-separated key/value pair syntax.
> > 
> > Please give an example.
> 
> bus=vdev/driver=failsafe,dev(bus=pci,id=00:02.0),fd(/some/file/)
> 
> Here, without some kind of "end-of-parameter" mark, fd() would be
> considered as a new parameter of the sub-device 00:02.0

Right.
I think an equal sign is missing between "dev" and parenthesis.

> --------------
> 
> And while I'm at it, there is an ambiguity that might need to be defined
> before the whole shebang is implemented: whether the parameters
> positions are meaningful or not. Currently some drivers might consider their
> parameters to mean different things depending on their order of appearance.
> 
> It could help to explicitly say that the order is asemic and should not
> be considered by drivers.
> 
> Why this is important: I think that depending on the new rte_devargs
> representation, it could be beneficial to have a canonical representation
> of an rte_devargs: given an arbitrary string given by users, the devargs
> could then be rewritten in a determinist way, which would help implementing
> comparison, assignment, and some other operations.
> 
> However, for this canonicalization to be possible, order needs to be
> explicitly said to be meaningless.

Good idea. I vote for meaningless ordering, except the first property
of each category, which describes the category.