netdev - Re: [PATCH mlx5-next v7 0/4] Dynamically assign MSI-X vectors count

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Date:   Sat, 27 Mar 2021 13:38:05 +0100
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     Bjorn Helgaas <helgaas@...nel.org>
Cc:     Alexander Duyck <alexander.duyck@...il.com>,
        Leon Romanovsky <leon@...nel.org>,
        Jason Gunthorpe <jgg@...dia.com>,
        Keith Busch <kbusch@...nel.org>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Saeed Mahameed <saeedm@...dia.com>,
        Jakub Kicinski <kuba@...nel.org>,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-rdma@...r.kernel.org, Netdev <netdev@...r.kernel.org>,
        Don Dutile <ddutile@...hat.com>,
        Alex Williamson <alex.williamson@...hat.com>,
        "David S . Miller" <davem@...emloft.net>
Subject: Re: [PATCH mlx5-next v7 0/4] Dynamically assign MSI-X vectors count

On Fri, Mar 26, 2021 at 02:36:31PM -0500, Bjorn Helgaas wrote:
> On Fri, Mar 26, 2021 at 11:50:44AM -0700, Alexander Duyck wrote:
> 
> > I almost wonder if it wouldn't make sense to just partition this up to
> > handle flexible resources in the future. Maybe something like having
> > the directory setup such that you have "sriov_resources/msix/" and
> > then you could have individual files with one for the total and the
> > rest with the VF BDF naming scheme. Then if we have to, we could add
> > other subdirectories in the future to handle things like queues in the
> > future.
> 
> Subdirectories would be nice, but Greg KH said earlier in a different
> context that there's an issue with them [1].  He went on to say tools
> like udev would miss uevents for the subdirs [2].
> 
> I don't know whether that's really a problem in this case -- it
> doesn't seem like we would care about uevents for files that do MSI-X
> vector assignment.
> 
> [1] https://lore.kernel.org/linux-pci/20191121211017.GA854512@kroah.com/
> [2] https://lore.kernel.org/linux-pci/20191124170207.GA2267252@kroah.com/

You can only go "one level deep" on subdirectories tied to a 'struct
device' and have userspace tools know they are still there.  You can do
that by giving an attribute group a "name" for the directory.

Anything more than that just gets very very messy very quickly and I do
not recommend doing that at all.

thanks,

greg k-h