Autore: Marlon Nunes Data: To: Jude Nelson CC: dng Oggetto: Re: [DNG] [Dng] vdev status update: device properties and udev
compatibility
Thank you very much!
On 2015-06-25 02:04, Jude Nelson wrote: > Hey everyone,
>
> After a longer-than-expected development cycle, I have the latest news
> for vdev.
>
> The TL;DR is that vdev has gained enough infrastructure to generate
> the information that normally gets put in /run/udev. This is
> important for most libudev clients, because this information gets used
> to detect and enumerate hardware. It's the way the X server detects
> input devices via udev, for example.
>
> This is still being heavily tested, and is not complete, but I am
> please to report that:
>
> * vdev now tracks device properties and device tags, under
> /dev/metadata/$DEVPATH/properties and /dev/metadata/$DEVPATH/tags/,
> respectively. They are added by shell library subroutines available
> to vdev's helpers (in subr.sh).
>
> * vdev now uses the same hardware database as udev to report
> human-curated hardware properties (such as human-readable vendor
> strings). To keep things simple, vdev comes with a script that
> generates a squashfs filesystem image from the *.hwdb files installed
> to /lib/udev/hwdb.d and /etc/udev/hwdb.d. This is our alternative to
> systemd's/udevd's mmap()-able on-disk hwdb trie. The filesystem image
> itself gets mounted to /dev/metadata/hwdb by the pre-seed script, and
> vdev now comes with a helper tool (hwdb.sh) that can use a combination
> of a modalias string, a devpath, a subsystem path, and some sysfs
> information to look up the device properties.
>
> * vdev now comes with a "udev-compat.sh" helper script that reads
> vdev's /dev/metadata/ directory and hardware database in order to
> generate /dev/metadata/udev, which is meant to be symlinked to
> /run/udev. This lets the udev_enumerate API detect and enumerate
> devices by tags and properties. It is important to emphasize that
> this helper is logically isolated from the rest of vdev--vdev gets
> along just fine without it (since all udev-isms are contained by this
> helper), so if you don't need /run/udev, you can safely disable this
> helper script.
>
> * Disk property detection has been significantly improved, and is much
> closer to how udev does it (including adding support for querying a
> disk's parent device's properties, which is necessary to handle
> partitions properly). Thanks to Didier for working with me on this!
> In time, it will also work the busybox tools, but I am still working
> on getting busybox's blkid to work here (specifically, we need the
> "-p" flag to work in order to get low-level partition table
> information and filesystem metadata).
>
> There is of course more work to be done on this, but the next big
> milestone (my next goal) will be to boot to X with vdevd, without
> having to generate an xorg.conf. I have not tried this yet, and I do
> not expect it to work as of the latest commit, but I believe that all
> the necessary infrastructure is in place to begin the painstaking
> process of ensuring that vdev detects enough of the host's devices'
> properties for commonly-used libudev clients work as they did with
> udev. This will confirm that we generate enough of /run/udev/ for
> alpha.
>
> Thanks,
> Jude
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