Re: [RFC 07/22] dm: blk: add UCLASS_PARTITION

Simon Glass
2021-11-05T02:06:15Z

Hi,

On Tue, 2 Nov 2021 at 01:43, Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
>
>
>
> On 11/1/21 03:14, Simon Glass wrote:
> > Hi Takahiro,
> >
> > On Sun, 31 Oct 2021 at 19:52, AKASHI Takahiro
> > <takahiro.akashi@linaro.org> wrote:
> >>
> >> On Sun, Oct 31, 2021 at 07:15:17PM -0600, Simon Glass wrote:
> >>> Hi Takahiro,
> >>>
> >>> On Sun, 31 Oct 2021 at 18:36, AKASHI Takahiro
> >>> <takahiro.akashi@linaro.org> wrote:
> >>>>
> >>>> On Sat, Oct 30, 2021 at 07:45:14AM +0200, Heinrich Schuchardt wrote:
> >>>>>
> >>>>>
> >>>>> Am 29. Oktober 2021 23:17:56 MESZ schrieb Simon Glass <sjg@chromium.org>:
> >>>>>> Hi,
> >>>>>>
> >>>>>> On Fri, 29 Oct 2021 at 13:26, Heinrich Schuchardt <xypron.glpk@gmx.de> wrote:
> >>>>>>>
> >>>>>>>
> >>>>>>>
> >>>>>>> Am 29. Oktober 2021 08:15:56 MESZ schrieb AKASHI Takahiro <takahiro.akashi@linaro.org>:
> >>>>>>>> On Fri, Oct 29, 2021 at 06:57:24AM +0200, Heinrich Schuchardt wrote:
> >>>>>>>>>
> >>>>>>>>>
> >>>>>>>>>> I agree with Heinrich that we are better to leave BLK as it is, both
> >>>>>>>>>> in name and meaning. I think maybe I am missing the gist of your
> >>>>>>>>>> argument.
> >>>>>>>>>>
> >>>>>>>>>> If we use UCLASS_PART, for example, can we have that refer to both s/w
> >>>>>>>>>> and h/w partitions, as Herinch seems to allude to below? What would
> >>>>>>>>>> the picture look like the, and would it get us closer to agreement?
> >>>>>>>>>
> >>>>>>>>> In the driver model:
> >>>>>>>>>
> >>>>>>>>> A UCLASS is a class of drivers that share the same interface.
> >>>>>>>>> A UDEVICE is a logical device that belongs to exactly one UCLASS and is
> >>>>>>>>> accessed through this UCLASS's interface.
> >>>>>>>>
> >>>>>>>> Please be careful about "accessed through" which is a quite confusing
> >>>>>>>> expression. I don't always agree with this view.
> >>>>>>>>
> >>>>>>>>> A hardware partition is an object that exposes only a single interface
> >>>>>>>>> for block IO.
> >>>>>>>>>
> >>>>>>>>> A software partition is an object that may expose two interfaces: one
> >>>>>>>>> for block IO, the other for file IO.
> >>>>>>>>
> >>>>>>>> Are you talking about UEFI world or U-Boot?
> >>>>>>>> Definitely, a hw partitions can provide a file system
> >>>>>>>> if you want.
> >>>>>>>> It's a matter of usage.
> >>>>>>>>
> >>>>>>>> I remember that we had some discussion about whether block devices
> >>>>>>>> on UEFI system should always have a (sw) partition table or not.
> >>>>>>>> But it is a different topic.
> >>>>>>>>
> >>>>>>>>> The UEFI model does not have a problem with this because on a handle you
> >>>>>>>>> can install as many different protocols as you wish. But U-Boot's driver
> >>>>>>>>> model only allows a single interface per device. Up to now U-Boot has
> >>>>>>>>> overcome this limitation by creating child devices for the extra interfaces.
> >>>>>>>>
> >>>>>>>>> We have the following logical levels:
> >>>>>>>>>
> >>>>>>>>> Controller | Block device | Software Partition| File system
> >>>>>>>>> ----------------+--------------+-------------------+------------
> >>>>>>>>> NVMe Drive | Namespace | Partition 1..n | FAT, EXT4
> >>>>>>>>> ATA Controller | ATA-Drive | |
> >>>>>>>>> SCSI Controller | LUN | |
> >>>>>>>>> MMC Controller | HW-Partition | |
> >>>>>>>>> MMC Controller | SD-Card | |
> >>>>>>>>> USB-Node | USB-Drive | |
> >>>>>>>>>
> >>>>>>>>> In the device tree this could be modeled as:
> >>>>>>>>>
> >>>>>>>>> |-- Controller (UCLASS_CTRL)
> >>>>>>>>> | |-- Block device / HW Partition (UCLASS_BLK) (A)
> >>>>>>>>> | | |-- Partition table (UCLASS_PARTITION_TABLE) (B)
> >>>>>>>>> | | |-- Software Partition (UCLASS_BLK)
> >>>>>>>>> | | |-- File system (UCLASS_FS)
> >>>>>>>>> | |
> >>>>>>>>> | |-- Block device (UCLASS_BLK)
> >>>>>>>>> | |-- File system (UCLASS_FS)
> >>>>>>>>
> >>>>>>>> I don't know why we expect PARTITION_TABLE and FS to appear in DM tree.
> >>>>>>>> What is the benefit?
> >>>>>>>> (A) and (B) always have 1:1 relationship.
> >>>>>>>
> >>>>>>> No. You can have a bare device without a partition table.
> >>>>>>
> >>>>>> I can have a DOS partition that covers the whole device, without a
> >>>>>> partition table. This is supported in U-Boot and Linux.
> >>>>>>
> >>>>>>>
> >>>>>>> We have several partition table drivers: DOS, GPT, OSX, ... . In future we should also have one for the NOR Flash partitions. All of these drivers have a common interface. As the partition table type is mostly independent of the block device type we should use separate uclasses and udevices.
> >>>>>>>
> >>>>>>>> I also remember that you claimed that not all efi objects(handles and
> >>>>>>>> protocols like SIMPE_FILE_SYSTEM_PROTOCOL) need to have corresponding
> >>>>>>>> U-Boot counterparts in our 2019 discussion.
> >>>>>>>>
> >>>>>>>> If we *need* PARTITION_TALBLE, why don't we have HW_PARTITION_TABLE,
> >>>>>>>> which should support other type of hw partitions as well?
> >>>>>>>
> >>>>>>> How hardware partitions, LUNs, ATA drives are enumerated is specific to the type of controller while the type of software partition table is independent of the block device.
> >>>>>>>
> >>>>>>>>
> >>>>>>>> |-- eMMC controller (UCLASS_MMC)
> >>>>>>>> | |-- eMMC device1 / Physical media (UCLASS_HW_PARTITION_TABLE?)
> >>>>>>>> | |-- Block device / HW Partition:user data (UCLASS_BLK)
> >>>>>>>> | | |-- Partition table (UCLASS_PARTITION_TABLE)
> >>>>>>>> | | |-- Software Partition (UCLASS_BLK)
> >>>>>>>> | | |-- File system (UCLASS_FS)
> >>>>>>>> | |
> >>>>>>>> | |-- Block device / HW Partition:boot0 (UCLASS_BLK)
> >>>>>>>> | |-- Block device / HW Partition:boot1 (UCLASS_BLK)
> >>>>>>>> ...
> >>>>>>>> | |-- eMMC device2 / Physical media (UCLASS_HW_PARTITION_TABLE?)
> >>>>>>>>
> >>>>>>>> |-- scsi controller (UCLASS_SCSI)
> >>>>>>>> | |-- scsi disk / Physical media (UCLASS_HW_PARTITION_TABLE?)
> >>>>>>>> | |-- scsi LUN1 (UCLASS_HW_PARTITION_TABLE?)
> >>>>>>>> | | |-- Partition table (UCLASS_PARTITION_TABLE)
> >>>>>>>> | | |-- Software Partition (UCLASS_BLK)
> >>>>>>>> | |-- scsi LUN2 (UCLASS_HW_PARTITION_TABLE?)
> >>>>>>>> ...
> >>>>>>>>
> >>>>>>>> (Here I ignored scsi buses/channels which make things more complicated.)
> >>>>>>>>
> >>>>>>>> This kind of complex hierarchy doesn't benefit anybody.
> >>>>>>>
> >>>>>>> All these levels exist already. We simply do not model them yet in the DM way.
> >>>>>>>
> >>>>>>> The device tree depth is the outcome of the udevice exposing always only a single interface defined by the uclass.
> >>>>>>>
> >>>>>>> The UEFI design allows installing multiple protocol interfaces on a single handle. This may result in simpler device trees in some cases.
> >>>>>>
> >>>>>> Yes, the complexity has to go somewhere. With driver model I chose to
> >>>>>> have a single interface per uclass, since it is simpler to understand,
> >>>>>> no need to request a protocol for a device, etc.
> >>>>>>
> >>>>>> Our current setup is similar to this
> >>>>>>
> >>>>>> |-- Controller (UCLASS_MMC)
> >>>>>> | |-- Block device (UCLASS_BLK) - 'usual' HW partition
> >>>>>> | |-- Block device (UCLASS_BLK) - e.g. for a different HW partition*
> >>>>>>
> >>>>>> * although I don't think the MMC code actually supports it - SCSI does though
> >>>>>>
> >>>>>> We want to add devices for the partition table and the filesystem, so could do:
> >>>>>>
> >>>>>> |-- Controller (UCLASS_MMC)
> >>>>>> | |-- Block device (UCLASS_BLK) - 'usual' HW partition (the whole device)
> >>>>>> | | |-- Partition table (UCLASS_PART) - DOS partition (or EFI)
> >>>>>> | | | |-- Block device (UCLASS_BLK) - partition 1
> >>>>>> | | | | |-- Filesystem (UCLASS_FS) - DOS filesystem
> >>>>>> | | | |-- Block device (UCLASS_BLK) - partition 2
> >>>>>> | | | | |-- Filesystem (UCLASS_FS) - ext5 filesystem
> >>>>>> | |-- Block device (UCLASS_BLK) - e.g. for a different HW
> >>>>>> partition (the whole device)
> >>>>>>
> >>>>>> This is similar to Heinrich's, but without the top-level
> >>>>>> UCLASS_HW_PARTITION_TABLE which I am not sure is necessary.
> >>>>>
> >>>>> Are further MMC hw partitions, multiple SCSI LUNs and multiple NVME namespaces already treated as separate BLK devices?
> >>>>
> >>>> Yes.
> >>>> What I meant to say is that, if we don't need a partition table 'udevice'
> >>>> for hw partitions, we don't need such a device for sw partitions neither.
> >>>>
> >>>> Meanwhile, what about UCLASS_FS? Why do we need this?
> >>>
> >>> We don't need it for our current discussion, but if we want to 'open'
> >>> the filesystem and keep the metadata around, rather than reading it
> >>> again every time we access a file, we might find it useful. Open files
> >>> could be children of the FS uclass, perhaps, if we go a step further
> >>> and create devices for them.
> >>
> >> Do you want to invent linux-like mount-point concepts or procfs?
> >> I remember that you didn't want to have child nodes under BLK devices.
> >> I'm getting confused about our goal.
> >
> > I think we are all a bit unsure.
> >
> > I think BLK devices can have children, sorry if I said the wrong thing
> > somewhere along the way. For example, a partition would be under a BLK
> > device, or a FS.
> >
> >> What should DM represent in U-Boot world?
> >
> > That is what we are trying to figure out.
> >
> > I think the minimum is to have a a way to represent partitions (s/w
> > and hw/). As I understand it, that's what we've been discussing.
>
> The discovery of hardware partitions is specific to the block device
> controller SCSI/MMC/ATA/NVMe. We currently do not provide any
> manipulation commands to create hardware partitions (e.g. NVMe
> namespaces, SCSI LUNs). This is why extracting a uclass for hardware
> partitions does not seem necessary.

I can see the reasoning here. It might not stand the test of time but
how about we go with it for now? For MMC hardware partition we would
just end up with multiple BLK devices, like we do with SCSI LUNs at
present, which seems like it should work (with some code tweaks).

>
> Software partitioning (MBR, GPT, ...) is independent of the harboring
> block device.
>
> We already have a set of drivers for software partition tables in disk/.
> Currently the available methods of the drivers are defined in
> U_BOOT_PART_TYPE referring to struct part_driver.
>
> Currently struct part_driver knows only the following methods:
>
> - get_info()
> - print()
> - test()
>
> These drivers should be ome a uclass.
>
> gpt.c and mbr.c allow to create and delete partitions. I think we should add
>
> - create_partition()
> - delete_partition()
>
> to the uclass methods.

That sounds good to me, although since it is a partition uclass, we
can just use create() and delete().
>
> The partitions handled by cmd/mtdparts.c, cmd/nand.c are also software
> partitions. The difference to MBR, GPT is that the partition table is
> held in memory and not on disk. These partitions could be modeled in the
> same uclass.

For future work!

Regards,
SImon

> >>>
> >>>>>>
> >>>>>> It is compatible with what we have now and we could enable/disable the
> >>>>>> extra devices with a Kconfig.
> >>>>>>
> >>>>>> Regards,
> >>>>>> Simon
> >>>>>>
> >>>>>>
> >>>>>>
> >>>>>>>>
> >>>>>>>>> UCLASS_PARTITION_TABLE would be for the drivers in disk/.
> >>>>>>>>> UCLASS_FS would be for the drivers in fs/.
> >>>>>>>>> UCLASS_BLK will be for any objects exposing raw block IO. A software
> >>>>>>>>> partition does the same. It is created by the partition table driver as
> >>>>>>>>> child of the partition table udevice.
> >>>>>>>>>
> >>>>>>>>> In this model an eMMC device will not be a UCLASS_BLK device because it
> >>>>>>>>> does not expose block IO. It is the hardware partition that exposes this
> >>>>>>>>> interface.
> >>>>>>>>>
> >>>>>>>>> The suggested model will allow a clean description of nested partition
> >>>>>>>>> tables.
> >>>>>>>>>
> >>>>>>>>> In the UEFI world the software partition and its file system must be
> >>>>>>>>> mapped to a single handle with device path node type HD(). For the
> >>>>>>>>> parent block device we may create a child handle with partition number 0
> >>>>>>>>> (HD(0)). For the partition table we will not create a handle.
> >>>>>>>>>
> >>>>>>>>> Best regards
> >>>>>>>>>
> >>>>>>>>> Heinrich