[RFC 07/22] dm: blk: add UCLASS_PARTITION
Simon Glass
sjg at chromium.org
Fri Nov 5 17:12:16 CET 2021
Hi Takahiro,
On Thu, 4 Nov 2021 at 20:49, AKASHI Takahiro <takahiro.akashi at linaro.org> wrote:
>
> On Thu, Nov 04, 2021 at 08:02:05PM -0600, Simon Glass wrote:
> > Hi,
> >
> > On Tue, 2 Nov 2021 at 01:43, Heinrich Schuchardt <xypron.glpk at 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 at 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 at 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 at chromium.org>:
> > > >>>>>> Hi,
> > > >>>>>>
> > > >>>>>> On Fri, 29 Oct 2021 at 13:26, Heinrich Schuchardt <xypron.glpk at gmx.de> wrote:
> > > >>>>>>>
> > > >>>>>>>
> > > >>>>>>>
> > > >>>>>>> Am 29. Oktober 2021 08:15:56 MESZ schrieb AKASHI Takahiro <takahiro.akashi at 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().
>
> I don't know why we need a "partition table" device in the middle
> of DM hierarchy.
> I believe that it simply makes the view of DM tree complicated
> without any explicit benefit.
Well we clearly have an API here. The partition uclass can:
- hold the partition table in dev_get_uclass_priv()
- support a read() operation to read the partition
- support create() to rewrite the partition table
- support delete() to overwrite/erase the partition table
Then it means that filesystems have the partition table as a parent
(unless they are whole-device filesystems), which makes sense
So that's why I like the idea.
Other than the extra complexity, is there anything else wrong with it?
Regards,
Simon
>
> -Takahiro Akashi
>
>
> > >
> > > 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
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