Hi Tobias,
On Tue, 7 Feb 2023 at 01:31, Tobias Waldekranz tobias@waldekranz.com wrote:
On mån, feb 06, 2023 at 21:02, Simon Glass sjg@chromium.org wrote:
Hi Tobias,
On Mon, 6 Feb 2023 at 01:30, Tobias Waldekranz tobias@waldekranz.com wrote:
On fre, feb 03, 2023 at 17:20, Simon Glass sjg@chromium.org wrote:
Hi Tobias,
On Fri, 3 Feb 2023 at 02:38, Tobias Waldekranz tobias@waldekranz.com wrote:
On ons, feb 01, 2023 at 13:20, Simon Glass sjg@chromium.org wrote:
Hi Tobias,
Hi Simon,
Thanks for the review!
On Wed, 1 Feb 2023 at 11:10, Tobias Waldekranz tobias@waldekranz.com wrote: > > blkmaps are loosely modeled on Linux's device mapper subsystem. The > basic idea is that you can create virtual block devices whose blocks > can be backed by a plethora of sources that are user configurable. > > This change just adds the basic infrastructure for creating and > removing blkmap devices. Subsequent changes will extend this to add > support for actual mappings. > > Signed-off-by: Tobias Waldekranz tobias@waldekranz.com > --- > MAINTAINERS | 6 + > disk/part.c | 1 + > drivers/block/Kconfig | 18 ++ > drivers/block/Makefile | 1 + > drivers/block/blk-uclass.c | 1 + > drivers/block/blkmap.c | 275 +++++++++++++++++++++++++++++++ > include/blkmap.h | 15 ++ > include/dm/uclass-id.h | 1 + > include/efi_loader.h | 4 + > lib/efi_loader/efi_device_path.c | 30 ++++ > 10 files changed, 352 insertions(+) > create mode 100644 drivers/block/blkmap.c > create mode 100644 include/blkmap.h >
[..]
This needs to be created as part of DM. See how host_create_device() works. It attaches something to the uclass and then creates child devices from there. It also operations (struct host_ops) but you don't need to do that.
Note that the host commands support either an label or a devnum, which I think is useful, so you might copy that?
I took a look at the hostfs implementation. I agree that labels are much nicer than bare integers. However, for block maps the idea is to fit in to the existing filesystem infrastructure. Addressing block devices using the "<interface> <dev>[:<part>]" pattern seems very well established...
You can still do that, so long as the labels are "0" and "1", etc. But it lets us move to a more flexible system in future.
> +{ > + static struct udevice *dev; > + int err; > + > + if (dev) > + return dev; > + > + err = device_bind_driver(dm_root(), "blkmap_root", "blkmap", &dev); > + if (err) > + return NULL; > + > + err = device_probe(dev); > + if (err) { > + device_unbind(dev); > + return NULL; > + }
Should not be needed as probing children will cause this to be probed.
So this function just becomes
uclass_first_device(UCLASS_BLKDEV, &
> + > + return dev; > +} > + > +int blkmap_create(int devnum)
Again, please drop the use of devnum and use devices. Here you could use a label, perhaps?
...which is why I don't think a label is going to fly here. Let's say I create a new ramdisk with a label instead, e.g.:
blkmap create rd blkmap map rd 0 0x100 mem ${loadaddr}How do I know which <dev> to supply to, e.g.:
ls blkmap <dev> /bootIt seems like labels are a hostfs-specific feature, or am I missing something?
We have the same problem with hostfs, since we have not implemented labels in block devices. For now you must use integer labels. But we will get there.
But there is no connection to the devnum that is allocated internally by U-Boot. Here's an experiment I just ran:
I created two squashfs images containing a single directory:
zero.squashfs: i_am_zero one.squashfs: i_am_oneThen I added a binding to them:
=> host bind 1 one.squashfs => host bind 0 zero.squashfsWhen accessing them, we see that the existing filesystem utilities work on the internally generated devnums, ignoring the labels:
=> ls host 1 i_am_zero/ 0 file(s), 1 dir(s) => ls host 0 i_am_one/ 0 file(s), 1 dir(s) =>Doesn't it therefore make more sense to stick with the established abstraction?
It is pretty clear that this is a bit silly though :-)
As in "this specific example will never be used in practice"? Sure :)
My point was just that the approach to stick to integer labels is brittle, since there is no connection between the label and the devnum used by existing commands.
Here's an even simpler example that might actually trip up a user:
=> host bind 1 one.squashfs => ls host 1 ** Bad device specification host 1 ** Couldn't find partition host 1 => ls host 0 i_am_one/ 0 file(s), 1 dir(s) =>
Yes, I get it. Perhaps this will spur us to look at device naming...one of the impediments has been that we don't use CONFIG_BLK in SPL on quite a few boards, so there are effectively two implementations, one of which does not use driver model. So naming doesn't exist in that case. It is hard to require driver model in SPL, but perhaps at some point we can require it if block devices are needed.
I mean, right now, it would be easier to stick with numbered devices. But we want to be able to support named devices (e.g. using struct udevice->name). A good way to be forward compatible is to support a label today.
When we do get to it, the less code that has piled up and needs converting, the more likely it is to happen.
I completely understand, and agree with, the direction you want to take this.
Sure, you have the problem as above, but mostly people are only going to use one of them, so it doesn't matter.
We could also have a way of obtaining a number from a label, if you want to go that far. But I suggest just telling people to use labels like "1" and "0" which should work.
Alright, well, if that is acceptable then I'll do it that way. For my own piece of mind, I think I'll also add some way of safely doing the reverse mapping for any label. Does the following look ok?
blkmap get <label> dev <var>This way you could extend it with other attributes in the future (e.g. size).
Yes that sounds great. Perhaps we can (at some point) extend that sort of thing to block devices in general.
Regards, SImon