Hello Sam,
many thnkas for your patchset!
On 12.08.23 02:06, Sam Edwards wrote:
Hi UBI maintainers,
My target's rootfs is a read-only filesystem stored in a static UBI volume, mounted via a "ubiblock" device after boot. I'd also like to keep the boot files in the same filesystem, so that it's all coupled together. To that end, I'm working on a patchset so that U-Boot can read static UBI volumes as read-only block devices (paralleling Linux's ubiblock mechanism).
I'm very happy with how the first 3 patches in this series turned out (so I'm not asking about them per se, though feedback is certainly welcome). The fourth is where I got stuck: while the code definitely works, it requires bringing DM headers into disk/part.c, which certainly will not fly in mainline. I need to plumb this through drivers/block/blk-uclass.c to do it "properly."
Part of the problem here is that these are *volumes,* but they are (optionally) *named.* In U-Boot's current view of block devices, it is only a partition, and not a volume, that may have a name. These aren't "partitions" in U-Boot's view, since a partition is a contiguous slice of a bigger block device, while these are (logically) separate block devices.
So, I would need to invent a new function that can look up a named (sub)volume. I also probably need to invent new syntax, so that I'm not overloading the 0:1 syntax for partitions. I'm not especially beholden to the ':', but I do want to use the same syntax for volume numbers and volume names, to mirror Linux's `ubi.block=x,y` syntax.
I'm also trying to reclaim the name "ubi" to refer to a UBI volume, while U-Boot currently thinks it should refer to the presently-mounted UBIFS. In my current series, the meaning of "ubi" depends on whether ubifs is mounted, for backwards-compatibility. If this isn't palpable, I could consider other options like "ubivol"/"ubiblock"/"ubiblk"/"ubistatic"/...
So, the feedback I'm hoping for would be:
- What is a good syntax for referring to a logical volume by name or ID? Keeping in mind this may affect more than just UBI, if e.g. U-Boot learns to peer inside LVM2s in the future.
Yes, we should have here some generic part...
- What should I call the block functions for looking up a block device's subvolume by type+parentidx+{name,ID}?
- Is my strategy of reclaiming "ubi" sound, or should I be conceding that to UBIFS and using a new type name for static UBI volumes?
- Does my choose_blksz_for_volume() function make sense, or should I always be using a preferred block size (like 512) if possible?
Your patches look good to me, and yes, we have to discuss changes in disk/part.c
I added Simon here as he has much more knowledge here, hope he can comment this part.
bye, Heiko
Cheers, Sam
Sam Edwards (4): mtd: ubi: register UBI attachments as DM devices mtd: ubi: bind block device driver for static volumes disk: part: fall-through if "ubi" requested but ubifs not mounted HACK: enable access to `ubi 0:volname` block devices
cmd/ubi.c | 11 +++ disk/part.c | 70 +++++++++++-- drivers/mtd/ubi/Makefile | 1 + drivers/mtd/ubi/ubi-uclass.c | 184 +++++++++++++++++++++++++++++++++++ include/dm/uclass-id.h | 1 + include/ubi_uboot.h | 5 + 6 files changed, 264 insertions(+), 8 deletions(-) create mode 100644 drivers/mtd/ubi/ubi-uclass.c