why UBI static volumes are flagged as DEVFS_IS_CHARACTER_DEV

[Sascha Hauer]

On Thu, Oct 06, 2016 at 10:17:27AM +0200, Teresa Remmet wrote:
> Hello Giorgio,
> 
> Am Mittwoch, den 05.10.2016, 15:23 +0200 schrieb iw3gtf at arcor.de:
> > Hi,
> > 
> > I noticed that the commit id c087e0804f0290e9886899e8a3cccb07c4ce088b flagged static
> > UBI volumes as DEVFS_IS_CHARACTER_DEV.
> > 
> > A consequence of this flag is that commands like:
> > 
> > # cp /dev/nand0.ubi_volumes.ubi.my_static_vol file
> > 
> > will not work because the cp command will see a src file (the static UBI volume) with a size
> > of -1 (FILE_SIZE_STREAM) and keep on reading from the volume until a flood of
> > "UBI assert failed in ubi_eba_read_leb at 359" asserts comes out of the console.
> > 
> > I tried to comment out the flag assignment, just to see what happen:
> > 
> > int ubi_volume_cdev_add(struct ubi_device *ubi, struct ubi_volume *vol)
> > {
> > ...
> > 	cdev->size = vol->used_bytes;
> > 
> > //	if (vol->vol_type == UBI_STATIC_VOLUME)
> > //		cdev->flags = DEVFS_IS_CHARACTER_DEV;
> > 
> > 	cdev->dev = &vol->dev;
> > ...
> > 
> > and then the cp command worked than as expected.
> > 
> > Could someone shortly confirm that the DEVFS_IS_CHARACTER_DEV flag for static UBI volumes
> > is really needed (to avoid some other problems that my superficial test does not triggers) ?
> 
> the size of a static ubi volume device is equal to the image size you
> flashed. When you create a new static ubi volume the size is 0, as it is
> empty.
> We need the chardev flag to be able to update the static ubi volume or
> barebox will complain that there is not enough space.

Then I think we need another solution for that. UBI volumes are clearly
not character devices, so we shouldn't set this flag to work around
other issues we have.

Currently devfs_truncate is implemented like:

static int devfs_truncate(struct device_d *dev, FILE *f, ulong size)
{
        if (f->fsdev->dev.num_resources < 1)
                return -ENOSPC;
        if (size > resource_size(&f->fsdev->dev.resource[0]))
                return -ENOSPC;
        return 0;
}

Maybe we need an optional cdev->ops->truncate() to let the UBI volumes be
able to overwrite this behaviour?

Sascha

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