- B_TRIM_DEVICE on a ram disk frees all requested pages. Reading from a
trimmed page returns all 0s. This can be used with fstrim to release
memory for the parts not used by the filesystem, without unregistering
then registering the device.
- Add icon and ioctl to get it.
- Add it to the image, because it works reasonably well and there is no
reason not to include it.
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