When using the ls userspace program to list a specific device file,
nothing would be displayed. This was because ls only tests for T_FILE
and T_DIR. T_DEVICE files would fall through the case block.

Adding T_DEVICE to the T_FILE case allows a device file to be listed.

    $ ls console
    console        3 19 0

'kfree' has a parameter named 'pa' but referenced in the comment as 'v'.

When compiling with gcc version 12, this change also avoids the
compiler warning "infinite recursion detected" for runcmd()

This reverts commit 759bb341.

The legacy interface is confusing. It's better to make virtio_disk
conform to the virtio spec. This is supported in QEMU since 4.2 by
disabling force-legacy for virtio-mmio.

Matúš Jókay <matus.jokay@stuba.sk>)

The terminating NULL string is already included (see sys_exec()).

If va % PGSIZE == 0 and size == 0, we have last < a at the start of
the loop so we might never terminate.  That being said, this
particular case couldn't be triggered for now.