system call lecture a little clearer.

system call lecture a little clearer.

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 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.