Linus Torvalds writes: (Summary)
So we have
offset = pos - arg_end +1
(from the above initialization of offset), but we also know that
pos + count <= end_end
and since we've limited end_end to "arg_end + PAGE_SIZE -1" we have
pos + count <= arg_end + PAGE_SIZE -1
agreed? equation as
pos = arg_end + offset - 1
And the same time we can take that "pos + count" inequality, and
replacing "pos", we get
arg_end + offset - 1 + count <= arg_end + PAGE_SIZE -1
and then we can remove "arg_end - 1" from both sides, and get
offset+count <= PAGE_SIZE
agreed?
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