Hello,
> > > Is it just me, or does
> > >
> > > ((user_addr + iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE -
> > > user_addr/PAGE_SIZE)
> > >
> > > not simplify to
> > >
> > > = ((iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE +
> > > user_addr/PAGE_SIZE - user_addr/PAGE_SIZE)
> > >
> > > = ((iov[seg].iov_len + PAGE_SIZE - 1)/PAGE_SIZE)
> > >
> > > = DIV_ROUND_UP(iov[seg].iov_len, PAGE_SIZE)
> > >
> > > CMIIW.
> >
> > I double-checked this and I believe you're correct. It's simpler to
> > see when you do:
> >
> > x = user_addr
> > y = iov[seg].iov_len
> > z = PAGE_SIZE
> >
> > So
> >
> > (x + y + z - 1)/z - x/z
> >
> > = [x + (y + z - 1)]/z - x/z
> >
> > = [xz + z(y + z - 1)]/z^2 - x/z
> >
> > = x/z + (y + z - 1)/z - x/z
> >
> > And the rest follows from your simplifications.
>
> It doesn't work:
>
> ((3+4+5-1)/5) - (3/5) = 2
> ((4+5-1)/5) = 1
Logic was wrong but conclusion was right :) and so was Nishanth:
(a + b) + c = a + (b + c)
and
k l k + l
- + - = -----
m m m
thus:
(user_addr + iov[seg].iov_len + PAGE_SIZE - 1) = user_addr + (iov[seg].iov_len
+ PAGE_SIZE - 1)
and
user_addr + iov[seg].iov_len + PAGE_SIZE - 1 user_addr
-------------------------------------------- - --------- =
PAGE_SIZE PAGE_SIZE
user_addr iov[seg].iov_len + PAGE_SIZE - 1 user_addr
--------- + -------------------------------- - --------- =
PAGE_SIZE PAGE_SIZE PAGE_SIZE
iov[seg].iov_len + PAGE_SIZE - 1
--------------------------------
PAGE_SIZE
or even more:
iov[seg].iov_len - 1
-------------------- + 1
PAGE_SIZE
Regards,
Mariusz
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