Re: [PATCH] to select.c (and an apology)

From: almesber@lrc.di.epfl.ch
Date: Mon Jan 31 2000 - 02:40:11 EST

willy@thepuffingroup.com wrote:
> On Mon, Jan 31, 2000 at 03:56:03AM +0100, Patrick Mau wrote:
>> +/*
>> fds = (struct pollfd **)kmalloc(
>> (1 + (nfds - 1) / POLLFD_PER_PAGE) * sizeof(struct pollfd *),
>> GFP_KERNEL);

> (nfds * sizeof(void *) + POLLFD_PER_PAGE - 1) / POLLFD_PER_PAGE

Assuming that a struct pollfd * points to a page of pollfds, and fds is
an array of pointers, this is still wrong, e.g. assume nfds = 1,
sizeof(void *) = 4, POLLFD_PER_PAGE any value >= 2.

The original version yields a correct result and even seems a bit clearer,
unless nfds-1 becomes unsigned. In that case, something like

(nfds+POLLFD_PER_PAGE-1)/POLLFD_PER_PAGE*sizeof(struct pollfd *)

should help.

- Werner 

-- 
  _________________________________________________________________________
 / Werner Almesberger, ICA, EPFL, CH       werner.almesberger@ica.epfl.ch /
/_IN_N_032__Tel_+41_21_693_6621__Fax_+41_21_693_6610_____________________/

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