On Mon, 18 Jan 2010 10:17:48 +0900
OGAWA Hirofumi <hirofumi@xxxxxxxxxxxxxxxxxx> wrote:
> KAMEZAWA Hiroyuki <kamezawa.hiroyu@xxxxxxxxxxxxxx> writes:
>
> >> > +static int
> >> > +__negative_fpos_check(struct file *file, loff_t pos, size_t count)
> >> > +{
> >> > + /*
> >> > + * pos or pos+count is negative here, check overflow.
> >> > + * too big "count" will be caught in rw_verify_area().
> >> > + */
> >> > + if ((pos < 0) && (pos + count < pos))
> >> > + return -EOVERFLOW;
> >> > + if (file->f_mode & FMODE_NEG_OFFSET)
> >> > + return 0;
> >> > + return -EINVAL;
> >> > +}
> >> > +
> >> > /*
> >> > * rw_verify_area doesn't like huge counts. We limit
> >> > * them to something that fits in "int" so that others
> >> > @@ -222,8 +236,11 @@ int rw_verify_area(int read_write, struc
> >> > if (unlikely((ssize_t) count < 0))
> >> > return retval;
> >> > pos = *ppos;
> >> > - if (unlikely((pos < 0) || (loff_t) (pos + count) < 0))
> >> > - return retval;
> >> > + if (unlikely((pos < 0) || (loff_t) (pos + count) < 0)) {
> >> > + retval = __negative_fpos_check(file, pos, count);
> >> > + if (retval)
> >> > + return retval;
> >> > + }
> >> >
> >> > if (unlikely(inode->i_flock && mandatory_lock(inode))) {
> >> > retval = locks_mandatory_area(
> >>
> >> Um... How do lseek() work? It sounds like to violate error code range.
> >
> > This is for read-write. As far as I know,
> > - generic_file_llseek,
> > - default_llseek
> > - no_llseek
> >
> > doesn't call this function.
>
> It seems to allow to set negative value to ->f_pos, right?
yes. Some file (/dev/kmem) requires that.
> So, lseek() returns (uses) it?
lseek can return negative value, as far as I know.
Thanks,
-Kame
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