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SubjectRe: [PATCH 6/6] vfs: introduce FMODE_NEG_OFFSET for allowing negative f_pos
On Sat, 16 Jan 2010 21:54:39 +0900
OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> wrote:

> Wu Fengguang <fengguang.wu@intel.com> 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.

Thanks,
-Kame



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