lkml.org 
[lkml]   [2010]   [Jan]   [17]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
    /
    Date
    From
    SubjectRe: [PATCH 6/6] vfs: introduce FMODE_NEG_OFFSET for allowing negative f_pos
    On Mon, 18 Jan 2010 10:17:48 +0900
    OGAWA Hirofumi <hirofumi@mail.parknet.co.jp> wrote:

    > KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.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.
    >
    > 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



    \
     
     \ /
      Last update: 2010-01-18 02:31    [W:0.027 / U:90.452 seconds]
    ©2003-2016 Jasper Spaans. hosted at Digital OceanAdvertise on this site