On Mon, 2012-04-30 at 10:43 +0400, Michael Tokarev wrote:
> On 30.04.2012 10:27, Michael Tokarev wrote:
> >> On 04/29/2012 01:54 PM, Linux Kernel Mailing List wrote:
> >>> However, a prettier solution exists now thanks to the packetized pipe
> >>> mode. By marking the communication pipe as being packetized (by simply
> >>> setting the O_DIRECT flag), we can always just write the bigger packet
> >>> size, and if user-space does a smaller read, it will just get that
> >>> partial end result and the extra alignment padding will simply be thrown
> >>> away.
> >
> >> +static inline int autofs_prepare_pipe(struct file *pipe)
> >> +{
> >> + if (!pipe->f_op || !pipe->f_op->write)
> >> + return -EINVAL;
> >> + if (!S_ISFIFO(pipe->f_dentry->d_inode->i_mode))
> >> + return -EINVAL;
> >> + /* We want a packet pipe */
> >> + pipe->f_flags |= O_DIRECT;
> >> + return 0;
> >> +}
> >> +
> >
> > @@ -376,7 +376,7 @@ static int autofs_dev_ioctl_setpipefd(st
> > err = -EBADF;
> > goto out;
> > }
> > - if (!pipe->f_op || !pipe->f_op->write) {
> > + if (autofs_prepare_pipe(pipe) < 0) {
> > err = -EPIPE;
> > fput(pipe);
> > goto out;
> >
> > I've one more concern. I'm not sure but I think there's some
> > risk still. This packetizing gets applied to all VERSIONS of
> > the autofs PROTOCOL. Which means it will be applied to the
> > lowest supported version (3) TOO, but did that version read
> > whole packets too?
>
> I think this is a false alarm. I checked autofs v3 and v4
> userspace code (found on http://www.kernel.org/pub/linux/daemons/autofs )
> and they both read whole packet at once, not piece-wise.
>
> I didn't test if any of these actually work with any current
> kernel, however ;)
Yep, all the autofs releases use a sizeof() the relevant structure when
reading the kernel pipe, so that should be ok.
Ian
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