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 ;)
Thanks,
/mjt
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