[Devel] Re: [PATCH 3/6] c/r: [pty 2/2] support for pseudo terminals

[Louis Rilling]

On 04/09/09 10:20 -0400, Oren Laadan wrote:
> This patch adds support for checkpoint and restart of pseudo terminals
> (PTYs). Since PTYs are shared (pointed to by file, and signal), they
> are managed via objhash.
> 
> PTYs are master/slave pairs; The code arranges for the master to
> always be checkpointed first, followed by the slave. This is important
> since during restart both ends are created when restoring the master.
> 
> In this patch only UNIX98 style PTYs are supported.
> 
> Currently only PTYs that are referenced by open files are handled.
> Thus PTYs checkpoint starts with a file in tty_file_checkpoint(). It
> will first checkpoint the master and slave PTYs via tty_checkpoint(),
> and then complete the saving of the file descriptor. This means that
> in the image file, the order of objects is: master-tty, slave-tty,
> file-desc.
> 
> During restart, to restore the master side, we open the /dev/ptmx
> device and get a file handle. But at this point we don't know the
> designated objref for this file, because the file is due later on in
> the image stream. On the other hand, we can't just fput() the file
> because it will close the PTY too.
> 
> Instead, when we checkpoint the master PTY, we _reserve_ an objref
> for the file (which won't be further used in checkpoint). Then at
> restart, use it to insert the file to objhash.
> 
> TODO:
> 
> * Better sanitize input from checkpoint image on restore
> * Check the locking when saving/restoring tty_struct state
> * Echo position/buffer isn't saved (is it needed ?)
> * Handle multiple devpts mounts (namespaces)
> * Paths of ptmx and slaves are hard coded (/dev/ptmx, /dev/pts/...)
> 
> Changelog[v1]:
>   - Adjust include/asm/checkpoint_hdr.h for s390 architecture
>   - Add NCC to kernel constants header (ckpt_hdr_const)
>   - [Serge Hallyn] fix calculation of canon_datalen
> 
> Signed-off-by: Oren Laadan <orenl at cs.columbia.edu>

[...]

> diff --git a/drivers/char/tty_io.c b/drivers/char/tty_io.c
> index a3afa0c..b8f8d79 100644
> --- a/drivers/char/tty_io.c
> +++ b/drivers/char/tty_io.c
> @@ -570,7 +582,9 @@ static void do_tty_hangup(struct work_struct *work)
>  	set_bit(TTY_HUPPED, &tty->flags);
>  	spin_unlock_irqrestore(&tty->ctrl_lock, flags);
>  
> -	/* Account for the p->signal references we killed */
> +	/* Account
> +
> +	   for the p->signal references we killed */
>  	while (refs--)
>  		tty_kref_put(tty);
>  

Nit: this hunk is certainly not needed ;)

[...]

Thanks,

Louis

-- 
Dr Louis Rilling			Kerlabs
Skype: louis.rilling			Batiment Germanium
Phone: (+33|0) 6 80 89 08 23		80 avenue des Buttes de Coesmes
http://www.kerlabs.com/			35700 Rennes
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