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SubjectRe: [PATCH 4/4] TTY: call tty_driver_lookup_tty unconditionally
Ccing H.Peter Anvin.

Jiri Slaby [jirislaby@gmail.com] wrote:
| On 10/12/2011 11:32 AM, Jiri Slaby wrote:
| > Commit 4a2b5fddd5 (Move tty lookup/reopen to caller) made the call to
| > tty_driver_lookup_tty conditional in tty_open. It doesn't look like it
| > was an intention. Or if it was, it was not documented in the changelog
| > and the code now looks weird. For example there would be no need to
| > remember the tty driver and tty index. Further the condition depends
| > on a tty which we drop a reference of already.
| >
| > If I'm looking correctly, this should not matter thanks to the locking
| > currently done there. Thus, tty_driver->ttys[idx] cannot change under
| > our hands. But anyway, it makes sense to change that to the old
| > behaviour.
|
| Well, this doesn't work for ptys. devpts lookup code expects an inode to
| be one of devpts filesystem (/dev/pts/*), not something on tmpfs like
| /dev/tty. So it looks like the change was intentional, but very
| undocumented and leaving there some unused code.

Yes this was intentional - even though the tty_driver_lookup() was
unconditional in tty_init_dev() I believe it did not do anything useful
when called from ptmx_open(). ptmx_open() would be setting up a new pty and
the lookup would not find a tty.

Would the following change to tty_open() help ?

got_driver:
+ /* check if we are opening a new pty or reopening an existing tty */
if (!tty) {
- /* check whether we're reopening an existing tty */
tty = tty_driver_lookup_tty(driver, inode, index);

I am not sure about the unused code you refer to above. Can you please
clarify ?

Sukadev



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