On Wed, 16 Jan 2013 20:07:49 +0000 (UTC) Grant Edwards <grant.b.edwards@xxxxxxxxx> wrote: > Are calls to a tty driver's open()/close() methods serialized by the > tty layer? If so, has this always been the case? They are not fully serialized - never have been. A lot of the drivers were always racy, some that have not been fully converted to the port helpers still are. > >From looking at example tty drivers in the 3.7.2 source tree, it > appears that they assume calls to open()/close() are serialized. > > The old driver I'm working on had its own internal locking to protect > race conditiions when incrementing and decrementing of a port's open > count. That counter is being prelaced by tty->port->count, and in > existing in-kernel tty drivers it doesn't look like there is any > locking when that count is incremented during an open(). Use the tty_port helpers. They will also handle all the other detail you need. The helpers themselves provide serialized activate/shutdown callbacks on the port which are serialized against each other and hangups. The port helpers will also ensure your refcounting is right, you don't have open/close/hangup races and that you get the required POSIX semantics. The port helpers are designed so you can propogate your own error codes either by wrapping them or by returning your own error code from port->activate() which will be duly propogated to user space. Alan -- To unsubscribe from this list: send the line "unsubscribe linux-serial" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
