On Mon, 6 Feb 2012, Johan Hovold wrote:
> Add macro which prints an error message only once if port is used a
> console.
>
> Reporting errors in a write path when port is used as a console could
> otherwise result in an infinite loop.
>
> Signed-off-by: Johan Hovold <jhovold@xxxxxxxxx>
> ---
> include/linux/usb/serial.h | 15 +++++++++++++++
> 1 files changed, 15 insertions(+), 0 deletions(-)
>
> diff --git a/include/linux/usb/serial.h b/include/linux/usb/serial.h
> index 4267a9c..7094f93 100644
> --- a/include/linux/usb/serial.h
> +++ b/include/linux/usb/serial.h
> @@ -389,5 +389,20 @@ do { \
> printk(KERN_DEBUG "%s: " format "\n", __FILE__, ##arg); \
> } while (0)
>
> +/*
> + * Macro for reporting errors in write path to avoid inifinite loop
> + * when port is used as a console.
> + */
> +#define dev_err_console(usport, fmt, ...) \
> +{ \
> + static bool __print_once; \
> + struct usb_serial_port *port = (usport); \
> + \
> + if (!port->port.console || !__print_once) { \
> + __print_once = true; \
> + dev_err(&port->dev, fmt, ##__VA_ARGS__); \
> + } \
> +}
Macro bodies like this are customarily wrapped in "do ... while (0)".
Otherwise a call such as
dev_err_console(...);
parses as two statements, not one, because of the final ';'. Although
this doesn't matter the way you have used dev_err_console, it could
cause problems in the future if somebody tries to write:
if (...)
dev_err_console(...);
else
...
Alan Stern
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