From 1be491fca12ff599c37ceaf7e9042ebee9f0068e Mon Sep 17 00:00:00 2001 From: Johannes Berg Date: Sun, 5 Jul 2009 14:51:06 +0200 Subject: rfkill: prep for rfkill API changes We've designed the /dev/rfkill API in a way that we can increase the event struct by adding members at the end, should it become necessary. To validate the events, userspace and the kernel need to have the proper event size to check for -- when reading from the other end they need to verify that it's at least version 1 of the event API, with the current struct size, so define a constant for that and make the code a little more 'future proof'. Not that I expect that we'll have to change the event size any time soon, but it's better to write the code in a way that lends itself to extending. Due to the current size of the event struct, the code is currently equivalent, but should the event struct ever need to be increased the new code might not need changing. Signed-off-by: Johannes Berg Signed-off-by: John W. Linville --- include/linux/rfkill.h | 14 ++++++++++++++ 1 file changed, 14 insertions(+) (limited to 'include/linux') diff --git a/include/linux/rfkill.h b/include/linux/rfkill.h index 2ce29831feb..f3d5812693d 100644 --- a/include/linux/rfkill.h +++ b/include/linux/rfkill.h @@ -82,6 +82,20 @@ struct rfkill_event { __u8 soft, hard; } __packed; +/* + * We are planning to be backward and forward compatible with changes + * to the event struct, by adding new, optional, members at the end. + * When reading an event (whether the kernel from userspace or vice + * versa) we need to accept anything that's at least as large as the + * version 1 event size, but might be able to accept other sizes in + * the future. + * + * One exception is the kernel -- we already have two event sizes in + * that we've made the 'hard' member optional since our only option + * is to ignore it anyway. + */ +#define RFKILL_EVENT_SIZE_V1 8 + /* ioctl for turning off rfkill-input (if present) */ #define RFKILL_IOC_MAGIC 'R' #define RFKILL_IOC_NOINPUT 1 -- cgit v1.2.3