On Fri, Nov 26, 2010 at 13:11, Tvrtko Ursulin <tvrtko.ursulin@xxxxxxxxxx> wrote: > On Monday 22 Nov 2010 00:37:21 Alexey Zaytsev wrote: >> +struct fanotify_opt_hdr { >> + Â Â Â __u8 type; >> + Â Â Â __u8 reserved; >> + Â Â Â __u16 len; >> + Â Â Â /* Payload goes here. */ >> +}; >> + >> +#define FANOTIFY_METADATA_VERSION Â Â Â3 >> >> Âstruct fanotify_event_metadata { >> - Â Â Â __u16 event_len; >> + Â Â Â __u16 event_len; /* Including the options */ >> Â Â Â Â __u8 vers; >> - Â Â Â __u8 reserved; >> + Â Â Â __u8 options_offset; /* Aka header length */ >> Â Â Â Â __s32 fd; >> Â Â Â Â __aligned_u64 mask; >> Â Â Â Â __s32 pid; >> + Â Â Â /* Options go here. */ >> Â}; > > I am not 100% comfortable with having 16 bits length fields because I am just > not sure there is a measurable performance difference versus just going with > 32 bits. I'm not concerned so much with the performance, as with the storage. If we are generating events for every access on a mount point, some consumers might build a considerable backlog over a period of high activity. Would be good if we could cut the event size by 1/3 for free. And I don't see an event growing 64k even with the options. Do you? > > Also, options_offset is, if I understood it correctly, basically the lenght of > fanotify_event_metadata. As such, isn't that field redundant since the lenght > is implied from the protocol version? There are two problems there. 1) You lose backwards-compatibility. It's still an ABI breakage, even if you tell the users about it. 2) You can't build a program to account for different fanotify versions: if (vers >= N) { use the cool stuff } else if {vers >= N-1} { still good } -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html