Messages in this thread | | | Subject | Re: [PATCH 4/4] fanotify: Expose the file changes to the user | From | Eric Paris <> | Date | Mon, 29 Nov 2010 13:14:33 -0500 |
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On Mon, 2010-11-29 at 19:51 +0300, Alexey Zaytsev wrote:
[rewriting history!] > struct fanotify_event_metadata { > __u32 event_len; /* Including the options */ > __u8 vers; > __u8 options_offset; /* Aka header length */ > __u16 reserved; > __aligned_u64 mask; > __s32 fd; > __s32 pid; > /* Options go here. */ > };
> and let's make both vers and options_offset u8, just in case we need the > other 2 bytes in the future:
So the last discussion is around vers and options_offset.
Alexy: Tvrtko: __u8 vers; __u16 vers; __u8 options_offset; __u16 options_offset; __u16 unused;
The only type of long option that first comes to mind is a filename. A filename could easily blow out the __u8 options_offset. I probably shouldn't put that in the event_metadata since it wouldn't be fixed length and it wouldn't allow fixed offset extention of the event_metadata, so maybe I shouldn't worry about it. I'm trying to think of reasons why __u8 isn't adequate other than my usual "just make it bigger than we ever need"
You'll notice I'm using __u64 for the mask, even though we don't come close to filling up an __u32 at this point.
Even though I can't think of a likely reason __u8 is bad I think I like the 'Tvrtko' option better. I think we should do a compromise:
Eric: __u8 vers; __u8 unused; __u16 options_offset;
If we ever overload vers we can expand into another field. Would could change unused into vers2 and define the version as vers + vers2; vers2 could even exist somewhere else in the metadata. That can be done once we get to version 254 while maintaining backwards compat beyond 255. If we ever overflow options_offset we are screwed since old userspace wouldn't know how to handle things.
So, if you want to send me a patch that implements the above (along with the obvious version bump to 3, I'll queue it up for this merge window even though we have an ABI compatible solution.
-Eric
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