Re: Merging relayfs?

[Tom Zanussi <zanussi@us.ibm.com>]

Karim Yaghmour writes:
 > 
 > Tom Zanussi wrote:
 > > - removed the deliver() callback
 > > - removed the relay_commit() function
 > 
 > This breaks LTT. Any reason why this needed to be removed? In the end,
 > the code will just end up being duplicated in ltt and all other users.
 > IOW, this is not some potential future use, but something that's
 > currently being used.

Because I realized that like the padding and commit arrays, they're
not really necessary.

In all the examples, the padding is saved in space reserved at the
beginning of the sub-buffer via subbuf_start_reserve(), except that
now the padding is passed into the subbuf_start() callback rather than
kept in an array.  The padding value passed in is then directly saved
in the reserved padding space.

Similarly, in the case of the reserve/commit example, extra space is
also reserved for the commit count using subbuf_start_reserve().
After space for an event is reserved using relay_reserve() and
completely written, the event length is added to that commit value.
In userspace, the sub-buffer reading loop looks at the commit value in
the sub-buffer, and if it matches (sub-buffer size - padding), the
buffer has been completely written and can be saved, otherwise it's
not yet complete and is checked again the next time around.  This way,
there's no need for a deliver() callback, the relay_commit() is
replaced with the increment of the reserved commit value, the arrays
aren't needed and you get the same result in the end in a much simpler
way, IMHO.

But if you see a problem with it or have any suggestions to make it
better/different, please let me know...

Tom


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