Messages in this thread | | | From | Tom Zanussi <> | Date | Mon, 18 Jul 2005 09:41:29 -0500 | Subject | Re: Merging relayfs? |
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Steven Rostedt writes: > On Sun, 2005-07-17 at 10:52 -0500, Tom Zanussi wrote: > > > > > > > > > - overwrite mode can be implemented via the buffer switch callback > > > > > > > > The buffer switch callback is already where this is handled, unless > > > > you're thinking of something else - one of the first checks in the > > > > buffer switch is relay_buf_full(), which always returns 0 if the > > > > buffer is in overwrite mode. > > > > > > I mean, relayfs doesn't has to know about this, the client itself can do > > > it (e.g. via helper functions). > > > > In a previous version, we did something like having the client pass > > back a return value from the callback indicating whether or not to > > continue or stop. I can try doing something like that instead again. > > Tom, > > I'm actually very much against this. Looking at a point of view from the > logdev device. Having a callback to know to continue at every buffer > switch would just be slowing down something that is expected to be very > fast. I don't see the problem with having an overwrite mode or not. Why > can't relayfs know this? It _is_ an operation of relayfs, and having it > pushed to the client would seem to make the client need to know more > about how relayfs works that it needs to. Because, the logdev device > doesn't care about buffer switches.
I don't think it would slow anything down - it would be pretty much the same code being executed as before e.g. the buffer_start() callback for overwrite mode could look like this:
int buffer_start() { ... return 1; // continue unconditionally }
And for no-overwrite mode:
int buffer_start() { ... return !relay_buf_full(buf); // continue if not full }
Since the buffer start callback already returns the amount that's supposed to be reserved at the start of the sub-buffer, I'd have to make that an outparam instead, I guess, but it's basically the same code handling the overwrite/no-overwrite condition.
Tom
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