Messages in this thread | | | Date | Wed, 10 Jun 2009 12:17:35 -0400 (EDT) | From | Steven Rostedt <> | Subject | Re: [PATCH 00/11] [GIT PULL] more updates for the tag format |
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On Wed, 10 Jun 2009, Theodore Tso wrote:
> On Wed, Jun 10, 2009 at 09:49:29AM -0400, Steven Rostedt wrote: > > > > > > Maybe I'm missing something, but looks like the this new format, while > > > simpler and easier to read, doesn't have support for using a more > > > complicated C expression as a printk argument. For example: > > > > > > TP_printk("dev %s ino %lu mode %d uid %u gid %u blocks %llu", > > > jbd2_dev_to_name(__entry->dev), __entry->ino, __entry->mode, > > > __entry->uid, __entry->gid, __entry->blocks) > > > > > > How should I handle the "jbd2_dev_to_name(__entry->dev)" argument to > > > TP_printk? The whole point of calling jbd2_dev_to_name() at TP_printk > > > time is to not bloat the ring buffer with a 32 byte devname. > > > > Understood, and the example you just gave also has the flaw that a > > userspace tool could not parse it, because it would not know what to do > > with "jbd2_dev_to_name()". > > > > This is why I suggested keeping the TP_printk, for cases like this. Since > > it is also currently useless in userspace. > > > > But we really should convert all cases, and I was toying with an idea to > > dynamically make your own data type, and be able to make a way to print > > it. > > Yes, another approach for handling this case would be to take my > "jbd2_dev_to_name" function and support it as a first-class tagged > type; after all, I'm sure ext4 won't be the only place that would like > to take a dev_t and print the device name. So this could certainly be > fixed by adding some kind of "<dev:xxx>" sort of tagged name.
Yep that could be done as long as we know the mapping will never change. Userspace needs know what those numbers mean.
> > But I think it would be good to keep TP_printk because otherwise I'll > have to scramble and change my marker->tracepoint patches during the > merge window, which would invalidate all of the testing to date.
Understood, I made it that both TP_printk and TP_FORMAT can exist together, but Christoph Hellwig doesn't like that idea. I'm thinking for quick debug sessions, TP_printk() be used. In fact, if we go to TP_FORMAT, I'll just make TP_printk no longer show up in the user format.
Then TP_printk() can be used for quick hacks, but if you want something merged, it would need to be added to the tag format.
> > I agree that the new tagged format is superior, but I'm wondering > whether it really makes sense to try to scramble and try to switch my > ext4/jbd2 users in the 36 hours or so before Linus opens the merge > window....
Relax, we already decided this is .32 material ;-)
-- Steve
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