Date: Wed, 16 Jan 2013 13:42:48 -0500 From: John Baldwin <jhb@freebsd.org> To: Alfred Perlstein <bright@mu.org> Cc: svn-src-projects@freebsd.org, Alfred Perlstein <alfred@freebsd.org>, src-committers@freebsd.org Subject: Re: svn commit: r245259 - projects/utrace2 Message-ID: <201301161342.49065.jhb@freebsd.org> In-Reply-To: <50F5D935.2010309@mu.org> References: <201301101758.r0AHw6m7078896@svn.freebsd.org> <201301151443.25121.jhb@freebsd.org> <50F5D935.2010309@mu.org>
next in thread | previous in thread | raw e-mail | index | archive | help
On Tuesday, January 15, 2013 5:33:25 pm Alfred Perlstein wrote: > On 1/15/13 11:43 AM, John Baldwin wrote: > > On Monday, January 14, 2013 4:35:07 pm Alfred Perlstein wrote: > >> On 1/14/13 3:32 PM, John Baldwin wrote: > >>> On Monday, January 14, 2013 2:58:23 pm Alfred Perlstein wrote: > >>>> On 1/14/13 2:01 PM, John Baldwin wrote: > >>>>> On Monday, January 14, 2013 1:44:28 pm Alfred Perlstein wrote: > >>>>>> I think we are basically in agreement, however we differ on the following two points, whereas now I think we only differ on a single point. > >>>>>> > >>>>>> 1) belief that a 4 character string signature is superior to a protocol/version tuple. > >>>>>> > >>>>>> After looking at the code and thinking about this quite a bit, I agree with you that string based namespace is nicer, however I think we > >>> need the > >>>>> following changes: > >>>>>> a) define the system namespace to have "_" preceding the trace name. so RTLD -> _RTL > >>>>>> b) or maybe we need another few characters? 6 or 8 so that it can still be nice. so "_RTL" -> "_RTLD\0\0\0", "_MALLOC\0" > >>>>>> c) we add a version field after the character string. > >>>>>> d) we create a mechanism for requesting a utrace allocation namespace somewhere (/usr/share/utrace/allocations.txt) where vendors can > >>> allocate > >>>>> strings. > >>>>>> 2) you believe that filtering this all through utrace(2) is OK. I would prefer that we leave utrace(2) alone and move forward with > > utrace2(2) > >>> to > >>>>> leave behind all the unformatted data we used to have. I would like to leave utrace(2) in the system and add utrace2(2) for new consumers. > >>>>>> What do you think? > >>>>>> > >>>>>> My end goal is to make this something that more users can grab and use for a quick and handy debug tool and to actually build on this > > somewhat, > >>>>> (libutrace) what we have now (unstructured globs of whatever) does not work. > >>>>> > >>>>> I disagree with this last assertion. On what basis do you claim that what we > >>>>> have now does not work? Do you have any specific examples besides > >>>>> hypothetical cases? I fail to see how utrace() in its current form is not > >>>>> already useful, and I've yet to see a convincing argument from you that it is > >>>>> not. > >>>>> > >>>> #include <stdio.h> > >>>> #include <stdlib.h> > >>>> > >>>> int > >>>> main(void) > >>>> { > >>>> void *ptr = 0x52544c44; > >>>> > >>>> realloc(ptr, 200); > >>>> } > >>> That is fair, though you could easily fix that by changing malloc to use a > >>> signature going forward. :) That is a far simpler change than adding an > >>> entirely new system call. You also ignored the point that by making an API > >>> change you _are_ forcing all the current hypothetical utrace() users you are > >>> so worried about to make a code change. > >> Well, wouldn't the hypothetical users just continue to use the old code > >> until they are ready to move forward? Having both utrace and utrace2 > >> would not impact force anyone to move. > > Presumably if you really want to deprecate it you need to remove it from the > > header so it is truly hidden? (At least in 11 if not in 10?) > > I don't really want to deprecate it. I just want to provide a new > subsystem that's more regular. > > I only offered to deprecate it because I thought you were hinting at that. > > I'd rather keep both old and new. I do NOT want to break people. Ok. I can't think of a better name than utrace2() in that case. I still think -u should enable both utrace() variants for ktrace and kdump. It would be nice if you were to support a 4 char signature of some sort and have kdump display that instead of 'USER', so you get: <pid> RTLD dl_open(...) vs the current: <pid> USER RTLD: dl_open(...) and so that you can specify that 4 char for a filter list somehow (maybe -U accepts a comma-separated list of signatures for "user events"?). If you want to keep integers instead of encoding the signature in the tag values then you could use a table for the system-assigned tags to map them to a signature. OTOH, if we just encode the signature as the tag then kdump would automatically support "new" tags (including user-assigned tags) for purposes of filtering, etc. -- John Baldwin
Want to link to this message? Use this URL: <https://mail-archive.FreeBSD.org/cgi/mid.cgi?201301161342.49065.jhb>