1************************************************************************** 2* The following are notes for any script that uses the "fbt" provider. 3* To identify these scripts, check the "STABILITY" section of the script's 4* man page, or try grepping for "fbt" on the script. 5* 6* $Id: ALLfbt_notes.txt,v 1.1.1.1 2015/09/30 22:01:08 christos Exp $ 7* 8* COPYRIGHT: Copyright (c) 2007 Brendan Gregg. 9************************************************************************** 10 11 12What is the "fbt" provider?... 13 14* A DTrace library of probes that instruments raw kernel function calls. 15* An "unstable" provider; meaning, scripts written using "fbt" are not 16 guarenteed to work on future versions of the OS - including after 17 patching the kernel. 18 19In a perfect world... 20 21* None of the DTraceToolkit scripts would use the "fbt" provider; instead 22 they would all use stable providers such as "proc", "sched", "io", etc. 23* All the DTraceToolkit scripts would run on any system that supports DTrace. 24 25In the real world... 26 27* Not all stable providers exist yet. Many are in development, such as 28 stable networking providers. 29* In the meantime, useful tools such as "tcpsnoop" and "tcptop" can 30 only be written using the unstable "fbt" provider (and these scripts have 31 broken several times due to kernel changes since they were first written). 32* "fbt" provider based scripts, 33 - only run on a particular OS (eg, Solaris) 34 - may only run on a particular version of an OS (eg, Solaris 10 3/05) 35 - are likely to break for future OS releases (eg, Solaris 10 6/06) 36* "fbt" provider based scripts also make the impossible possible, albiet 37 in a very unstable way, as a temporary solution while stable providers 38 are still in development. 39* Once stable providers exist, "fbt" scripts can be rewritten to use them; 40 however these new scripts will only run on newer OS builds that support 41 the stable providers. (in other words, this won't help you if you remain 42 on Solaris 10 6/06; you'll need to upgrade, or survive with "fbt"). 43* Only some of the DTraceToolkit scripts use "fbt", and only a portion of 44 those have encountered stability issues - so this issue is limited. 45 46The "fbt" provider exports raw kernel implementation, which isn't guarenteed 47to be stable nor should it ever be (to do so would freeze kernel development 48and bug fixes). The only practical solution is the development and 49integration of stable providers (although that doesn't help people who keep 50running older versions of the OS). 51 52More harm than good?... 53 54Is the inclusion of these "fbt" scripts more harm than good? Consider, 55 56* the good, 57 - shows what is possible with DTrace 58 - should help a number of people solve specific performance issues, 59 on systems where they run 60 - a customer who really wants these scripts but on an OS version 61 where they don't work, have at least the source as a starting 62 point (and in some cases, the fix was trivial) 63 64* the bad, 65 - teases and frustrates people who find these scripts don't work 66 on their OS 67 68To minimise this issue, only a small number of "fbt" scripts have been 69included, and they have been documented (see their man page) as unstable. 70 71Can I help?... 72 73If you really like an "fbt" based script and would like to keep using it 74in a stable way, it may help to raise that with your vendor (Sun for Solaris, 75Apple for MacOS). Sun has OpenSolaris forums, such as dtrace-discuss, which 76are read by their engineers and the public. 77 78