[lttng-dev] [PATCH lttng-modules 0/1] Introduce configure script to describe changes in linux kernel interface

[Roxana Nicolescu]

This script described the changes in the linux kernel interface that
affect compatibility with lttng-modules.

It is introduced for a specific usecase where commit
d87a7b4c77a9: "jbd2: use the correct print format"
broke the interface between the kernel and lttng-module. 3 variables
changed their type to tid_t (transaction, head and tid) in multiple
function declarations. The lttng module was updated properly to ensure
backwards compatibility by using the version of the kernel.
But this change took into account only long term supported versions.
As an example, ubuntu 5.19 kernels picked the linux kernel change from
5.15 without actually changing the linux kernel upstream version. This
means the current tooling does not allow to fix the module for newer
ubuntu 5.19 kernels.

This script is supposed to solve the problem mentioned above, but to
also make this change easier to integrate.
We check the linux kernel header (include/trace/events/jbd2.h) if the
types of tid, transaction and head variable have changed to tid_t and
define these 3 variables in 'include/generated/config.h':
TID_IS_TID_T 1
TRANSACTION_IS_TID_T 1
HEAD_IS_TID_T 1

In 'include/instrumentation/events/jbd2.h' we then check these to define
the proper type of transaction, head and tid variables that will be
later used in the function declarations that need them.

This change is meant to remove the dependency on linux kernel version
and the outcome is a bit cleaner that before.
As with the previous implementation, this may need changes in the future
if the kernel interface changes again.

Note:
This is a proposal for a simpler way of integrating linux kernel changes
in lttng-modules. The implementation is very simple due to the fact that
tid_t was introduced everywhere in one commit in
include/trace/events/jbd2.h. 
I would like to get your opinion on this approach. If needed, it can be
improved.

Roxana Nicolescu (1):
  Introduce configure script to describe changes in linux kernel
    interface

 README.md                             |   3 +-
 configure                             |  36 +++++++++
 include/instrumentation/events/jbd2.h | 110 ++++++--------------------
 3 files changed, 61 insertions(+), 88 deletions(-)
 create mode 100755 configure

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2.34.1