FreeBSD: Use a statement expression to implement SET_ERROR() #16284
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This way we can avoid making assumptions about the SDT probe implementation. No functional change intended. Signed-off-by: Mark Johnston <[email protected]>
This way we can avoid making assumptions about the SDT probe implementation. No functional change intended. This was submitted upstream as openzfs/zfs#16284
This way we can avoid making assumptions about the SDT probe implementation. No functional change intended. This was submitted upstream as openzfs/zfs#16284 MFC after: 1 week
The difference is just that SDT_* makes you define a probe's argument types in advance, while DTRACE_PROBE* does everything in one statement. So, DTRACE_PROBE* is more useful for ad-hoc tracing, while SDT_* lets you collect probe definitions and argument types in one place. It is a bit of an odd difference. It occurs also partly because DTRACE_PROBE* comes from illumos, while SDT_* is a FreeBSD interface. At some point we (FreeBSD) should try to unify them, but it is not much of a priority for me at the moment. From my POV, using SDT_* for SET_ERROR() makes some sense, since this macro is used frequently. If it was replaced with DTRACE_PROBE*, we'd just end up bloating zfs.ko a bit with redundant probe definitions. |
Use a statement expression to implement SET_ERROR().
Motivation and Context
The current implementation makes assumptions about how SDT_PROBE* is implemented on FreeBSD. These assumptions will become false after a forthcoming FreeBSD kernel change.
Description
SET_ERROR() can be implemented using a statement expression in a way that avoids making assumptions about SDT internals. OpenZFS uses statement expressions elsewhere in the kernel module, so I presume that doing so here is allowed.
How Has This Been Tested?
Interactively, using
dtrace -n 'sdt:::set-error {printf("%d", args[0]); stack();}'and using a kernel debugger to validate dtrace's output.Types of changes
Checklist:
Signed-off-by.