On 07/01/22(Fri) 10:54, Sebastien Marie wrote: > Hi, > > Debugging some code paths is complex: for example, unveil(2) code is > involved inside VFS, and using DEBUG_UNVEIL means that the kernel is > spamming printf() for all processes using unveil(2) (a lot of > processes) instead of just the interested cases I want to follow. > > So I cooked the following diff to add a KTRLOG() facility to be able > to replace printf()-like debugging with a more process-limited method.
I wish you could debug such issue without having to change any kernel code that's why I started btrace(8). You should already be able to filter probes per thread/process, maybe you want to replace some debug printf by static probes. Alternatively you could define DDBPROF and use the kprobe provider which allow you to inspect prologue and epilogue of ELF functions. Maybe btrace(8) is not yet fully functional to debug this particular problem, but improving it should hopefully give us a tool to debug most of the kernel issues without having to write a diff and boot a custom kernel. At least that's the goal.
