namei: Allow for runtime debug messages in name lookup

[mjg]

Summary

Changed the NAMEI_DIAGNOSIC check to NAMEI_DEBUG instead and added
a kernel config option for it.

Added the vfs.namei_debug sysctl/tunable to control the debug
message output. Default value is the value assigned via the
NAMEI_DEBUG kernel config option.

[mjg]

is this really of practical usage today? i was considering removing these printfs to begin with

[kib]

In D41207#938511, @mjg wrote:

is this really of practical usage today? i was considering removing these printfs to begin with

I agree, better to remove it.

sys/kern/vfs_lookup.c

1118

This code better to be removed. At very least, print cn_name by one char, instead of patching it forth and back.

[stevek]

In D41207#938522, @kib wrote:

In D41207#938511, @mjg wrote:

is this really of practical usage today? i was considering removing these printfs to begin with

I agree, better to remove it.

I'm fine with removing it. We had someone use it recently and I did the change to make it easier to set.
Although I'm not sure how much use it would be, since I would expect it to be rather spammy.

But I think they were having a panic occurring in VFS code and, for some reason, they were not getting into the kernel debugger, even though it was supposed to be enabled. Therefore, they wanted to be able to tell what was being looked up. (Because of the panic, they could not use dtrace, as I would usually suggest.)

I can do the pruning, if you'd like and update this review to instead prune it out.

[mjg]

In D41207#938592, @stevek wrote:

In D41207#938522, @kib wrote:

In D41207#938511, @mjg wrote:

is this really of practical usage today? i was considering removing these printfs to begin with

I agree, better to remove it.

I'm fine with removing it. We had someone use it recently and I did the change to make it easier to set.
Although I'm not sure how much use it would be, since I would expect it to be rather spammy.

But I think they were having a panic occurring in VFS code and, for some reason, they were not getting into the kernel debugger, even though it was supposed to be enabled. Therefore, they wanted to be able to tell what was being looked up. (Because of the panic, they could not use dtrace, as I would usually suggest.)

I can do the pruning, if you'd like and update this review to instead prune it out.

I somehow missed this update.

Please submit a patch whacking this.

In absolute worst case if some printing from namei will be the thing to do, interested parties can trivially patch the kernel as needed.

[mjg]

So I went ahead and whacked this, see https://cgit.FreeBSD.org/src/commit/?id=b8b33f3b3b71ad7b4b5714afec21d6e8ad7fd6ce

As such I think the review can be abandoned.

[mjg]

Given the above I'm closing this.