linux VS magic-trace

>A pidfd does not let you hold a reference to an individual thread, only to a process

I think that's outdated: https://github.com/torvalds/linux/commit/64bef697d33b75fc06c...

For specific cases I can find ext4 explicitly checking for RO https://github.com/torvalds/linux/blob/8c06da67d0bd3139a97f3...

FFS predates FreeBSD and is in some capacity supported by all 3 major BSDs. I'm fairly confident that Linux actually supports it through the ufs driver ( https://github.com/torvalds/linux/tree/master/fs/ufs ); whether the use of different names in different places makes it better or worse is an exercise for the reader.

These are a bit easier to see what's going on:

https://github.com/torvalds/linux/commit/d5cf50dafc9dd5faa1e...

https://github.com/torvalds/linux/blob/d5cf50dafc9dd5faa1e61...

Unfortunately Github doesn't have a way to render symbols for whitespace, but you can tell by selecting the spaces that the previous version had leading tabs. Linus changed it so that the tokens `default` and the number e.g. `12` are also separated by a tab. This is tricky, because the token "default" is seven characters, it will always give this added tab a width of 1 char which makes it always layout the same as if it were a space no matter if you use tab widths of 1, 2, 4, or 8.

There was also a Gentoo effort to run atop FreeBSD[0]. The challenge of course is that afaik none of the BSD kernel ABIs are considered stable. The stable interface is the BSD libc. That said, with binfmt_misc, I don't see a reason you couldn't just run (at least some) FreeBSD binaries on Linux with a thin syscall translation layer (rather something like qemu-system) and then your layer hooked via binfmt_misc. I'm not aware of anyone who has done this for FreeBSD, but prior efforts existed as alternate binfmts for SysVr4/5 ELF binaries[2]. Either way would take some elbow grease, but you *might* even be able just reuse binfmt_elf and just have a new interpreter for FreeBSD elf.

[0] https://wiki.gentoo.org/wiki/Gentoo_FreeBSD

[1] https://docs.kernel.org/admin-guide/binfmt-misc.html

[2] https://github.com/torvalds/linux/blob/master/fs/binfmt_elf....

I really like magic-trace [0].

https://github.com/janestreet/magic-trace

Not that the exact tracing relies on Intel PT - support for AMD was added recently but uses perf so suffers from the same sampling/skew issues, but is still very useful.

Would love to see this integrate with magic trace [1]. I'll need to look at the code for the flamegraph plugin, because handling nanosecond timestamps in flamegraphs seems to break most tools due to float precision.

(1) https://github.com/janestreet/magic-trace

As for inner workings, have you looked into magic trace? I want to play around with it but last I checked, it doesn't work on macs.

I really hope he can work with cloud vendors and Intel to make Processor Trace a more popular and easier to use capability.

It's unfortunate how https://github.com/janestreet/magic-trace and PMUs in general can't be used by lots of people using cloud VMs.

Magic-trace – High-resolution traces of what a process is doing\ (133 comments)