Add nix processes command

[matthewbauer]

adds a processes command for #3751

some thing still missing:

• mostly relies on procfs for cmdline info
• no phase reporting

output looks like:

Build User: nixbld1
Build Process: nix-daemon 3535     
Child Process: /nix/store/b3zsk4ihlpiimv3vff86bb5bxghgdzb9-gcc-9.2.0/libexec/gcc/x86_64-unknown-linux-gnu/9.2.0/cc1 -quiet -D _FORTIFY_SOURCE=2 -idirafter /nix/store/fwpn2f7a4iqszyydw7ag61zlnp6xk5d3-glibc-2.30-dev/include -idirafter /nix/store/b3zsk4ihlpiimv3vff86bb5bxghgdzb9-gcc-9.2.0/lib/gcc/x86_64-unknown-linux-gnu/9.2.0/include-fixed conftest.c -quiet -dumpbase conftest.c -mtune=generic -march=x86-64 -auxbase conftest -g -O2 -O2 -Wformat=1 -Wformat-security -Werror=format-security -fstack-protector-strong -fno-strict-overflow -fPIC --param ssp-buffer-size=4 -o /build/cceFfp2A.s 
File Lock: /nix/store/l285fr6qxcf0v0iaphs38lcghv206zar-hello-2.10.lock

[matthewbauer]

Ok - this actually doesn't quite work. The userpool locks are always owned by the same process in the nix-daemon. We'll need to filter by uid to determine what the actual pid is.

[matthewbauer]

Updated to show the correct pid based on uid of the owning process.

[edolstra]

Not sure this is the best approach. 1) It's Linux specific, so at least there should be a big #if __linux__ around it. 2) It only works when using build users. 3) It make the Nix CLI depend on the internals of LocalStore. For instance, it will break once #3600 gets merged. 4) The name nix processes is a bit vague. (What processes?) Maybe something like nix debug show-daemon-status is better.

[michaelpj]

It would be very nice to have a command like this in some form, nix-top is very useful.

As for a name, how about nix daemon status?

[Atemu]

Status makes me think more of "how's the daemon doing, is it still up?" (though that also sounds useful), how about nix daemon monitor?

You'd use the command to monitor what the daemon is up to atm afterall.

[matthewbauer]

Not sure this is the best approach. 1) It's Linux specific, so at least there should be a big #if __linux__ around it.

That sounds alright. Some non-Linux systems have procfs, but I have no idea whether it looks the same.

3. It make the Nix CLI depend on the internals of LocalStore. For instance, it will break once Automatic UID allocation #3600 gets merged.

Right - this is just using the locks in the filesystem. These don't end up being as clear as I originally hoped.

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What approach would be better? We could keep track of it in nix-daemon - which right now doesn't really know about what builds are happening.

[stale]

I marked this as stale due to inactivity. → More info

[Atemu]

Still important to me.

[stale]

I marked this as stale due to inactivity. → More info