Regressed by b469d9e9aa53. Affects downstream package. CC @unrelentingtech

• FreeBSD >= 13.0 has memfd_create(3) but https://github.com/rust-lang/libc/commit/0a57541a7101 cannot be used due to https://github.com/rust-lang/libc/issues/570. memfd_create can be replaced with shm_open(SHM_ANON, ...) which is supported on all FreeBSD versions.
• OpenBSD has shm_mkstemp(3) but not exposed in libc crate
• DragonFly and NetBSD have neither

$ cargo build
[...]
error[E0433]: failed to resolve: could not find `MemfdOptions` in `memfd`
   --> src/wayland.rs:106:39
    |
106 |                     let file = memfd::MemfdOptions::new().create("ramp")?;
    |                                       ^^^^^^^^^^^^ could not find `MemfdOptions` in `memfd`

warning: unused import: `std::os::unix::io::AsRawFd`
  --> src/wayland.rs:12:5
   |
12 | use std::os::unix::io::AsRawFd;
   |     ^^^^^^^^^^^^^^^^^^^^^^^^^^
   |
   = note: `#[warn(unused_imports)]` on by default

For more information about this error, try `rustc --explain E0433`.
warning: `wl-gammarelay-rs` (bin "wl-gammarelay-rs") generated 1 warning
error: could not compile `wl-gammarelay-rs` due to previous error; 1 warning emitted

Output of rustup check: stable-x86_64-unknown-linux-gnu - Up to date : 1.58.1 (db9d1b20b 2022-01-20) rustup - Up to date : 1.24.3

error[E0005]: refutable pattern in local binding: `_` not covered
 --> ~/.cargo/registry/src/github.com-1ecc6299db9ec823/wl-gammarelay-rs-0.2.0/src/dbus_client.rs:6:9
  |
6 |     let zbus::Address::Unix(addr) = zbus::Address::session()?;
  |         ^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `_` not covered
  |
  = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
  = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
  = note: the matched value is of type `zbus::Address`
help: you might want to use `if let` to ignore the variant that isn't matched
  |
6 |     if let zbus::Address::Unix(addr) = zbus::Address::session()? { /* */ }
  |

error[E0005]: refutable pattern in local binding: `_` not covered
  --> ~/.cargo/registry/src/github.com-1ecc6299db9ec823/wl-gammarelay-rs-0.2.0/src/dbus_server.rs:14:9
   |
14 |     let zbus::Address::Unix(addr) = zbus::Address::session()?;
   |         ^^^^^^^^^^^^^^^^^^^^^^^^^ pattern `_` not covered
   |
   = note: `let` bindings require an "irrefutable pattern", like a `struct` or an `enum` with only one variant
   = note: for more information, visit https://doc.rust-lang.org/book/ch18-02-refutability.html
   = note: the matched value is of type `zbus::Address`
help: you might want to use `if let` to ignore the variant that isn't matched
   |
14 |     if let zbus::Address::Unix(addr) = zbus::Address::session()? { /* */ }
   |

For more information about this error, try `rustc --explain E0005`.
error: failed to compile `wl-gammarelay-rs v0.2.0`, intermediate artifacts can be found at `/tmp/cargo-installhvl4E7`

Caused by:
  could not compile `wl-gammarelay-rs` due to 2 previous errors

My use case: I like to adjust the color temperature of my display (redhift style). I also frequently invert the colors of my display (by keystroke) because I visually prefer light-on-dark but have to look a lot at black-on-white documents.

However, currently, adjusting the color temperature and inverting the display do not properly combine, as effectively the temperature-adjusted gamma ramp is inverted. This is because the gamma ramp is inverted upside-down:

r[i] = u16::MAX - (v * white_r) as u16;

To properly temperature-adjust the inverted gamma ramp, one should instead flip the gamma ramp left-to-right:

r[ramp_size - 1 - i] = (v * white_r) as u16;

With a linear gamma ramp and full brightness, both methods of course have the same effect. With a linear gamma ramp and reduced brightness setting, the original increases brightness due to the inversion (turning black into gray), while my proposed method reduces brightness even under inversion.

Changing the behavior as I propose would probably destroy other users' use cases. But would you accept a patch that adds this behavior as a new option?

This works flawlessly for me, but check carefully - this is my first hackery in Rust, and I don't know Rust.

You probably want to squash the commits (sorry) on merging.

As an aside, I noticed that the symbols in the Waybar example (where Gamma uses γ) use Unicode code points from a private use area and are thus unlikely to be displayed properly for many users (including me).