bindings: rust: document build without install

While the Makefile does this automatically, a user may want to do
something similar for other cargo commands.

Reported-by: Kent Gibson <warthog618@gmail.com>
Link: https://lore.kernel.org/r/ZIQJquwzNacp1Nuh@sol/
Signed-off-by: Erik Schilling <erik.schilling@linaro.org>
Acked-by: Viresh Kumar <viresh.kumar@linaro.org>
Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>

diff --git a/bindings/rust/libgpiod-sys/README.md b/bindings/rust/libgpiod-sys/README.md
index 90198d813c90ff27b443554a1f39b8eb3623dc46..f9db496287c3e72c62ffca1bad63a04c742282a3 100644 (file)
--- a/bindings/rust/libgpiod-sys/README.md
+++ b/bindings/rust/libgpiod-sys/README.md
@@ -16,6 +16,15 @@ libs and headers by setting environment variables. The mechanism for that is
 documented in the
 [system_deps crate documentation](https://docs.rs/system-deps/6.1.0/system_deps/#overriding-build-flags).
 
+If installing libgpiod is undesired, one can set the following environent
+variables in order to build against the intermediate build results of a `make`
+build of the C lib (paths are relative to the Cargo.toml):
+
+       export SYSTEM_DEPS_LIBGPIOD_NO_PKG_CONFIG=1
+       export SYSTEM_DEPS_LIBGPIOD_SEARCH_NATIVE="<PATH-TO-LIBGPIOD>/lib/.libs/"
+       export SYSTEM_DEPS_LIBGPIOD_LIB=gpiod
+       export SYSTEM_DEPS_LIBGPIOD_INCLUDE="<PATH-TO-LIBGPIOD>/include/"
+
 ## License
 
 This project is licensed under either of