Add compile-time configuration options for counts and buffer sizes.

Author: Dirbaio

Cargo.toml

@@ -80,6 +80,141 @@ default = [
 
 "_proto-fragmentation" = []
 
+# BEGIN AUTOGENERATED CONFIG FEATURES
+# Generated by gen_config.py. DO NOT EDIT.
+iface-max-addr-count-1 = []
+iface-max-addr-count-2 = [] # Default
+iface-max-addr-count-3 = []
+iface-max-addr-count-4 = []
+iface-max-addr-count-5 = []
+iface-max-addr-count-6 = []
+iface-max-addr-count-7 = []
+iface-max-addr-count-8 = []
+
+iface-max-multicast-group-count-1 = []
+iface-max-multicast-group-count-2 = []
+iface-max-multicast-group-count-3 = []
+iface-max-multicast-group-count-4 = [] # Default
+iface-max-multicast-group-count-5 = []
+iface-max-multicast-group-count-6 = []
+iface-max-multicast-group-count-7 = []
+iface-max-multicast-group-count-8 = []
+iface-max-multicast-group-count-16 = []
+iface-max-multicast-group-count-32 = []
+iface-max-multicast-group-count-64 = []
+iface-max-multicast-group-count-128 = []
+iface-max-multicast-group-count-256 = []
+iface-max-multicast-group-count-512 = []
+iface-max-multicast-group-count-1024 = []
+
+iface-max-sixlowpan-address-context-count-1 = []
+iface-max-sixlowpan-address-context-count-2 = []
+iface-max-sixlowpan-address-context-count-3 = []
+iface-max-sixlowpan-address-context-count-4 = [] # Default
+iface-max-sixlowpan-address-context-count-5 = []
+iface-max-sixlowpan-address-context-count-6 = []
+iface-max-sixlowpan-address-context-count-7 = []
+iface-max-sixlowpan-address-context-count-8 = []
+iface-max-sixlowpan-address-context-count-16 = []
+iface-max-sixlowpan-address-context-count-32 = []
+iface-max-sixlowpan-address-context-count-64 = []
+iface-max-sixlowpan-address-context-count-128 = []
+iface-max-sixlowpan-address-context-count-256 = []
+iface-max-sixlowpan-address-context-count-512 = []
+iface-max-sixlowpan-address-context-count-1024 = []
+
+iface-neighbor-cache-count-1 = []
+iface-neighbor-cache-count-2 = []
+iface-neighbor-cache-count-3 = []
+iface-neighbor-cache-count-4 = [] # Default
+iface-neighbor-cache-count-5 = []
+iface-neighbor-cache-count-6 = []
+iface-neighbor-cache-count-7 = []
+iface-neighbor-cache-count-8 = []
+iface-neighbor-cache-count-16 = []
+iface-neighbor-cache-count-32 = []
+iface-neighbor-cache-count-64 = []
+iface-neighbor-cache-count-128 = []
+iface-neighbor-cache-count-256 = []
+iface-neighbor-cache-count-512 = []
+iface-neighbor-cache-count-1024 = []
+
+iface-max-route-count-1 = []
+iface-max-route-count-2 = [] # Default
+iface-max-route-count-3 = []
+iface-max-route-count-4 = []
+iface-max-route-count-5 = []
+iface-max-route-count-6 = []
+iface-max-route-count-7 = []
+iface-max-route-count-8 = []
+iface-max-route-count-16 = []
+iface-max-route-count-32 = []
+iface-max-route-count-64 = []
+iface-max-route-count-128 = []
+iface-max-route-count-256 = []
+iface-max-route-count-512 = []
+iface-max-route-count-1024 = []
+
+fragmentation-buffer-size-256 = []
+fragmentation-buffer-size-512 = []
+fragmentation-buffer-size-1024 = []
+fragmentation-buffer-size-1500 = [] # Default
+fragmentation-buffer-size-2048 = []
+fragmentation-buffer-size-4096 = []
+fragmentation-buffer-size-8192 = []
+fragmentation-buffer-size-16384 = []
+fragmentation-buffer-size-32768 = []
+fragmentation-buffer-size-65536 = []
+
+assembler-max-segment-count-1 = []
+assembler-max-segment-count-2 = []
+assembler-max-segment-count-3 = []
+assembler-max-segment-count-4 = [] # Default
+assembler-max-segment-count-8 = []
+assembler-max-segment-count-16 = []
+assembler-max-segment-count-32 = []
+
+reassembly-buffer-size-256 = []
+reassembly-buffer-size-512 = []
+reassembly-buffer-size-1024 = []
+reassembly-buffer-size-1500 = [] # Default
+reassembly-buffer-size-2048 = []
+reassembly-buffer-size-4096 = []
+reassembly-buffer-size-8192 = []
+reassembly-buffer-size-16384 = []
+reassembly-buffer-size-32768 = []
+reassembly-buffer-size-65536 = []
+
+reassembly-buffer-count-1 = [] # Default
+reassembly-buffer-count-2 = []
+reassembly-buffer-count-3 = []
+reassembly-buffer-count-4 = []
+reassembly-buffer-count-8 = []
+reassembly-buffer-count-16 = []
+reassembly-buffer-count-32 = []
+
+dns-max-result-count-1 = [] # Default
+dns-max-result-count-2 = []
+dns-max-result-count-3 = []
+dns-max-result-count-4 = []
+dns-max-result-count-8 = []
+dns-max-result-count-16 = []
+dns-max-result-count-32 = []
+
+dns-max-server-count-1 = [] # Default
+dns-max-server-count-2 = []
+dns-max-server-count-3 = []
+dns-max-server-count-4 = []
+dns-max-server-count-8 = []
+dns-max-server-count-16 = []
+dns-max-server-count-32 = []
+
+dns-max-name-size-64 = []
+dns-max-name-size-128 = []
+dns-max-name-size-255 = [] # Default
+
+# END AUTOGENERATED CONFIG FEATURES
+
 [[example]]
 name = "packet2pcap"
 path = "utils/packet2pcap.rs"

README.md

@@ -147,6 +147,8 @@ You probably want to disable default features and configure them one by one:
 smoltcp = { version = "0.8.0", default-features = false, features = ["log"] }
 ```
 
+## Feature flags
+
 ### Feature `std`
 
 The `std` feature enables use of objects and slices owned by the networking stack through a
@@ -195,7 +197,7 @@ Enable `smoltcp::phy::RawSocket` and `smoltcp::phy::TunTapInterface`, respective
 
 These features are enabled by default.
 
-### Features `socket-raw`, `socket-udp`, `socket-tcp`, `socket-icmp`, `socket-dhcpv4`
+### Features `socket-raw`, `socket-udp`, `socket-tcp`, `socket-icmp`, `socket-dhcpv4`, `socket-dns`
 
 Enable the corresponding socket type.
 
@@ -208,6 +210,73 @@ Enable [IPv4] and [IPv6] respectively.
 [IPv4]: https://tools.ietf.org/rfc/rfc791.txt
 [IPv6]: https://tools.ietf.org/rfc/rfc8200.txt
 
+## Configuration
+
+_smoltcp_ has some configuration settings that are set at compile time, affecting sizes
+and counts of buffers.
+
+They can be set in two ways:
+
+- Via Cargo features: enable a feature like `<name>-<value>`. `name` must be in lowercase and
+use dashes instead of underscores. For example. `iface-max-addr-count-3`. Only a selection of values
+is available, check `Cargo.toml` for the list.
+- Via environment variables at build time: set the variable named `SMOLTCP_<value>`. For example 
+`SMOLTCP_IFACE_MAX_ADDR_COUNT=3 cargo build`. You can also set them in the `[env]` section of `.cargo/config.toml`. 
+Any value can be set, unlike with Cargo features.
+
+Environment variables take precedence over Cargo features. If two Cargo features are enabled for the same setting
+with different values, compilation fails.
+
+### IFACE_MAX_ADDR_COUNT
+
+Max amount of IP addresses that can be assigned to one interface (counting both IPv4 and IPv6 addresses). Default: 2.
+
+### IFACE_MAX_MULTICAST_GROUP_COUNT
+
+Max amount of multicast groups that can be joined by one interface. Default: 4.
+
+### IFACE_MAX_SIXLOWPAN_ADDRESS_CONTEXT_COUNT
+
+Max amount of 6LoWPAN address contexts that can be assigned to one interface. Default: 4.
+
+### IFACE_NEIGHBOR_CACHE_COUNT
+
+Amount of "IP address -> hardware address" entries the neighbor cache (also known as the "ARP cache" or the "ARP table") holds. Default: 4.
+
+### IFACE_MAX_ROUTE_COUNT
+
+Max amount of routes that can be added to one interface. Includes the default route. Includes both IPv4 and IPv6. Default: 2.
+
+### FRAGMENTATION_BUFFER_SIZE
+
+Size of the buffer used for fragmenting outgoing packets larger than the MTU. Packets larger than this setting will be dropped instead of fragmented. Default: 1500.
+
+### ASSEMBLER_MAX_SEGMENT_COUNT
+
+Maximum number of non-contiguous segments the assembler can hold. Used for both packet reassembly and TCP stream reassembly. Default: 4.
+
+### REASSEMBLY_BUFFER_SIZE
+
+Size of the buffer used for reassembling (de-fragmenting) incoming packets. If the reassembled packet is larger than this setting, it will be dropped instead of reassembled. Default: 1500.
+
+### REASSEMBLY_BUFFER_COUNT
+
+Number of reassembly buffers, i.e how many different incoming packets can be reassembled at the same time. Default: 1.
+
+### DNS_MAX_RESULT_COUNT
+
+Maximum amount of address results for a given DNS query that will be kept. For example, if this is set to 2 and the queried name has 4 `A` records, only the first 2 will be returned. Default: 1.
+
+### DNS_MAX_SERVER_COUNT
+
+Maximum amount of DNS servers that can be configured in one DNS socket. Default: 1.
+
+### DNS_MAX_NAME_SIZE
+
+Maximum length of DNS names that can be queried. Default: 255.
+
+
+
 ## Hosted usage examples
 
 _smoltcp_, being a freestanding networking stack, needs to be able to transmit and receive

build.rs

@@ -0,0 +1,101 @@
+use std::collections::HashMap;
+use std::fmt::Write;
+use std::path::PathBuf;
+use std::{env, fs};
+
+static CONFIGS: &[(&str, usize)] = &[
+    // BEGIN AUTOGENERATED CONFIG FEATURES
+    // Generated by gen_config.py. DO NOT EDIT.
+    ("IFACE_MAX_ADDR_COUNT", 2),
+    ("IFACE_MAX_MULTICAST_GROUP_COUNT", 4),
+    ("IFACE_MAX_SIXLOWPAN_ADDRESS_CONTEXT_COUNT", 4),
+    ("IFACE_NEIGHBOR_CACHE_COUNT", 4),
+    ("IFACE_MAX_ROUTE_COUNT", 2),
+    ("FRAGMENTATION_BUFFER_SIZE", 1500),
+    ("ASSEMBLER_MAX_SEGMENT_COUNT", 4),
+    ("REASSEMBLY_BUFFER_SIZE", 1500),
+    ("REASSEMBLY_BUFFER_COUNT", 1),
+    ("DNS_MAX_RESULT_COUNT", 1),
+    ("DNS_MAX_SERVER_COUNT", 1),
+    ("DNS_MAX_NAME_SIZE", 255),
+    // END AUTOGENERATED CONFIG FEATURES
+];
+
+struct ConfigState {
+    value: usize,
+    seen_feature: bool,
+    seen_env: bool,
+}
+
+fn main() {
+    // only rebuild if build.rs changed. Otherwise Cargo will rebuild if any
+    // other file changed.
+    println!("cargo:rerun-if-changed=build.rs");
+
+    // Rebuild if config envvar changed.
+    for (name, _) in CONFIGS {
+        println!("cargo:rerun-if-env-changed=SMOLTCP_{name}");
+    }
+
+    let mut configs = HashMap::new();
+    for (name, default) in CONFIGS {
+        configs.insert(
+            *name,
+            ConfigState {
+                value: *default,
+                seen_env: false,
+                seen_feature: false,
+            },
+        );
+    }
+
+    for (var, value) in env::vars() {
+        if let Some(name) = var.strip_prefix("SMOLTCP_") {
+            let Some(cfg) = configs.get_mut(name) else {
+                panic!("Unknown env var {name}")
+            };
+
+            let Ok(value) = value.parse::<usize>() else {
+                panic!("Invalid value for env var {name}: {value}")
+            };
+
+            cfg.value = value;
+            cfg.seen_env = true;
+        }
+
+        if let Some(feature) = var.strip_prefix("CARGO_FEATURE_") {
+            if let Some(i) = feature.rfind('_') {
+                let name = &feature[..i];
+                let value = &feature[i + 1..];
+                if let Some(cfg) = configs.get_mut(name) {
+                    let Ok(value) = value.parse::<usize>() else {
+                        panic!("Invalid value for feature {name}: {value}")
+                    };
+
+                    // envvars take priority.
+                    if !cfg.seen_env {
+                        if cfg.seen_feature {
+                            panic!(
+                                "multiple values set for feature {}: {} and {}",
+                                name, cfg.value, value
+                            );
+                        }
+
+                        cfg.value = value;
+                        cfg.seen_feature = true;
+                    }
+                }
+            }
+        }
+    }
+
+    let mut data = String::new();
+
+    for (name, cfg) in &configs {
+        writeln!(&mut data, "pub const {}: usize = {};", name, cfg.value).unwrap();
+    }
+
+    let out_dir = PathBuf::from(env::var_os("OUT_DIR").unwrap());
+    let out_file = out_dir.join("config.rs").to_string_lossy().to_string();
+    fs::write(out_file, data).unwrap();
+}