From 6dc0a22ebb0f9a6edbf054de3a50bd69b0e82e48 Mon Sep 17 00:00:00 2001
From: Aditya Bommakanti <64078333+VNSAditya02@users.noreply.github.com>
Date: Tue, 13 Sep 2022 00:32:56 +0530
Subject: [PATCH] Description of src/vmm/src/config/mod.rs

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 mod.md | 135 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 135 insertions(+)
 create mode 100644 mod.md

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+## Description of [src/vmm/src/config/mod.rs](https://github.com/codenet/vmm-reference/blob/main/src/vmm/src/config/mod.rs)
+The VMMConfig struct implemented in this file is used in [main.rs](https://github.com/codenet/vmm-reference/blob/main/src/main.rs) file. If all the configurations are valid, then VM starts running.
+This code uses CfgArgParser defined in [arg_parser.rs](https://github.com/codenet/vmm-reference/blob/main/src/vmm/src/config/arg_parser.rs). The CggArgParser is defined as below. It has a HashMap which stores 'parameter name' as key and the 'value of parameter' as value. The 'value_of' method defined in 'arg_parser.rs' file is used to get the value for a given parameter name.
+```rs
+pub(super) struct CfgArgParser {
+    args: HashMap<String, String>,
+}
+```
+
+These are the possible errors while converting the *Config objects. There can be parsing errors while configuring Kernel, Memory, Vcpus, Network, Block
+```rs
+pub enum ConversionError {
+    /// Failed to parse the string representation for the kernel.
+    ParseKernel(String),
+    /// Failed to parse the string representation for guest memory.
+    ParseMemory(String),
+    /// Failed to parse the string representation for the vCPUs.
+    ParseVcpus(String),
+    /// Failed to parse the string representation for the network.
+    ParseNet(String),
+    /// Failed to parse the string representation for the block.
+    ParseBlock(String),
+}
+```
+
+The MemoryConfig struct store size of Guest Memory (which is of type u32) in MiB. By default, the size is 256MiB
+```rs
+pub struct MemoryConfig {
+    /// Guest memory size in MiB.
+    pub size_mib: u32,
+}
+
+impl Default for MemoryConfig {
+    fn default() -> Self {
+        MemoryConfig { size_mib: 256u32 }
+    }
+}
+```
+
+The string argument for Memory configuration is parsed using CfgArgParser. Then, it call 'value_of' method of arg_parser which parameter name 'size_mib' as argument. The converted value is saved in size_mb. It will raise a ConversionError if there is an error while parsing.
+```rs
+impl TryFrom<&str> for MemoryConfig {
+    type Error = ConversionError;
+
+    fn try_from(mem_cfg_str: &str) -> result::Result<Self, Self::Error> {
+        // Supported options: `size=<u32>`
+        let mut arg_parser = CfgArgParser::new(mem_cfg_str);
+
+        let size_mib = arg_parser
+            .value_of("size_mib")
+            .map_err(ConversionError::new_memory)?
+            .unwrap_or(256);
+        arg_parser
+            .all_consumed()
+            .map_err(ConversionError::new_memory)?;
+        Ok(MemoryConfig { size_mib })
+    }
+}
+```
+The VcpuConfig struct stores the number of Virtual CPUs (which is of type u8). By default, num = 1 
+```rs
+pub struct VcpuConfig {
+    /// Number of vCPUs.
+    pub num: u8,
+}
+
+impl Default for VcpuConfig {
+    fn default() -> Self {
+        VcpuConfig { num: 1u8 }
+    }
+}
+```
+
+Similar to the case of MemoryConfig, this uses CfgArgParser to parse. Here, argument to 'value_of' method is "num" 
+```rs
+impl TryFrom<&str> for VcpuConfig {
+    type Error = ConversionError;
+
+    fn try_from(vcpu_cfg_str: &str) -> result::Result<Self, Self::Error> {
+        // Supported options: `num=<u8>`
+        let mut arg_parser = CfgArgParser::new(vcpu_cfg_str);
+        let num = arg_parser
+            .value_of("num")
+            .map_err(ConversionError::new_vcpus)?
+            .unwrap_or_else(|| num::NonZeroU8::new(1).unwrap());
+        arg_parser
+            .all_consumed()
+            .map_err(ConversionError::new_vcpus)?;
+        Ok(VcpuConfig { num: num.into() })
+    }
+}
+```
+The KernelConfig struct store cmdline (Kernel Command line), path (path to the kernel image) and load_addr (the address where kernel should be loaded). In try_from method of this struct, it parses the string using CfgArgParser. Then gets these three attributes by passing 'cmdline', 'path', 'kernel_load_addr' as parameters respectively to 'value_of' method.
+```rs
+pub struct KernelConfig {
+    /// Kernel command line.
+    pub cmdline: Cmdline,
+    /// Path to the kernel image.
+    pub path: PathBuf,
+    /// Address where the kernel is loaded.
+    pub load_addr: u64,
+}
+```
+
+The NetConfig struct store tap_name, which is the name of tap_device. In try_from method of this struct, it parses the string using CfgArgParser. Then gets these three attributes by passing 'tap' as parameter to 'value_of' method.
+```rs
+pub struct NetConfig {
+    /// Name of tap device.
+    pub tap_name: String,
+}
+```
+
+The BlockConfig struct stores pub path, which is the path to block device. Then gets these three attributes by passing 'path' as parameter to 'value_of' method in 'try_from' method.
+```rs
+pub struct BlockConfig {
+    /// Path to the block device backend.
+    pub path: PathBuf,
+}
+```
+
+The VMMConfig struct stores the configurations of VMM. It stores the Memory, vCPU, kernel, Network device, Block device configurations.
+```rs
+pub struct VMMConfig {
+    /// Guest memory configuration.
+    pub memory_config: MemoryConfig,
+    /// vCPU configuration.
+    pub vcpu_config: VcpuConfig,
+    /// Guest kernel configuration.
+    pub kernel_config: KernelConfig,
+    /// Network device configuration.
+    pub net_config: Option<NetConfig>,
+    /// Block device configuration.
+    pub block_config: Option<BlockConfig>,
+}
+```
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