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Source document: kernel/syscall/syscall_table.rst
Translation time: 2025-05-19 01:41:32
Translation model: Qwen/Qwen3-8B
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System Call Table Implementation Plan
Overview
classDiagram
class Syscall {
<<trait>>
+num_args() usize
+handle(args, from_user) Result<usize, SystemError>
+entry_format(args) Vec<FormattedSyscallParam>
}
class SyscallHandle {
+nr: usize
+inner_handle: &dyn Syscall
}
class SyscallTable {
-entries: [Option<&SyscallHandle>; 512]
+get(nr) Option<&dyn Syscall>
}
Syscall <|.. SysXXXXXXHandle
SyscallHandle "1" *-- "1" Syscall
SyscallTable "1" *-- "512" SyscallHandle
System Call Table Architecture
Compared to the original approach of dispatching system calls in a single large match statement, this approach uses a trait-based and system call table-based implementation. The main advantages include:
Reduced stack memory usage: Avoids a single large function consuming excessive stack space
Support for parameter printing: Through a unified parameter formatting interface
Better extensibility: Adding new system calls does not require modifying the dispatch logic
Core Design
Syscall Trait
All system call handler functions must implement the Syscall trait:
pub trait Syscall: Send + Sync + 'static {
fn num_args(&self) -> usize;
fn handle(&self, args: &[usize], from_user: bool) -> Result<usize, SystemError>;
fn entry_format(&self, args: &[usize]) -> Vec<FormattedSyscallParam>;
}
num_args(): Returns the number of arguments required by the system call
handle(): Executes the actual system call handling
entry_format(): Formats the parameters for debugging printing
SyscallHandle
The SyscallHandle struct associates a system call number with its handler:
pub struct SyscallHandle {
pub nr: usize, // System call number
pub inner_handle: &'static dyn Syscall, // Handler function
pub name: &'static str,
}
SyscallTable
The SyscallTable manages all system calls:
Fixed size of 512 entries
Initialized at compile time
Allows quick lookup of the handler function by system call number
Usage
Implementing a System Call
Define the implementation of Syscall for the specific system call
Register the system call in the system call table
Load all registered system calls during system initialization