feat(time): 新增 sys_time 系统调用 (#1601)

- 实现 time() 系统调用，返回自纪元以来的秒数
- 支持将时间值写入用户空间指针 tloc
- 使用与 gettimeofday 相同的时间源

Signed-off-by: longjin <longjin@DragonOS.org>

Author: fslongjin

kernel/src/time/syscall/mod.rs

@@ -13,6 +13,7 @@ mod sys_getitimer;
 mod sys_gettimeofday;
 mod sys_nanosleep;
 mod sys_setitimer;
+mod sys_time;
 mod sys_timer_create;
 mod sys_timer_delete;
 mod sys_timer_getoverrun;

kernel/src/time/syscall/sys_time.rs

@@ -0,0 +1,45 @@
+use system_error::SystemError;
+
+use crate::arch::interrupt::TrapFrame;
+use crate::arch::syscall::nr::SYS_TIME;
+use crate::syscall::table::{FormattedSyscallParam, Syscall};
+use crate::syscall::user_access::UserBufferWriter;
+
+/// sys_time: time(time_t *tloc) -> time_t
+///
+/// Linux: returns seconds since the Epoch; if tloc != NULL, also stores it.
+pub struct SysTimeHandle;
+
+impl Syscall for SysTimeHandle {
+    fn num_args(&self) -> usize {
+        1
+    }
+
+    fn handle(&self, args: &[usize], frame: &mut TrapFrame) -> Result<usize, SystemError> {
+        let tloc = args[0] as *mut i64;
+
+        // Use the same time source as gettimeofday.
+        let now_ns = crate::time::timekeeping::do_gettimeofday().to_ns();
+        let now_sec = (now_ns / 1_000_000_000) as i64;
+
+        if !tloc.is_null() {
+            let mut w = UserBufferWriter::new(
+                tloc as *mut u8,
+                core::mem::size_of::<i64>(),
+                frame.is_from_user(),
+            )?;
+            w.buffer_protected(0)?.write_one::<i64>(0, &now_sec)?;
+        }
+
+        Ok(now_sec as usize)
+    }
+
+    fn entry_format(&self, args: &[usize]) -> alloc::vec::Vec<FormattedSyscallParam> {
+        alloc::vec![FormattedSyscallParam::new(
+            "tloc",
+            format!("{:#x}", args[0]),
+        )]
+    }
+}
+
+syscall_table_macros::declare_syscall!(SYS_TIME, SysTimeHandle);