test: run mkdir before mounting if necessary

crates/nit/src/system/mod.rs

@@ -7,7 +7,11 @@ pub mod syscall;
 pub fn dmesg(value: impl std::fmt::Display) {
     let timespec = syscall::clock_gettime(libc::CLOCK_BOOTTIME).unwrap();
     for line in value.to_string().lines() {
-        eprintln!("[{: >5}.{}] {line}", timespec.tv_sec, timespec.tv_nsec / 1000);
+        eprintln!(
+            "[{: >5}.{}] {line}",
+            timespec.tv_sec,
+            timespec.tv_nsec / 1000
+        );
     }
 }
 
@@ -69,6 +73,13 @@ impl Mount {
     }
 
     pub fn mount_self(&self) -> Result<()> {
+        if !std::fs::exists(&self.target).context(format_args!(
+            "could not check if path exists: {path}",
+            path = self.target.display()
+        ))? {
+            syscall::mkdir(&self.target)?;
+        }
+
         dmesg(format!(
             "Mounting {source} to {target}",
             source = self.source.display(),

crates/nit/src/system/syscall.rs

@@ -89,6 +89,21 @@ pub fn mount(
     }
 }
 
+pub fn mkdir(path: impl AsRef<Path>) -> Result<()> {
+    let path = path.as_ref();
+    let path_cs = CString::new(path.as_os_str().as_encoded_bytes())
+        .context(format_args!("bad path: {path}", path = path.display()))?;
+
+    match unsafe { libc::mkdir(path_cs.as_ptr(), 0o755) } {
+        0 => Ok(()),
+        -1 => ctx_os_error(format_args!(
+            "error calling mkdir({path}, 0o755)",
+            path = path.display()
+        )),
+        n => unreachable!("mount() syscall returned bad value: {n}"),
+    }
+}
+
 pub fn freopen(path: impl AsRef<Path>, mode: impl AsRef<str>, fd: &impl AsRawFd) -> Result<()> {
     let path = path.as_ref();
     let mode = mode.as_ref();