tests: Resize the pipe size to 256K for capturing child stdout/err

As discussed in #1707, the `vcpu` thread can be stalled when using
`--serial tty`. To workaround that issue, this patch enforces to resize
the pipe size to 256K when we capture the stdout/stderr of the
cloud-hypervisor child process in the integration tests. Note that the
pipe size (256K) is chosen based on the output size of our integration
tests at this point, which may need to be increased in the future.

Signed-off-by: Bo Chen <chen.bo@intel.com>

tests/integration.rs

@@ -24,6 +24,7 @@ mod tests {
     use std::io::BufRead;
     use std::io::{Read, Write};
     use std::net::TcpStream;
+    use std::os::unix::io::AsRawFd;
     use std::path::{Path, PathBuf};
     use std::process::{Child, Command, Stdio};
     use std::string::String;
@@ -90,6 +91,8 @@ mod tests {
 
     const DIRECT_KERNEL_BOOT_CMDLINE: &str = "root=/dev/vda1 console=ttyS0 console=hvc0 quiet rw";
 
+    const PIPE_SIZE: i32 = 256 << 10;
+
     impl UbuntuDiskConfig {
         fn new(image_name: String) -> Self {
             UbuntuDiskConfig {
@@ -978,10 +981,26 @@ mod tests {
 
         fn spawn(&mut self) -> io::Result<Child> {
             if self.capture_output {
-                self.command
+                let child = self
+                    .command
                     .stderr(Stdio::piped())
                     .stdout(Stdio::piped())
                     .spawn()
+                    .unwrap();
+
+                let fd = child.stdout.as_ref().unwrap().as_raw_fd();
+                let pipesize = unsafe { libc::fcntl(fd, libc::F_SETPIPE_SZ, PIPE_SIZE) };
+                let fd = child.stderr.as_ref().unwrap().as_raw_fd();
+                let pipesize1 = unsafe { libc::fcntl(fd, libc::F_SETPIPE_SZ, PIPE_SIZE) };
+
+                if pipesize >= PIPE_SIZE && pipesize1 >= PIPE_SIZE {
+                    Ok(child)
+                } else {
+                    Err(std::io::Error::new(
+                        std::io::ErrorKind::Other,
+                        "resizing pipe w/ 'fnctl' failed!",
+                    ))
+                }
             } else {
                 self.command.spawn()
             }