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Use raw channel fallback if pty setup failed
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In resume mode the firecracker pilot uses a vsock connection
for the host <-> guest data transfer. On the guest the command
is by default called in a new PTY. However if this is not possible
e.g because the guest does not support pty allocation there
should be a fallback allocating the standard channels directly.
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@schaefi
schaefi committed Jan 17, 2024
1 parent b7d4cbc commit ce4b766
Showing 1 changed file with 105 additions and 88 deletions.
193 changes: 105 additions & 88 deletions firecracker-pilot/guestvm-tools/sci/src/main.rs
View file
Original file line number Diff line number Diff line change
Expand Up @@ -379,99 +379,27 @@ fn main() {
do_reboot(ok)
}

fn redirect_command(command: &str, mut stream: vsock::VsockStream) {
fn redirect_command(command: &str, stream: vsock::VsockStream) {
// start the given command as a child process in a new PTY
// or on raw channels if no pseudo terminal can be allocated
// connect its standard channels to the stream
// transfer all channel data when there is data as long as the child exists
let fork = Fork::from_ptmx().unwrap();

if let Ok(mut master) = fork.is_parent() {
let stdout_fd = master.as_raw_fd();
let stream_fd = stream.as_raw_fd();

// main send/recv loop
let mut buffer = [0_u8; 100];
loop {
// prepare file descriptors to be watched for by select()
let raw_fdset = std::mem::MaybeUninit::<libc::fd_set>::uninit();
let mut fdset = unsafe { raw_fdset.assume_init() };
let mut max_fd = -1;
unsafe { libc::FD_ZERO(&mut fdset) };
unsafe { libc::FD_SET(stdout_fd, &mut fdset) };
max_fd = std::cmp::max(max_fd, stdout_fd);
unsafe { libc::FD_SET(stream_fd, &mut fdset) };
max_fd = std::cmp::max(max_fd, stream_fd);

// block this thread until something new happens
// on these file-descriptors
unsafe {
libc::select(
max_fd + 1,
&mut fdset,
std::ptr::null_mut(),
std::ptr::null_mut(),
std::ptr::null_mut()
)
};
// this thread is not blocked any more,
// try to handle what happened on the file descriptors
if unsafe { libc::FD_ISSET(stdout_fd, &fdset) } {
// something new happened on master,
// try to receive some bytes an send them through the stream
if let Ok(sz_r) = master.read(&mut buffer) {
if sz_r == 0 {
debug("EOF detected on stdout");
break;
}
if stream.write_all(&buffer[0..sz_r]).is_err() {
debug("write failure on stream");
break;
}
} else {
debug("read failure on process stdout");
break;
}
}
if unsafe { libc::FD_ISSET(stream_fd, &fdset) } {
// something new happened on the stream
// try to receive some bytes an send them on stdin
if let Ok(sz_r) = stream.read(&mut buffer) {
if sz_r == 0 {
debug("EOF detected on stream");
break;
}
if master.write_all(&buffer[0..sz_r]).is_err() {
debug("write failure on stdin");
break;
}
} else {
debug("read failure on stream");
break;
}
}
}
let _ = fork.wait();
} else {
let mut call_args: Vec<&str> = command.split(' ').collect();
let program = call_args.remove(0);
let mut call = Command::new(program);
for arg in call_args {
call.arg(arg);
}
debug(&format!(
"SCI CALL: {} -> {:?}", program, call.get_args()
));
match call.status() {
Ok(_) => { },
Err(error) => {
debug(&format!(
"SCI guest command failed with: {}", error
));
}
match Fork::from_ptmx() {
Ok(fork) => {
redirect_command_to_pty(command, stream, fork)
},
Err(error) => {
debug(&format!(
"Terminal allocation failed, using raw channels: {:?}", error
));
redirect_command_to_raw_channels(command, stream)
}
}
/* Code without PTY
}

fn redirect_command_to_raw_channels(
command: &str, mut stream: vsock::VsockStream
) {
let mut call_args: Vec<&str> = command.split(' ').collect();
let program = call_args.remove(0);
let mut call = Command::new(program);
Expand Down Expand Up @@ -583,7 +511,96 @@ fn redirect_command(command: &str, mut stream: vsock::VsockStream) {
));
}
}
*/
}

fn redirect_command_to_pty(
command: &str, mut stream: vsock::VsockStream, pty_fork: Fork
) {
if let Ok(mut master) = pty_fork.is_parent() {
let stdout_fd = master.as_raw_fd();
let stream_fd = stream.as_raw_fd();

// main send/recv loop
let mut buffer = [0_u8; 100];
loop {
// prepare file descriptors to be watched for by select()
let raw_fdset = std::mem::MaybeUninit::<libc::fd_set>::uninit();
let mut fdset = unsafe { raw_fdset.assume_init() };
let mut max_fd = -1;
unsafe { libc::FD_ZERO(&mut fdset) };
unsafe { libc::FD_SET(stdout_fd, &mut fdset) };
max_fd = std::cmp::max(max_fd, stdout_fd);
unsafe { libc::FD_SET(stream_fd, &mut fdset) };
max_fd = std::cmp::max(max_fd, stream_fd);

// block this thread until something new happens
// on these file-descriptors
unsafe {
libc::select(
max_fd + 1,
&mut fdset,
std::ptr::null_mut(),
std::ptr::null_mut(),
std::ptr::null_mut()
)
};
// this thread is not blocked any more,
// try to handle what happened on the file descriptors
if unsafe { libc::FD_ISSET(stdout_fd, &fdset) } {
// something new happened on master,
// try to receive some bytes an send them through the stream
if let Ok(sz_r) = master.read(&mut buffer) {
if sz_r == 0 {
debug("EOF detected on stdout");
break;
}
if stream.write_all(&buffer[0..sz_r]).is_err() {
debug("write failure on stream");
break;
}
} else {
debug("read failure on process stdout");
break;
}
}
if unsafe { libc::FD_ISSET(stream_fd, &fdset) } {
// something new happened on the stream
// try to receive some bytes an send them on stdin
if let Ok(sz_r) = stream.read(&mut buffer) {
if sz_r == 0 {
debug("EOF detected on stream");
break;
}
if master.write_all(&buffer[0..sz_r]).is_err() {
debug("write failure on stdin");
break;
}
} else {
debug("read failure on stream");
break;
}
}
}
let _ = pty_fork.wait();
} else {
let mut call_args: Vec<&str> = command.split(' ').collect();
let program = call_args.remove(0);
let mut call = Command::new(program);
for arg in call_args {
call.arg(arg);
}
debug(&format!(
"SCI CALL: {} -> {:?}", program, call.get_args()
));
match call.status() {
Ok(_) => { },
Err(error) => {
debug(&format!(
"SCI guest command failed with: {}", error
));
}
}
}
}

fn do_reboot(ok: bool) {
Expand Down

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