capsules_core/console_ordered.rs
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// Licensed under the Apache License, Version 2.0 or the MIT License.
// SPDX-License-Identifier: Apache-2.0 OR MIT
// Copyright Tock Contributors 2022.
//! Provides userspace with access to a serial interface whose output
//! is in-order with respect to kernel debug!() operations.
//!
//! Prints to the console are atomic up to particular constant length,
//! which can be set at capsule instantiation.
//!
//! Note that this capsule does *not* buffer writes in an additional
//! buffer; this is critical to ensure ordering. Instead, it pushes
//! writes into the kernel debug buffer. If there is insufficient space
//! in the buffer for the write (or an atomic block size chunk of a very
//! large write), the capsule waits and uses a retry timer. This means
//! that in-kernel debug statements can starve userspace prints, e.g.,
//! if they always keep the kernel debug buffer full.
//!
//! Setup
//! -----
//!
//! This capsule allows userspace programs to print to the kernel
//! debug log. This ensures that (as long as the writes are not
//! truncated) that kernel and userspace print operations are in
//! order. It requires a reference to an Alarm for timers to issue
//! callbacks and send more data. The three configuration constants are:
//! - ATOMIC_SIZE: the minimum block of buffer that will be sent. If
//! there is not enough space in the debug buffer to
//! send ATOMIC_SIZE bytes, the console retries later.
//! - RETRY_TIMER: if there is not enough space in the debug buffer
//! to send the next chunk of a write, the console
//! waits RETRY_TIMER ticks of the supplied alarm.
//! - WRITE_TIMER: after completing a write, the console waits
//! WRITE_TIMER ticks of the supplied alarm before
//! issuing a callback or writing more.
//!
//! RETRY_TIMER and WRITE_TIMER should be set based on the speed of
//! the underlying UART and desired load. Generally speaking, setting
//! them around 50-100 byte times is good. For example, this means on
//! a 115200 UART, setting them to 5ms (576 bits, or 72 bytes) is
//! reasonable. ATOMIC_SIZE should be at least 80 (row width
//! of a standard console).
//!
//! ```rust,ignore
//! # use kernel::static_init;
//! # use capsules_core::console_ordered::ConsoleOrdered;
//! let console = static_init!(
//! ConsoleOrdered,
//! ConsoleOrdered::new(virtual_alarm,
//! board_kernel.create_grant(capsules_core::console_ordered::DRIVER_NUM,
//! &grant_cap),
//! ATOMIC_SIZE,
//! RETRY_TIMER,
//! WRITE_TIMER));
//!
//! ```
//!
//! Usage
//! -----
//!
//! The user must perform three steps in order to write a buffer:
//!
//! ```c
//! // (Optional) Set a callback to be invoked when the buffer has been written
//! subscribe(CONSOLE_DRIVER_NUM, 1, my_callback);
//! // Share the buffer from userspace with the driver
//! allow(CONSOLE_DRIVER_NUM, buffer, buffer_len_in_bytes);
//! // Initiate the transaction
//! command(CONSOLE_DRIVER_NUM, 1, len_to_write_in_bytes)
//! ```
//!
use core::cell::Cell;
use core::cmp;
use kernel::debug::debug_available_len;
use kernel::debug_process_slice;
use kernel::grant::{AllowRoCount, AllowRwCount, Grant, GrantKernelData, UpcallCount};
use kernel::hil::time::{Alarm, AlarmClient, ConvertTicks};
use kernel::hil::uart;
use kernel::processbuffer::{ReadableProcessBuffer, WriteableProcessBuffer};
use kernel::syscall::{CommandReturn, SyscallDriver};
use kernel::utilities::cells::{OptionalCell, TakeCell};
use kernel::{ErrorCode, ProcessId};
/// Syscall driver number.
use crate::driver;
pub const DRIVER_NUM: usize = driver::NUM::Console as usize;
/// Ids for read-only allow buffers
mod ro_allow {
/// Before the allow syscall was handled by the kernel,
/// console used allow number "1", so to preserve compatibility
/// we still use allow number 1 now.
pub const WRITE: usize = 1;
/// The number of read-allow buffers (for putstr) the kernel stores for this grant
pub const COUNT: u8 = 2;
}
/// Ids for read-write allow buffers
mod rw_allow {
/// Before the allow syscall was handled by the kernel,
/// console used allow number "1", so to preserve compatibility
/// we still use allow number 1 now.
pub const READ: usize = 1;
/// The number of read-write allow buffers (for getstr) the kernel stores for this grant
pub const COUNT: u8 = 2;
}
#[derive(Default)]
pub struct App {
write_position: usize, // Current write position
write_len: usize, // Length of total write
writing: bool, // Are we in the midst of a write
pending_write: bool, // Are we waiting to write
tx_counter: usize, // Used to keep order of writes
read_len: usize, // Read length
rx_counter: usize, // Used to order reads (no starvation)
}
pub struct ConsoleOrdered<'a, A: Alarm<'a>> {
uart: &'a dyn uart::Receive<'a>,
apps: Grant<
App,
UpcallCount<3>,
AllowRoCount<{ ro_allow::COUNT }>,
AllowRwCount<{ rw_allow::COUNT }>,
>,
tx_in_progress: Cell<bool>, // If true there's an ongoing write so others must wait
tx_counter: Cell<usize>, // Sequence number for writes from different processes
alarm: &'a A, // Timer for trying to send more
rx_counter: Cell<usize>,
rx_in_progress: OptionalCell<ProcessId>,
rx_buffer: TakeCell<'static, [u8]>,
atomic_size: Cell<usize>, // The maximum size write the capsule promises atomicity;
// larger writes may be broken into atomic_size chunks.
// This must be smaller than the debug buffer size or a long
// write may never print.
retry_timer: Cell<u32>, // How long the capsule will wait before retrying if there
// is insufficient space in the debug buffer (alarm ticks)
// when a write is first attempted.
write_timer: Cell<u32>, // Time to wait after a successful write into the debug buffer,
// before checking whether write more or issue a callback that
// the current write has completed (alarm ticks).
}
impl<'a, A: Alarm<'a>> ConsoleOrdered<'a, A> {
pub fn new(
uart: &'a dyn uart::Receive<'a>,
alarm: &'a A,
rx_buffer: &'static mut [u8],
grant: Grant<
App,
UpcallCount<3>,
AllowRoCount<{ ro_allow::COUNT }>,
AllowRwCount<{ rw_allow::COUNT }>,
>,
atomic_size: usize,
retry_timer: u32,
write_timer: u32,
) -> ConsoleOrdered<'a, A> {
ConsoleOrdered {
uart,
apps: grant,
tx_in_progress: Cell::new(false),
tx_counter: Cell::new(0),
alarm,
rx_counter: Cell::new(0),
rx_in_progress: OptionalCell::empty(),
rx_buffer: TakeCell::new(rx_buffer),
atomic_size: Cell::new(atomic_size),
retry_timer: Cell::new(retry_timer),
write_timer: Cell::new(write_timer),
}
}
/// Internal helper function for starting up a new print; allocate a sequence number and
/// start the send state machine.
fn send_new(
&self,
app: &mut App,
kernel_data: &GrantKernelData,
len: usize,
) -> Result<(), ErrorCode> {
// We are already writing
if app.writing || app.pending_write {
return Err(ErrorCode::BUSY);
}
app.write_position = 0;
app.write_len = kernel_data
.get_readonly_processbuffer(ro_allow::WRITE)
.map_or(0, |write| write.len())
.min(len);
// We have nothing to write
if app.write_len == 0 {
return Err(ErrorCode::NOMEM);
}
// Order the prints through a global counter.
app.tx_counter = self.tx_counter.get();
self.tx_counter.set(app.tx_counter.wrapping_add(1));
let debug_space_avail = debug_available_len();
if self.tx_in_progress.get() {
// A prior print is outstanding, enqueue
app.pending_write = true;
} else if app.write_len <= debug_space_avail {
// Space for the full write, make it
app.write_position = self.send(app, kernel_data).map_or(0, |len| len);
} else if self.atomic_size.get() <= debug_space_avail {
// Space for a partial write, make it
app.write_position = self.send(app, kernel_data).map_or(0, |len| len);
} else {
// No space even for a partial, minimum size write: enqueue
app.pending_write = true;
self.alarm.set_alarm(
self.alarm.now(),
self.alarm.ticks_from_ms(self.retry_timer.get()),
);
}
Ok(())
}
/// Internal helper function for sending data. Assumes that there is enough
/// space in the debug buffer for the write. Writes longer than available
/// debug buffer space will be truncated, so callers that wish to not lose
/// data must check before calling.
fn send(
&self,
app: &mut App,
kernel_data: &GrantKernelData,
) -> Result<usize, kernel::process::Error> {
// We can ignore the Result because if the call fails, it means
// the process has terminated, so issuing a callback doesn't matter.
// If the call fails, just use the alarm to try the next client.
let res = kernel_data
.get_readonly_processbuffer(ro_allow::WRITE)
.and_then(|write| {
write.enter(|data| {
// The slice might have become shorter than the requested
// write; if so, just write what there is.
let remaining_len = app.write_len - app.write_position;
let real_write_len = cmp::min(remaining_len, debug_available_len());
let this_write_end = app.write_position + real_write_len;
let remaining_data = match data.get(app.write_position..this_write_end) {
Some(remaining_data) => remaining_data,
None => data,
};
app.writing = true;
self.tx_in_progress.set(true);
if real_write_len > 0 {
let count = debug_process_slice!(remaining_data);
count
} else {
0
}
})
});
// Start a timer to signal completion of this write
// and potentially write more.
self.alarm.set_alarm(
self.alarm.now(),
self.alarm.ticks_from_ms(self.write_timer.get()),
);
res
}
/// Internal helper function for starting a receive operation. Processes
/// do not share reads, they take turns, with turn order monitored through
/// a sequence number.
fn receive_new(
&self,
processid: ProcessId,
app: &mut App,
kernel_data: &GrantKernelData,
len: usize,
) -> Result<(), ErrorCode> {
if app.read_len != 0 {
// We are busy reading, don't try again
Err(ErrorCode::BUSY)
} else if len == 0 {
// Cannot read length 0
Err(ErrorCode::INVAL)
} else if self.rx_buffer.is_none() {
// Console is busy receiving, so enqueue
app.rx_counter = self.rx_counter.get();
self.rx_counter.set(app.rx_counter + 1);
app.read_len = len;
Ok(())
} else {
// App can try to start a read
let read_len = kernel_data
.get_readwrite_processbuffer(rw_allow::READ)
.map_or(0, |read| read.len())
.min(len);
if read_len > self.rx_buffer.map_or(0, |buf| buf.len()) {
// For simplicity, impose a small maximum receive length
// instead of doing incremental reads
Err(ErrorCode::INVAL)
} else {
// Note: We have ensured above that rx_buffer is present
app.read_len = read_len;
self.rx_buffer.take().map(|buffer| {
self.rx_in_progress.set(processid);
let _ = self.uart.receive_buffer(buffer, app.read_len);
});
Ok(())
}
}
}
}
impl<'a, A: Alarm<'a>> AlarmClient for ConsoleOrdered<'a, A> {
fn alarm(&self) {
if self.tx_in_progress.get() {
// Clear here and set it later; if .enter fails (process
// has died) it remains cleared.
self.tx_in_progress.set(false);
// Check if the current writer is finished; if so, issue an upcall, if not,
// try to write more.
for cntr in self.apps.iter() {
cntr.enter(|app, kernel_data| {
// This is the in-progress write
if app.writing {
if app.write_position >= app.write_len {
let _res = kernel_data.schedule_upcall(1, (app.write_len, 0, 0));
app.writing = false;
} else {
// Still have more to write, don't allow others to jump in.
self.tx_in_progress.set(true);
// Promise to write to the end, or the atomic write unit, whichever is smaller
let remaining_len = app.write_len - app.write_position;
let debug_space_avail = debug_available_len();
let minimum_write = cmp::min(remaining_len, self.atomic_size.get());
// Write, or if there isn't space for a minimum write, retry later
if minimum_write <= debug_space_avail {
app.write_position +=
self.send(app, kernel_data).map_or(0, |len| len);
} else {
self.alarm.set_alarm(
self.alarm.now(),
self.alarm.ticks_from_ms(self.retry_timer.get()),
);
}
}
}
});
}
}
// There's no ongoing send, try to send the next one (process with
// lowest sequence number).
if !self.tx_in_progress.get() {
// Find if there's another writer and mark it busy.
let mut next_writer: Option<ProcessId> = None;
let mut seqno = self.tx_counter.get();
// Find the process that has an outstanding write with the
// earliest sequence number, handling wraparound.
for cntr in self.apps.iter() {
let appid = cntr.processid();
cntr.enter(|app, _| {
if app.pending_write {
// Checks wither app.tx_counter is earlier than
// seqno, with the constrain that there are <
// usize/2 processes. wrapping_sub allows this to
// handle wraparound E.g., in 8-bit arithmetic
// 0x02 - 0xff = 0x03 and so 0xff is "earlier"
// than 0x02. -pal
if seqno.wrapping_sub(app.tx_counter) < usize::MAX / 2 {
seqno = app.tx_counter;
next_writer = Some(appid);
}
}
});
}
next_writer.map(|pid| {
self.apps.enter(pid, |app, kernel_data| {
app.pending_write = false;
let len = app.write_len;
let _ = self.send_new(app, kernel_data, len);
})
});
}
}
}
impl<'a, A: Alarm<'a>> SyscallDriver for ConsoleOrdered<'a, A> {
/// Setup shared buffers.
///
/// ### `allow_num`
///
/// - `0`: Readonly buffer for write buffer
// Setup callbacks.
//
// ### `subscribe_num`
//
// - `1`: Write buffer completed callback
/// Initiate serial transfers
///
/// ### `command_num`
///
/// - `0`: Driver existence check.
/// - `1`: Transmits a buffer passed via `allow`, up to the length
/// passed in `arg1`
fn command(&self, cmd_num: usize, arg1: usize, _: usize, appid: ProcessId) -> CommandReturn {
let res = self
.apps
.enter(appid, |app, kernel_data| {
match cmd_num {
0 => Ok(()),
1 => {
// putstr
let len = arg1;
self.send_new(app, kernel_data, len)
}
2 => {
// getnstr
let len = arg1;
self.receive_new(appid, app, kernel_data, len)
}
3 => {
// Abort RX
let _ = self.uart.receive_abort();
Ok(())
}
_ => Err(ErrorCode::NOSUPPORT),
}
})
.map_err(ErrorCode::from);
match res {
Ok(Ok(())) => CommandReturn::success(),
Ok(Err(e)) => CommandReturn::failure(e),
Err(e) => CommandReturn::failure(e),
}
}
fn allocate_grant(&self, processid: ProcessId) -> Result<(), kernel::process::Error> {
self.apps.enter(processid, |_, _| {})
}
}
impl<'a, A: Alarm<'a>> uart::ReceiveClient for ConsoleOrdered<'a, A> {
fn received_buffer(
&self,
buffer: &'static mut [u8],
rx_len: usize,
rcode: Result<(), ErrorCode>,
error: uart::Error,
) {
// First, handle this read, then see if there's another read to process.
self.rx_in_progress
.take()
.map(|processid| {
self.apps
.enter(processid, |app, kernel_data| {
// An iterator over the returned buffer yielding only the first `rx_len`
// bytes
let rx_buffer = buffer.iter().take(rx_len);
app.read_len = 0; // Mark that we are no longer reading.
match error {
uart::Error::None | uart::Error::Aborted => {
// Receive some bytes, signal error type and return bytes to process buffer
let count = kernel_data
.get_readwrite_processbuffer(rw_allow::READ)
.and_then(|read| {
read.mut_enter(|data| {
let mut c = 0;
for (a, b) in data.iter().zip(rx_buffer) {
c += 1;
a.set(*b);
}
c
})
})
.unwrap_or(-1);
// Make sure we report the same number
// of bytes that we actually copied into
// the app's buffer. This is defensive:
// we shouldn't ever receive more bytes
// than will fit in the app buffer since
// we use the app_buffer's length when
// calling `receive()`. However, a buggy
// lower layer could return more bytes
// than we asked for, and we don't want
// to propagate that length error to
// userspace. However, we do return an
// error code so that userspace knows
// something went wrong.
//
// If count < 0 this means the buffer
// disappeared: return NOMEM.
let read_buffer_len = kernel_data
.get_readwrite_processbuffer(rw_allow::READ)
.map_or(0, |read| read.len());
let (ret, received_length) = if count < 0 {
(Err(ErrorCode::NOMEM), 0)
} else if rx_len > read_buffer_len {
// Return `SIZE` indicating that
// some received bytes were dropped.
// We report the length that we
// actually copied into the buffer,
// but also indicate that there was
// an issue in the kernel with the
// receive.
(Err(ErrorCode::SIZE), read_buffer_len)
} else {
// This is the normal and expected
// case.
(rcode, rx_len)
};
kernel_data
.schedule_upcall(
2,
(
kernel::errorcode::into_statuscode(ret),
received_length,
0,
),
)
.ok();
}
_ => {
// Some UART error occurred
kernel_data
.schedule_upcall(
2,
(
kernel::errorcode::into_statuscode(Err(
ErrorCode::FAIL,
)),
0,
0,
),
)
.ok();
}
}
})
.unwrap_or_default();
})
.unwrap_or_default();
// Whatever happens, we want to make sure to replace the rx_buffer for future transactions
self.rx_buffer.replace(buffer);
// Find if there's another reader and if so start reading
let mut next_reader: Option<ProcessId> = None;
let mut seqno = self.tx_counter.get();
for cntr in self.apps.iter() {
let appid = cntr.processid();
cntr.enter(|app, _| {
if app.read_len != 0 {
// Checks wither app.tx_counter is earlier than
// seqno, with the constrain that there are <
// usize/2 processes. wrapping_sub allows this to
// handle wraparound E.g., in 8-bit arithmetic
// 0x02 - 0xff = 0x03 and so 0xff is "earlier"
// than 0x02. -pal
if seqno.wrapping_sub(app.rx_counter) < usize::MAX / 2 {
seqno = app.rx_counter;
next_reader = Some(appid);
}
}
});
}
next_reader.map(|pid| {
self.apps.enter(pid, |app, kernel_data| {
let len = app.read_len;
let _ = self.receive_new(pid, app, kernel_data, len);
})
});
}
}