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Support BufferSegments in linux kernel #422

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Support BufferSegments in linux kernel #422

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5364e12
Adapt BufferSegments for usage in the linux kernel
ariel-miculas Jul 4, 2023
b5b94b1
Return an error when trying to display floating point values in the l…
ariel-miculas Jul 4, 2023
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13 changes: 13 additions & 0 deletions capnp/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -32,6 +32,8 @@
#[cfg(feature = "alloc")]
#[macro_use]
extern crate alloc;
#[cfg(feature = "kernel")]
extern crate alloc;

/// Code generated from
/// [schema.capnp](https://github.com/capnproto/capnproto/blob/master/c%2B%2B/src/capnp/schema.capnp).
Expand Down Expand Up @@ -358,6 +360,9 @@ pub enum ErrorKind {
/// Only one of the section pointers is pointing to ourself
OnlyOneOfTheSectionPointersIsPointingToOurself,

/// Out of memory
OutOfMemory,

/// Packed input did not end cleanly on a segment boundary.
PackedInputDidNotEndCleanlyOnASegmentBoundary,

Expand Down Expand Up @@ -489,6 +494,13 @@ impl core::convert::From<NotInSchema> for Error {
}
}

#[cfg(any(feature = "alloc", feature = "kernel"))]
impl core::convert::From<alloc::collections::TryReserveError> for Error {
fn from(_err: alloc::collections::TryReserveError) -> Self {
Self::from_kind(ErrorKind::OutOfMemory)
}
}

impl core::fmt::Display for ErrorKind {
fn fmt(&self, fmt: &mut core::fmt::Formatter) -> core::result::Result<(), core::fmt::Error> {
match self {
Expand Down Expand Up @@ -548,6 +560,7 @@ impl core::fmt::Display for ErrorKind {
Self::NestingLimitExceeded => write!(fmt, "nesting limit exceeded"),
Self::NotAStruct => write!(fmt, "not a struct"),
Self::OnlyOneOfTheSectionPointersIsPointingToOurself => write!(fmt, "Only one of the section pointers is pointing to ourself"),
Self::OutOfMemory => write!(fmt, "Out of memory"),
Self::PackedInputDidNotEndCleanlyOnASegmentBoundary => write!(fmt, "Packed input did not end cleanly on a segment boundary."),
Self::PrematureEndOfFile => write!(fmt, "Premature end of file"),
Self::PrematureEndOfPackedInput => write!(fmt, "Premature end of packed input."),
Expand Down
65 changes: 54 additions & 11 deletions capnp/src/serialize.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -26,20 +26,22 @@
mod no_alloc_slice_segments;
pub use no_alloc_slice_segments::NoAllocSliceSegments;

#[cfg(any(feature = "alloc", feature = "kernel"))]
use crate::io::Read;
#[cfg(feature = "alloc")]
use crate::io::{Read, Write};
#[cfg(feature = "alloc")]
use crate::io::Write;
#[cfg(any(feature = "alloc", feature = "kernel"))]
use alloc::vec::Vec;
#[cfg(feature = "alloc")]
use core::convert::TryInto;
#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
use core::ops::Deref;

use crate::message;
#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
use crate::private::units::BYTES_PER_WORD;
use crate::Result;
#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
use crate::{Error, ErrorKind};

pub const SEGMENTS_COUNT_LIMIT: usize = 512;
Expand Down Expand Up @@ -124,7 +126,7 @@ pub fn read_message_from_flat_slice_no_alloc<'a>(

/// Segments read from a buffer, useful for when you have the message in a buffer and don't want the extra
/// copy of `read_message`.
#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
pub struct BufferSegments<T> {
buffer: T,

Expand All @@ -136,7 +138,7 @@ pub struct BufferSegments<T> {
segment_indices: Vec<(usize, usize)>,
}

#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
impl<T: Deref<Target = [u8]>> BufferSegments<T> {
/// Reads a serialized message (including a segment table) from a buffer and takes ownership, without copying.
/// The buffer is allowed to be longer than the message. Provide this to `Reader::new` with options that make
Expand Down Expand Up @@ -166,7 +168,7 @@ impl<T: Deref<Target = [u8]>> BufferSegments<T> {
}
}

#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
impl<T: Deref<Target = [u8]>> message::ReaderSegments for BufferSegments<T> {
fn get_segment(&self, id: u32) -> Option<&[u8]> {
if id < self.segment_indices.len() as u32 {
Expand Down Expand Up @@ -227,35 +229,57 @@ impl crate::message::ReaderSegments for OwnedSegments {
}
}

#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
/// Helper object for constructing an `OwnedSegments` or a `SliceSegments`.
pub struct SegmentLengthsBuilder {
segment_indices: Vec<(usize, usize)>,
total_words: usize,
}

#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
impl SegmentLengthsBuilder {
/// Creates a new `SegmentsLengthsBuilder`, initializing the segment_indices vector with
/// `Vec::with_capacitiy(capacity)`. `capacity` should equal the number of times that `push_segment()`
/// is expected to be called.
#[cfg(feature = "alloc")]
pub fn with_capacity(capacity: usize) -> Self {
Self {
segment_indices: Vec::with_capacity(capacity),
total_words: 0,
}
}
/// Creates a new `SegmentsLengthsBuilder`, initializing the segment_indices vector with
/// `Vec::with_capacitiy(capacity)`. `capacity` should equal the number of times that `push_segment()`
/// is expected to be called.
#[cfg(feature = "kernel")]
pub fn with_capacity(capacity: usize) -> Result<Self> {
Ok(Self {
segment_indices: Vec::try_with_capacity(capacity)?,
total_words: 0,
})
}

#[cfg(feature = "alloc")]
/// Pushes a new segment length. The `n`th time (starting at 0) this is called specifies the length of
/// the segment with ID `n`.
pub fn push_segment(&mut self, length_in_words: usize) {
self.segment_indices
.push((self.total_words, self.total_words + length_in_words));
self.total_words += length_in_words;
}
#[cfg(feature = "kernel")]
/// Pushes a new segment length. The `n`th time (starting at 0) this is called specifies the length of
/// the segment with ID `n`.
pub fn push_segment(&mut self, length_in_words: usize) -> Result<()> {
self.segment_indices
.try_push((self.total_words, self.total_words + length_in_words))?;
self.total_words += length_in_words;
Ok(())
}

/// Constructs an `OwnedSegments`, allocating a single buffer of 8-byte aligned memory to hold
/// all segments.
#[cfg(feature = "alloc")]
pub fn into_owned_segments(self) -> OwnedSegments {
let owned_space = crate::Word::allocate_zeroed_vec(self.total_words);
OwnedSegments {
Expand All @@ -265,6 +289,7 @@ impl SegmentLengthsBuilder {
}

/// Constructs a `SliceSegments`, where the passed-in slice is assumed to contain the segments.
#[cfg(feature = "alloc")]
pub fn into_slice_segments(self, slice: &[u8]) -> SliceSegments {
assert!(self.total_words * BYTES_PER_WORD <= slice.len());
SliceSegments {
Expand Down Expand Up @@ -332,7 +357,7 @@ where
///
/// The segment table format for streams is defined in the Cap'n Proto
/// [encoding spec](https://capnproto.org/encoding.html)
#[cfg(feature = "alloc")]
#[cfg(any(feature = "alloc", feature = "kernel"))]
fn read_segment_table<R>(
read: &mut R,
options: message::ReaderOptions,
Expand Down Expand Up @@ -364,25 +389,43 @@ where
)));
}

#[cfg(feature = "alloc")]
let mut segment_lengths_builder = SegmentLengthsBuilder::with_capacity(segment_count);
#[cfg(feature = "kernel")]
let mut segment_lengths_builder = SegmentLengthsBuilder::with_capacity(segment_count)?;
#[cfg(feature = "alloc")]
segment_lengths_builder
.push_segment(u32::from_le_bytes(buf[4..8].try_into().unwrap()) as usize);
#[cfg(feature = "kernel")]
segment_lengths_builder
.push_segment(u32::from_le_bytes(buf[4..8].try_into().unwrap()) as usize)?;
if segment_count > 1 {
if segment_count < 4 {
read.read_exact(&mut buf)?;
for idx in 0..(segment_count - 1) {
let segment_len =
u32::from_le_bytes(buf[(idx * 4)..(idx + 1) * 4].try_into().unwrap()) as usize;
#[cfg(feature = "alloc")]
segment_lengths_builder.push_segment(segment_len);
#[cfg(feature = "kernel")]
segment_lengths_builder.push_segment(segment_len)?;
}
} else {
#[cfg(feature = "alloc")]
let mut segment_sizes = vec![0u8; (segment_count & !1) * 4];
#[cfg(feature = "kernel")]
let mut segment_sizes = Vec::try_with_capacity((segment_count & !1) * 4)?;
#[cfg(feature = "kernel")]
segment_sizes.try_resize((segment_count & !1) * 4, 0)?;
read.read_exact(&mut segment_sizes[..])?;
for idx in 0..(segment_count - 1) {
let segment_len =
u32::from_le_bytes(segment_sizes[(idx * 4)..(idx + 1) * 4].try_into().unwrap())
as usize;
#[cfg(feature = "alloc")]
segment_lengths_builder.push_segment(segment_len);
#[cfg(feature = "kernel")]
segment_lengths_builder.push_segment(segment_len)?;
}
}
}
Expand Down
4 changes: 4 additions & 0 deletions capnp/src/stringify.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -69,8 +69,12 @@ pub(crate) fn print(
dynamic_value::Reader::UInt16(x) => formatter.write_fmt(format_args!("{x}")),
dynamic_value::Reader::UInt32(x) => formatter.write_fmt(format_args!("{x}")),
dynamic_value::Reader::UInt64(x) => formatter.write_fmt(format_args!("{x}")),
#[cfg(not(feature = "kernel"))]
dynamic_value::Reader::Float32(x) => formatter.write_fmt(format_args!("{x}")),
#[cfg(not(feature = "kernel"))]
dynamic_value::Reader::Float64(x) => formatter.write_fmt(format_args!("{x}")),
#[cfg(feature = "kernel")]
dynamic_value::Reader::Float32(_) | dynamic_value::Reader::Float64(_) => Err(fmt::Error),
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@dwrensha dwrensha Jul 4, 2023 •
edited
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So when compiling for the Linux kernel, format_args!("{x}") is a compile-time error when x is a floating point number? Is that true for format_args!("{x:?}") as well?

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For your first question, yes:

error[E0277]: `f32` doesn't implement `Display`
  --> rust/capnp/stringify.rs:74:81
   |
74 |         dynamic_value::Reader::Float32(x) => formatter.write_fmt(format_args!("{x}")),
   |                                                                                 ^ `f32` cannot be formatted with the default formatter
   |
   = help: the trait `Display` is not implemented for `f32`
   = note: in format strings you may be able to use `{:?}` (or {:#?} for pretty-print) instead
   = help: the following other types implement trait `Display`:
             i128
             i16
             i32
             i64
             i8
             isize
             u128
             u16
           and 4 others
   = note: this error originates in the macro `format_args` (in Nightly builds, run with -Z macro-backtrace for more info)

error: aborting due to previous error

However, I was surprised to see it is not a compile time error for format_args!("{x:?}"). I will need to test what happens in that case.

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Trying to display a float using the debug formatting leads to a kernel panic:

        let x:f32 = 4.2;
        pr_info!("trying to display float");
        pr_info!("{}", format_args!("{x:?}"));


~ # mount -t puzzlefs none /mnt
[   10.747124] puzzlefs: trying to display float
[   10.747132] rust_kernel: panicked at 'floating point support is turned off', /home/amiculas/.rustup/toolchains/1.68.2-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/library/core/src/fmt/1
[   10.750707] ------------[ cut here ]------------
[   10.751557] kernel BUG at rust/helpers.c:34!
[   10.752269] invalid opcode: 0000 [#1] SMP
[   10.752892] CPU: 0 PID: 49 Comm: mount Not tainted 6.4.0-rc4+ #330
[   10.753791] Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS Arch Linux 1.16.2-1-1 04/01/2014
[   10.755058] RIP: 0010:rust_helper_BUG+0x8/0x10
[   10.755683] Code: 00 00 48 8d 7d d0 48 c7 c6 a0 da 82 81 e8 a0 20 2d 00 0f 0b cc cc cc cc cc cc cc cc cc cc cc cc cc cc f3 0f 1e fa 55 48 89 e5 <0f> 0b 66 0f 1f 44 00 00 f3 0f 1e fa 55 d
[   10.758422] RSP: 0018:ffffc90000107620 EFLAGS: 00010092
[   10.759250] RAX: 00000000000000bc RBX: ffffc90000107d30 RCX: ffffffff81a35ff0
[   10.760201] RDX: 0000000000000002 RSI: c0000000ffffefff RDI: 0000000000002ffd
[   10.760929] RBP: ffffc90000107620 R08: 0000000000000000 R09: ffffffff81a4e280
[   10.761654] R10: 00000000ffffefff R11: 0000000000000000 R12: 0000000000000000
[   10.762390] R13: 0000000000000010 R14: ffffffff8185ed30 R15: 0000000000000000
[   10.763128] FS:  0000000000f353c0(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000
[   10.763979] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   10.764589] CR2: 0000000000641fc0 CR3: 0000000100e8c002 CR4: 0000000000770eb0
[   10.765158] PKRU: 55555554
[   10.765341] Call Trace:
[   10.765504]  <TASK>
[   10.765645]  ? __die_body+0x62/0xb0
[   10.765874]  ? die+0x8c/0xb0
[   10.766065]  ? do_trap+0x87/0x150
[   10.766282]  ? rust_helper_BUG+0x8/0x10
[   10.766530]  ? handle_invalid_op+0x68/0x80
[   10.766794]  ? rust_helper_BUG+0x8/0x10
[   10.767041]  ? exc_invalid_op+0x36/0x50
[   10.767288]  ? asm_exc_invalid_op+0x1f/0x30
[   10.767559]  ? rust_helper_BUG+0x8/0x10
[   10.767806]  rust_begin_unwind+0x62/0x80
[   10.768059]  ? mas_replace+0x2b4/0x350
[   10.768302]  ? _RNvXsX_NtCsjQkEVdlX3YU_4core3fmtRNtNtCscRhiiH9rU7O_6kernel3str4CStrNtB5_7Display3fmtBz_+0xc0/0xc0
[   10.768981]  _RNvNtCsjQkEVdlX3YU_4core9panicking9panic_fmt+0x2d/0x30
[   10.769490]  _RNvXNtNtCsjQkEVdlX3YU_4core3fmt7nofloatfNtB4_5Debug3fmt+0x40/0x50
[   10.769981]  ? call_rcu+0xd4/0x220
[   10.770165]  _RNvNtCsjQkEVdlX3YU_4core3fmt5write+0x1ba/0x220
[   10.770389]  _RNvXs5_NtCsjQkEVdlX3YU_4core3fmtNtB5_9ArgumentsNtB5_7Display3fmt+0x4a/0x50
[   10.770703]  ? _RINvNtCsjQkEVdlX3YU_4core3ptr13drop_in_placeINtNtNtCscRhiiH9rU7O_6kernel2fs5param15ConcreteHandleruNCINvNtBJ_3s327handleruE0EECshR6aa2uJhw8_8puzzlefs+0x10/0x10
[   10.771303]  _RNvNtCsjQkEVdlX3YU_4core3fmt5write+0x1ba/0x220
[   10.771527]  rust_fmt_argument+0x5f/0x70
[   10.771683]  ? _RINvNtCsjQkEVdlX3YU_4core3ptr13drop_in_placeINtNtNtCscRhiiH9rU7O_6kernel2fs5param15ConcreteHandleruNCINvNtBJ_3s327handleruE0EECshR6aa2uJhw8_8puzzlefs+0x10/0x10
[   10.772286]  pointer+0x4c6/0x6a0
[   10.772418]  vsnprintf+0x493/0x730
[   10.772557]  vprintk_store+0x194/0x5a0
[   10.772708]  ? console_unlock+0xe1/0x100
[   10.772865]  vprintk_emit+0x65/0x1c0
[   10.773009]  vprintk_default+0x1c/0x20
[   10.773159]  vprintk+0x4d/0x60
[   10.773284]  _printk+0x4a/0x50
[   10.773408]  _RNvXCshR6aa2uJhw8_8puzzlefsNtB2_8PuzzleFsNtNtCscRhiiH9rU7O_6kernel2fs4Type10fill_super+0x50b/0x520
[   10.773801]  ? _RINvNtCsjQkEVdlX3YU_4core3ptr13drop_in_placeINtNtNtCscRhiiH9rU7O_6kernel2fs5param15ConcreteHandleruNCINvNtBJ_3s327handleruE0EECshR6aa2uJhw8_8puzzlefs+0x10/0x10
[   10.774399]  ? _RINvNtCsjQkEVdlX3YU_4core3ptr13drop_in_placeINtNtNtCscRhiiH9rU7O_6kernel2fs5param15ConcreteHandleruNCINvNtBJ_3s327handleruE0EECshR6aa2uJhw8_8puzzlefs+0x10/0x10
[   10.774997]  ? _RINvNtCsjQkEVdlX3YU_4core3ptr13drop_in_placeINtNtNtCscRhiiH9rU7O_6kernel2fs5param15ConcreteHandleruNCINvNtBJ_3s327handleruE0EECshR6aa2uJhw8_8puzzlefs+0x10/0x10
[   10.775598]  ? _RINvNtCsjQkEVdlX3YU_4core3ptr13drop_in_placeINtNtNtCscRhiiH9rU7O_6kernel2fs5param15ConcreteHandleruNCINvNtBJ_3s327handleruE0EECshR6aa2uJhw8_8puzzlefs+0x10/0x10
[   10.776195]  ? _RNvXs4_NtCsjQkEVdlX3YU_4core3fmtNtB5_9ArgumentsNtB5_5Debug3fmt+0x50/0x50
[   10.776508]  ? _RNvXs13_NtNtCsjQkEVdlX3YU_4core4sync6atomicNtB6_11AtomicUsizeNtNtBa_3fmt5Debug3fmt+0x20/0x20
[   10.776888]  ? _RNvMNtCscRhiiH9rU7O_6kernel2fsINtB2_6TablesNtCshR6aa2uJhw8_8puzzlefs8PuzzleFsE17get_tree_callbackBH_+0x20/0x20
[   10.777325]  _RNvMNtCscRhiiH9rU7O_6kernel2fsINtB2_6TablesNtCshR6aa2uJhw8_8puzzlefs8PuzzleFsE19fill_super_callbackBH_+0x29/0x50
[   10.777763]  ? _RNvMNtCscRhiiH9rU7O_6kernel2fsINtB2_6TablesNtCshR6aa2uJhw8_8puzzlefs8PuzzleFsE17get_tree_callbackBH_+0x20/0x20
[   10.778199]  vfs_get_super+0x8c/0x120
[   10.778346]  get_tree_nodev+0x14/0x20
[   10.778492]  vfs_get_tree+0x20/0x90
[   10.778635]  do_new_mount+0x140/0x340
[   10.778784]  path_mount+0x384/0x620
[   10.778924]  __x64_sys_mount+0x142/0x1a0
[   10.779081]  do_syscall_64+0x48/0x90
[   10.779224]  entry_SYSCALL_64_after_hwframe+0x46/0xb0
[   10.779423] RIP: 0033:0x4958ce
[   10.779547] Code: 48 c7 c1 e0 ff ff ff f7 d8 64 89 01 48 83 c8 ff c3 66 2e 0f 1f 84 00 00 00 00 00 90 f3 0f 1e fa 49 89 ca b8 a5 00 00 00 0f 05 <48> 3d 01 f0 ff ff 73 01 c3 48 c7 c1 e0 8
[   10.780314] RSP: 002b:00007ffcabbf9228 EFLAGS: 00000246 ORIG_RAX: 00000000000000a5
[   10.780608] RAX: ffffffffffffffda RBX: 00007ffcabbf93f8 RCX: 00000000004958ce
[   10.780886] RDX: 00007ffcabbf9fba RSI: 00007ffcabbf9fc8 RDI: 00007ffcabbf9fc3
[   10.781163] RBP: 00007ffcabbf9fc3 R08: 0000000000000000 R09: 0000000000000000
[   10.781440] R10: 0000000000008000 R11: 0000000000000246 R12: 00007ffcabbf9fc8
[   10.781717] R13: 00007ffcabbf9fba R14: 0000000000008000 R15: 00007ffcabbf9720
[   10.782007]  </TASK>
[   10.782097] Modules linked in:
[   10.782222] ---[ end trace 0000000000000000 ]---
[   10.782404] RIP: 0010:rust_helper_BUG+0x8/0x10
[   10.782581] Code: 00 00 48 8d 7d d0 48 c7 c6 a0 da 82 81 e8 a0 20 2d 00 0f 0b cc cc cc cc cc cc cc cc cc cc cc cc cc cc f3 0f 1e fa 55 48 89 e5 <0f> 0b 66 0f 1f 44 00 00 f3 0f 1e fa 55 d
[   10.783295] RSP: 0018:ffffc90000107620 EFLAGS: 00010092
[   10.783499] RAX: 00000000000000bc RBX: ffffc90000107d30 RCX: ffffffff81a35ff0
[   10.783775] RDX: 0000000000000002 RSI: c0000000ffffefff RDI: 0000000000002ffd
[   10.784053] RBP: ffffc90000107620 R08: 0000000000000000 R09: ffffffff81a4e280
[   10.784331] R10: 00000000ffffefff R11: 0000000000000000 R12: 0000000000000000
[   10.784609] R13: 0000000000000010 R14: ffffffff8185ed30 R15: 0000000000000000
[   10.784886] FS:  0000000000f353c0(0000) GS:ffff88813bc00000(0000) knlGS:0000000000000000
[   10.785198] CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
[   10.785425] CR2: 0000000000641fc0 CR3: 0000000100e8c002 CR4: 0000000000770eb0
[   10.785703] PKRU: 55555554
[   10.785812] note: mount[49] exited with irqs disabled
Segmentation fault

dynamic_value::Reader::Enum(e) => match cvt(e.get_enumerant())? {
Some(enumerant) => formatter.write_str(cvt(enumerant.get_proto().get_name())?),
None => formatter.write_fmt(format_args!("{}", e.get_value())),
Expand Down
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