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Use shared references for MemReader methods #157

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gabrielesvelto merged 1 commit into from
Sep 26, 2025
Merged

Use shared references for MemReader methods #157

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42 changes: 25 additions & 17 deletions src/linux/mem_reader.rs
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Original file line number Diff line number Diff line change
@@ -1,7 +1,11 @@
//! Functionality for reading a remote process's memory

use super::{minidump_writer::MinidumpWriter, serializers::*, Pid};
use {
super::{minidump_writer::MinidumpWriter, serializers::*, Pid},
std::sync::OnceLock,
};

#[derive(Debug)]
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@gabrielesvelto gabrielesvelto Sep 22, 2025

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Is the Debug trait required or can it be removed? I wouldn't add it unless the structure is user-printable.

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@marti4d marti4d Sep 26, 2025 •
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Yep -- This is needed to be able to use Result::expect() on the potential Err(Style) that might be returned by OnceLock::set(). Alternatively, I could use .ok().expect(...) on it to avoid this, but honestly this is an internal type anyway - What's the point of avoiding #[derive(Debug)] on it?

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@gabrielesvelto gabrielesvelto Sep 26, 2025

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Ah, I see, thanks!

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@gabrielesvelto gabrielesvelto Sep 26, 2025

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It was just to avoid unnecessary codegen.

enum Style {
/// Uses [`process_vm_readv`](https://linux.die.net/man/2/process_vm_readv)
/// to read the memory.
Expand Down Expand Up @@ -42,12 +46,12 @@ pub struct CopyFromProcessError {
pub struct MemReader {
/// The pid of the child to read
pid: nix::unistd::Pid,
style: Option<Style>,
style: OnceLock<Style>,
}

impl std::fmt::Debug for MemReader {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
let s = match &self.style {
let s = match self.style.get() {
Some(Style::VirtualMem) => "process_vm_readv",
Some(Style::File(_)) => "/proc/<pid>/mem",
Some(Style::Ptrace) => "PTRACE_PEEKDATA",
Expand All @@ -71,7 +75,7 @@ impl MemReader {
pub fn new(pid: i32) -> Self {
Self {
pid: nix::unistd::Pid::from_raw(pid),
style: None,
style: OnceLock::default(),
}
}

Expand All @@ -80,7 +84,7 @@ impl MemReader {
pub fn for_virtual_mem(pid: i32) -> Self {
Self {
pid: nix::unistd::Pid::from_raw(pid),
style: Some(Style::VirtualMem),
style: OnceLock::from(Style::VirtualMem),
}
}

Expand All @@ -91,7 +95,7 @@ impl MemReader {

Ok(Self {
pid: nix::unistd::Pid::from_raw(pid),
style: Some(Style::File(file)),
style: OnceLock::from(Style::File(file)),
})
}

Expand All @@ -100,13 +104,13 @@ impl MemReader {
pub fn for_ptrace(pid: i32) -> Self {
Self {
pid: nix::unistd::Pid::from_raw(pid),
style: Some(Style::Ptrace),
style: OnceLock::from(Style::Ptrace),
}
}

#[inline]
pub fn read_to_vec(
&mut self,
&self,
src: usize,
length: std::num::NonZeroUsize,
) -> Result<Vec<u8>, CopyFromProcessError> {
Expand All @@ -116,8 +120,8 @@ impl MemReader {
Ok(output)
}

pub fn read(&mut self, src: usize, dst: &mut [u8]) -> Result<usize, CopyFromProcessError> {
if let Some(rs) = &mut self.style {
pub fn read(&self, src: usize, dst: &mut [u8]) -> Result<usize, CopyFromProcessError> {
if let Some(rs) = self.style.get() {
let res = match rs {
Style::VirtualMem => Self::vmem(self.pid, src, dst).map_err(|s| (s, 0)),
Style::File(file) => Self::file(file, src, dst).map_err(|s| (s, 0)),
Expand All @@ -134,19 +138,21 @@ impl MemReader {
});
}

const DOUBLE_INIT_MSG: &str = "somehow MemReader initialized twice";

// Attempt to read in order of speed
let vmem = match Self::vmem(self.pid, src, dst) {
Ok(len) => {
self.style = Some(Style::VirtualMem);
self.style.set(Style::VirtualMem).expect(DOUBLE_INIT_MSG);
return Ok(len);
}
Err(err) => err,
};

let file = match std::fs::File::open(format!("/proc/{}/mem", self.pid)) {
Ok(mut file) => match Self::file(&mut file, src, dst) {
Ok(file) => match Self::file(&file, src, dst) {
Ok(len) => {
self.style = Some(Style::File(file));
self.style.set(Style::File(file)).expect(DOUBLE_INIT_MSG);
return Ok(len);
}
Err(err) => err,
Expand All @@ -158,13 +164,15 @@ impl MemReader {

let ptrace = match Self::ptrace(self.pid, src, dst) {
Ok(len) => {
self.style = Some(Style::Ptrace);
self.style.set(Style::Ptrace).expect(DOUBLE_INIT_MSG);
return Ok(len);
}
Err((err, _)) => err,
};

self.style = Some(Style::Unavailable { vmem, file, ptrace });
self.style
.set(Style::Unavailable { vmem, file, ptrace })
.expect(DOUBLE_INIT_MSG);
Err(CopyFromProcessError {
child: self.pid.as_raw(),
src,
Expand All @@ -184,7 +192,7 @@ impl MemReader {
}

#[inline]
fn file(file: &mut std::fs::File, src: usize, dst: &mut [u8]) -> Result<usize, nix::Error> {
fn file(file: &std::fs::File, src: usize, dst: &mut [u8]) -> Result<usize, nix::Error> {
use std::os::unix::fs::FileExt;

file.read_exact_at(dst, src as u64).map_err(|err| {
Expand Down Expand Up @@ -246,7 +254,7 @@ impl MinidumpWriter {
source: nix::errno::Errno::EINVAL,
})?;

let mut mem = MemReader::new(pid);
let mem = MemReader::new(pid);
mem.read_to_vec(src, length)
}
}
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