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Optimize `copy_to_user`

This commit is contained in:
Ruihan Li 2026-01-03 12:21:08 +08:00
parent 003d8efa24
commit 4ec3aef4f2
1 changed files with 43 additions and 78 deletions
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121
kernel/src/fs/notify/inotify.rs
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@ -10,6 +10,7 @@ use core::{
sync::atomic::{AtomicBool, AtomicU32, AtomicU64, Ordering},
};
use align_ext::AlignExt;
use bitflags::bitflags;
use hashbrown::HashMap;
use ostd::{mm::VmWriter, sync::SpinLock};
@ -254,16 +255,11 @@ impl InotifyFile {
fn get_all_event_size(&self) -> usize {
let event_queue = self.event_queue.lock();
event_queue.iter().map(|event| event.get_size()).sum()
event_queue.iter().map(|event| event.total_size()).sum()
}
/// Tries to read events from the notification queue.
fn try_read(&self, writer: &mut VmWriter) -> Result<usize> {
const HEADER_SIZE: usize = size_of::<InotifyEventHeader>();
if writer.avail() < HEADER_SIZE {
return_errno_with_message!(Errno::EINVAL, "buffer is too small");
}
// This ensures that we report continuous events even when the user program attempts to
// call `read()` concurrently.
let _guard = self.read_mutex.lock();
@ -412,13 +408,13 @@ impl FileLike for InotifyFile {
}
/// Checks if the event type is mergeable.
fn is_mergeable_event_type(event: FsEvents) -> bool {
event & (FsEvents::MODIFY | FsEvents::ATTRIB | FsEvents::ACCESS) != FsEvents::empty()
fn is_mergeable_event_type(event: u32) -> bool {
event & (FsEvents::MODIFY | FsEvents::ATTRIB | FsEvents::ACCESS).bits() != 0
}
/// Checks if two inotify events can be merged.
fn can_merge_events(existing: &InotifyEvent, new_event: &InotifyEvent) -> bool {
existing.wd() == new_event.wd()
existing.header.wd == new_event.header.wd
&& existing.name == new_event.name
&& existing.header.event == new_event.header.event
&& is_mergeable_event_type(new_event.header.event)
@ -536,95 +532,64 @@ struct InotifyEvent {
///
/// Reference: <https://elixir.bootlin.com/linux/v6.17.8/source/include/uapi/linux/inotify.h#L21>
#[repr(C)]
#[derive(Clone, Copy, Pod)]
struct InotifyEventHeader {
wd: u32,
event: FsEvents,
event: u32,
cookie: u32,
name_len: u32,
}
impl InotifyEvent {
fn new(wd: u32, event: FsEvents, cookie: u32, name: Option<String>) -> Self {
// Calculate actual name length including null terminator
// Calculate the actual name length including the null terminator.
let actual_name_len = name.as_ref().map_or(0, |name| name.len() + 1);
// Calculate padded name length aligned to sizeof(struct inotify_event)
// Calculate the padded name length aligned to `size_of::<InotifyEventHeader>`.
let pad_name_len = Self::round_event_name_len(actual_name_len);
Self {
header: InotifyEventHeader {
wd,
event,
cookie,
name_len: pad_name_len as u32,
},
name,
}
let header = InotifyEventHeader {
wd,
event: event.bits(),
cookie,
name_len: pad_name_len as u32,
};
Self { header, name }
}
fn wd(&self) -> u32 {
self.header.wd
}
fn event(&self) -> FsEvents {
self.header.event
}
fn cookie(&self) -> u32 {
self.header.cookie
}
fn name_len(&self) -> u32 {
self.header.name_len
}
}
impl InotifyEvent {
/// Rounds up the name length to align with sizeof(struct inotify_event).
/// Rounds up the name length to align with `size_of::<InotifyEventHeader>()`.
///
/// Reference: <https://elixir.bootlin.com/linux/v6.17.8/source/fs/notify/inotify/inotify_user.c#L160>
fn round_event_name_len(name_len: usize) -> usize {
const INOTIFY_EVENT_SIZE: usize = size_of::<InotifyEventHeader>();
(name_len + INOTIFY_EVENT_SIZE - 1) & !(INOTIFY_EVENT_SIZE - 1)
const HEADER_SIZE: usize = size_of::<InotifyEventHeader>(); // 16 bytes
const { assert!(HEADER_SIZE.is_power_of_two()) };
name_len.align_up(HEADER_SIZE)
}
fn total_size(&self) -> usize {
const HEADER_SIZE: usize = size_of::<InotifyEventHeader>(); // 16 bytes
HEADER_SIZE + (self.header.name_len as usize)
}
fn copy_to_user(&self, writer: &mut VmWriter) -> Result<usize> {
let mut total_size = 0;
// Calculate actual name length including null terminator
let actual_name_len = self.name.as_ref().map_or(0, |name| name.len() + 1);
// Calculate padded name length aligned to sizeof(struct inotify_event)
let pad_name_len = Self::round_event_name_len(actual_name_len);
// Write the event header
writer.write_val(&self.wd())?;
writer.write_val(&self.event().bits())?;
writer.write_val(&self.cookie())?;
writer.write_val(&self.name_len())?;
total_size += size_of::<InotifyEventHeader>();
if let Some(name) = self.name.as_ref() {
// Write the actual name bytes
for byte in name.as_bytes() {
writer.write_val(byte)?;
}
// Write null terminator
writer.write_val(&b'\0')?;
total_size += name.len() + 1;
// Fill remaining bytes with zeros for alignment
let padding_len = pad_name_len - actual_name_len;
if padding_len > 0 {
let filled = writer.fill_zeros(padding_len).map_err(|(e, _)| e)?;
total_size += filled;
}
let total_size = self.total_size();
if total_size > writer.avail() {
return_errno_with_message!(Errno::EINVAL, "the buffer is too small");
}
Ok(total_size)
}
// Write the header.
writer.write_val(&self.header)?;
fn get_size(&self) -> usize {
const HEADER_SIZE: usize = size_of::<InotifyEventHeader>(); // 16 bytes
let actual_name_len = self.name.as_ref().map_or(0, |name| name.len() + 1);
let pad_name_len = Self::round_event_name_len(actual_name_len);
HEADER_SIZE + pad_name_len
let Some(name) = self.name.as_ref() else {
debug_assert_eq!(self.header.name_len, 0);
return Ok(total_size);
};
// Write the actual name bytes.
writer.write_fallible(&mut VmReader::from(name.as_bytes()).to_fallible())?;
// Fill remaining bytes with zeros for alignment.
// Note that this also includes the null terminator.
writer.fill_zeros((self.header.name_len as usize) - name.len())?;
Ok(total_size)
}
}