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Refactor use of Refs and RefMuts in wasi-common (#1412)

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* Refactor use of Refs and RefMuts in wasi-common

This commit refactors the use of `Ref`s and `RefMut`s in `wasi-common`.
Now, `Entry` is stored behind an `Rc` inside the `EntryTable`. The `Entry`
itself on the other hand now stores rights behind a `RefCell` and the
descriptor as `Rc<RefCell<..>>` combo to enable easy reference tracking
and interior mutability which is required down the line in a couple of
syscalls. In essence, this implies that we no longer have need for
mutable accessor to `Entry` from `WasiCtx`, and so all related methods
go away (`get_entry_mut`, etc.).

While here, I've also simplified handling and aggregating of rights on
the `Entry` object. Instead of storing base and inheriting rights as
separate fields, they are now aggregated into one struct `EntryRights`
which features convenient constructors for each possible combination; i.e.,
when only base rights are set, or both base and inheriting are set, or
both are left as empty. Since we do need to be able to mutate those
rights down the line in `fdstat_set_rights` syscall, this object
is kept behind a `RefCell` (note no `Rc` since we don't need to pass it
around anywhere).

The descriptor field in `Entry` is now kept behind `Rc<RefCell<..>>` combo
since we not only need to mutate it down the line, but we also need to
be able to pass it around (as part of the machinery making `poll_oneoff`
work).

I've also removed `as_file` and `try_clone` methods on `Descriptor` struct
since they were adding more noise than necessary, and making them work
with `Rc` was unnecessarily complicated.

Finally, I've converted the `get_dir_from_os_handle` function into a
method attached to the `OsHandle` itself, called `dir_stream`. IMHO,
it makes more sense to have it there directly as a method than as a separate
function.

* Use Cell for types that are Copy
This commit is contained in:
Jakub Konka
2020-03-27 09:34:52 +01:00
committed by GitHub
parent 092538cc54
commit 5c51940100
20 changed files with 446 additions and 550 deletions
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61
crates/wasi-common/src/virtfs.rs
View File

@@ -1,7 +1,7 @@
use crate::wasi::{self, types, Errno, Result, RightsExt};
use filetime::FileTime;
use log::trace;
use std::cell::RefCell;
use std::cell::{Cell, RefCell};
use std::collections::hash_map::Entry;
use std::collections::HashMap;
use std::convert::TryInto;
@@ -127,7 +127,7 @@ pub(crate) trait VirtualFile: MovableFile {
Err(Errno::Badf)
}
fn fdstat_set_flags(&mut self, _fdflags: types::Fdflags) -> Result<()> {
fn fdstat_set_flags(&self, _fdflags: types::Fdflags) -> Result<Option<Box<dyn VirtualFile>>> {
Err(Errno::Badf)
}
@@ -254,26 +254,26 @@ impl VecFileContents {
/// a filesystem wherein a file descriptor is one view into a possibly-shared underlying collection
/// of data and permissions on a filesystem.
pub struct InMemoryFile {
cursor: RefCell<types::Filesize>,
cursor: Cell<types::Filesize>,
parent: Rc<RefCell<Option<Box<dyn VirtualFile>>>>,
fd_flags: types::Fdflags,
fd_flags: Cell<types::Fdflags>,
data: Rc<RefCell<Box<dyn FileContents>>>,
}
impl InMemoryFile {
pub fn memory_backed() -> Self {
Self {
cursor: RefCell::new(0),
cursor: Cell::new(0),
parent: Rc::new(RefCell::new(None)),
fd_flags: types::Fdflags::empty(),
fd_flags: Cell::new(types::Fdflags::empty()),
data: Rc::new(RefCell::new(Box::new(VecFileContents::new()))),
}
}
pub fn new(contents: Box<dyn FileContents>) -> Self {
Self {
cursor: RefCell::new(0),
fd_flags: types::Fdflags::empty(),
cursor: Cell::new(0),
fd_flags: Cell::new(types::Fdflags::empty()),
parent: Rc::new(RefCell::new(None)),
data: Rc::new(RefCell::new(contents)),
}
@@ -288,13 +288,13 @@ impl MovableFile for InMemoryFile {
impl VirtualFile for InMemoryFile {
fn fdstat_get(&self) -> types::Fdflags {
self.fd_flags
self.fd_flags.get()
}
fn try_clone(&self) -> io::Result<Box<dyn VirtualFile>> {
Ok(Box::new(Self {
cursor: RefCell::new(0),
fd_flags: self.fd_flags,
cursor: Cell::new(0),
fd_flags: self.fd_flags.clone(),
parent: Rc::clone(&self.parent),
data: Rc::clone(&self.data),
}))
@@ -351,23 +351,27 @@ impl VirtualFile for InMemoryFile {
Err(Errno::Notdir)
}
fn fdstat_set_flags(&mut self, fdflags: types::Fdflags) -> Result<()> {
self.fd_flags = fdflags;
Ok(())
fn fdstat_set_flags(&self, fdflags: types::Fdflags) -> Result<Option<Box<dyn VirtualFile>>> {
self.fd_flags.set(fdflags);
// We return None here to signal that the operation succeeded on the original
// file descriptor and mutating the original WASI Descriptor is thus unnecessary.
// This is needed as on Windows this operation required reopening a file. So we're
// adhering to the common signature required across platforms.
Ok(None)
}
fn write_vectored(&self, iovs: &[io::IoSlice]) -> Result<usize> {
trace!("write_vectored(iovs={:?})", iovs);
let mut data = self.data.borrow_mut();
let append_mode = self.fd_flags.contains(&types::Fdflags::APPEND);
trace!(" | fd_flags={}", self.fd_flags);
let append_mode = self.fd_flags.get().contains(&types::Fdflags::APPEND);
trace!(" | fd_flags={}", self.fd_flags.get());
// If this file is in append mode, we write to the end.
let write_start = if append_mode {
data.size()
} else {
*self.cursor.borrow()
self.cursor.get()
};
let max_size = iovs
@@ -396,7 +400,8 @@ impl VirtualFile for InMemoryFile {
// If we are not appending, adjust the cursor appropriately for the write, too. This can't
// overflow, as we checked against that before writing any data.
if !append_mode {
*self.cursor.borrow_mut() += written as u64;
let update = self.cursor.get() + written as u64;
self.cursor.set(update);
}
Ok(written)
@@ -404,8 +409,8 @@ impl VirtualFile for InMemoryFile {
fn read_vectored(&self, iovs: &mut [io::IoSliceMut]) -> Result<usize> {
trace!("read_vectored(iovs={:?})", iovs);
trace!(" | *read_start={:?}", self.cursor);
self.data.borrow_mut().preadv(iovs, *self.cursor.borrow())
trace!(" | *read_start={:?}", self.cursor.get());
self.data.borrow_mut().preadv(iovs, self.cursor.get())
}
fn preadv(&self, buf: &mut [io::IoSliceMut], offset: types::Filesize) -> Result<usize> {
@@ -422,30 +427,30 @@ impl VirtualFile for InMemoryFile {
SeekFrom::Current(offset) => {
let new_cursor = if offset < 0 {
self.cursor
.borrow()
.get()
.checked_sub(offset.wrapping_neg() as u64)
.ok_or(Errno::Inval)?
} else {
self.cursor
.borrow()
.get()
.checked_add(offset as u64)
.ok_or(Errno::Inval)?
};
*self.cursor.borrow_mut() = std::cmp::min(content_len, new_cursor);
self.cursor.set(std::cmp::min(content_len, new_cursor));
}
SeekFrom::End(offset) => {
// A negative offset from the end would be past the end of the file,
let offset: u64 = offset.try_into().map_err(|_| Errno::Inval)?;
*self.cursor.borrow_mut() = content_len.saturating_sub(offset);
self.cursor.set(content_len.saturating_sub(offset));
}
SeekFrom::Start(offset) => {
// A negative offset from the end would be before the start of the file.
let offset: u64 = offset.try_into().map_err(|_| Errno::Inval)?;
*self.cursor.borrow_mut() = std::cmp::min(content_len, offset);
self.cursor.set(std::cmp::min(content_len, offset));
}
}
Ok(*self.cursor.borrow())
Ok(self.cursor.get())
}
fn advise(
@@ -656,8 +661,8 @@ impl VirtualFile for VirtualDir {
path.display()
);
let mut file = Box::new(InMemoryFile::memory_backed());
file.fd_flags = fd_flags;
let file = Box::new(InMemoryFile::memory_backed());
file.fd_flags.set(fd_flags);
file.set_parent(Some(self.try_clone().expect("can clone self")));
v.insert(file).try_clone().map_err(Into::into)
} else {