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wasi-common: don't rely on platform dependent "NUL" device

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If stdio is not inherited nor associated with a file, WasiCtxBuilder
tries to open "/dev/null" ("NUL" on Windows) and attach stdio to it.
While most platforms today support those device files, it would be
good to avoid unnecessary access to the host device if possible.  This
patch instead uses a virtual Handle that emulates the "NUL" device.
This commit is contained in:
Daiki Ueno
2020-06-10 16:37:42 +02:00
parent 4ebbcb82a9
commit 65ebfc3a03
6 changed files with 67 additions and 38 deletions
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8
crates/wasi-common/src/ctx.rs
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@@ -2,7 +2,7 @@ use crate::entry::{Entry, EntryHandle};
use crate::fdpool::FdPool;
use crate::handle::Handle;
use crate::sys::osdir::OsDir;
use crate::sys::osother::{OsOther, OsOtherExt};
use crate::sys::stdio::NullDevice;
use crate::sys::stdio::{Stderr, StderrExt, Stdin, StdinExt, Stdout, StdoutExt};
use crate::virtfs::{VirtualDir, VirtualDirEntry};
use crate::wasi::types;
@@ -136,9 +136,9 @@ pub struct WasiCtxBuilder {
impl WasiCtxBuilder {
/// Builder for a new `WasiCtx`.
pub fn new() -> Self {
let stdin = Some(PendingEntry::Thunk(OsOther::from_null));
let stdout = Some(PendingEntry::Thunk(OsOther::from_null));
let stderr = Some(PendingEntry::Thunk(OsOther::from_null));
let stdin = Some(PendingEntry::Handle(Box::new(NullDevice::new())));
let stdout = Some(PendingEntry::Handle(Box::new(NullDevice::new())));
let stderr = Some(PendingEntry::Handle(Box::new(NullDevice::new())));
Self {
stdin,