add pread on linux

lib/wasi/src/syscalls/mod.rs

@@ -248,6 +248,7 @@ pub fn fd_filestat_set_times(
 ) -> __wasi_errno_t {
     unimplemented!()
 }
+
 pub fn fd_pread(
     ctx: &mut Ctx,
     fd: __wasi_fd_t,
@@ -256,8 +257,17 @@ pub fn fd_pread(
     offset: __wasi_filesize_t,
     nread: WasmPtr<u32>,
 ) -> __wasi_errno_t {
-    unimplemented!()
+    let memory = ctx.memory(0);
+
+    if let ((Some(iov_cells), Some(nread_cell))) =
+        (iovs.deref(memory, 0, iovs_len), nread.deref(memory))
+    {
+        platform_fd_pread(fd, iov_cells, iovs_len, offset, nread_cell)
+    } else {
+        __WASI_EFAULT
+    }
 }
+
 pub fn fd_prestat_get(
     ctx: &mut Ctx,
     fd: __wasi_fd_t,

lib/wasi/src/syscalls/types.rs

@@ -1,6 +1,7 @@
 #![allow(non_camel_case_types)]
 
 use crate::ptr::{Array, WasmPtr};
+use std::mem;
 use wasmer_runtime_core::types::{ValueError, ValueType};
 
 pub type __wasi_advice_t = u8;
@@ -212,6 +213,25 @@ pub struct __wasi_iovec_t {
     pub buf_len: u32,
 }
 
+impl ValueType for __wasi_iovec_t {
+    fn into_le(self, buffer: &mut [u8]) {
+        self.buf
+            .into_le(&mut buffer[..mem::size_of::<WasmPtr<u8, Array>>()]);
+        self.buf_len
+            .into_le(&mut buffer[mem::size_of::<WasmPtr<u8, Array>>()..]);
+    }
+
+    fn from_le(buffer: &[u8]) -> Result<Self, ValueError> {
+        if buffer.len() >= mem::size_of::<__wasi_iovec_t>() {
+            let buf = ValueType::from_le(&buffer[..mem::size_of::<WasmPtr<u8, Array>>()])?;
+            let buf_len = ValueType::from_le(&buffer[mem::size_of::<WasmPtr<u8, Array>>()..])?;
+            Ok(Self { buf, buf_len })
+        } else {
+            Err(ValueError::BufferTooSmall)
+        }
+    }
+}
+
 pub type __wasi_linkcount_t = u32;
 
 pub type __wasi_lookupflags_t = u32;

lib/wasi/src/syscalls/unix/linux.rs

@@ -1 +1,27 @@
+use crate::syscalls::types::*;
+use std::cell::Cell;
 
+use libc::preadv;
+
+pub fn platform_fd_pread(
+    fd: __wasi_fd_t,
+    iovs: &[Cell<__wasi_iovec_t>],
+    iovs_len: u32,
+    offset: __wasi_filesize_t,
+    nread: &Cell<u32>,
+) -> __wasi_errno_t {
+    let (result, iovec) = unsafe {
+        let mut iovec = vec![mem::uninitialized(); iovs_len as usize];
+        (preadv(fd, &mut iovec, iovs_len, offset), iovec)
+    };
+    nread.set(result);
+    for (arr_cell, i) in iov_arr.iter().enumerate() {
+        let wasi_iovec = __wasi_iovec_t {
+            buf: iovec[i] as _,
+            buf_len: iovec[i].iov_len as u32,
+        };
+        arr_cell.set(wasi_iovec);
+    }
+
+    __WASI_ESUCCESS
+}

lib/wasi/src/syscalls/unix/macos.rs

@@ -1 +1,12 @@
+use crate::syscalls::types::*;
+use std::cell::Cell;
 
+pub fn platform_fd_pread(
+    fd: __wasi_fd_t,
+    iovs: &[Cell<__wasi_iovec_t>],
+    iovs_len: u32,
+    offset: __wasi_filesize_t,
+    nread: &Cell<u32>,
+) -> __wasi_errno_t {
+    unimplemented!()
+}

lib/wasi/src/syscalls/windows.rs

@@ -15,3 +15,13 @@ pub fn platform_clock_time_get(
 ) -> __wasi_errno_t {
     unimplemented!()
 }
+
+pub fn platform_fd_pread(
+    fd: __wasi_fd_t,
+    iovs: &[Cell<__wasi_iovec_t>],
+    iovs_len: u32,
+    offset: __wasi_filesize_t,
+    nread: &Cell<u32>,
+) -> __wasi_errno_t {
+    unimplemented!()
+}