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virtfs file: update cursor position on fd_read (#2070)

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* virtfs file: update cursor position on fd_read

If a handle is backed by InMemoryFile, fd_read (turned into
Handle::read_vectored) doesn't update the cursor position properly and
thus prevents the caller from detecting EOF.

* virtfs file: fd_{pread,pwrite}: update offset in iovec iteration

If multiple iovec's are supplied, fd_pread and fd_pwrite previously
access data at the same offset for each iovec.
This commit is contained in:
Daiki Ueno
2020-07-29 14:19:17 +02:00
committed by GitHub
parent f8f79ba9ca
commit e70f73211d
3 changed files with 92 additions and 6 deletions
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66
crates/test-programs/wasi-tests/src/bin/file_pread_pwrite.rs
View File

@@ -1,5 +1,6 @@
use more_asserts::assert_gt;
use std::{env, process};
use std::convert::TryInto;
use wasi_tests::open_scratch_directory;
unsafe fn test_file_pread_pwrite(dir_fd: wasi::Fd) {
@@ -38,6 +39,71 @@ unsafe fn test_file_pread_pwrite(dir_fd: wasi::Fd) {
assert_eq!(nread, 4, "nread bytes check");
assert_eq!(contents, &[0u8, 1, 2, 3], "written bytes equal read bytes");
// Write all the data through multiple iovecs.
//
// Note that this needs to be done with a loop, because some
// platforms do not support writing multiple iovecs at once.
// See https://github.com/rust-lang/rust/issues/74825.
let contents = &[0u8, 1, 2, 3];
let mut offset = 0usize;
loop {
let mut ciovecs: Vec<wasi::Ciovec> = Vec::new();
let mut remaining = contents.len() - offset;
if remaining > 2 {
ciovecs.push(
wasi::Ciovec {
buf: contents[offset..].as_ptr() as *const _,
buf_len: 2,
},
);
remaining -= 2;
}
ciovecs.push(
wasi::Ciovec {
buf: contents[contents.len() - remaining..].as_ptr() as *const _,
buf_len: remaining
},
);
nwritten =
wasi::fd_pwrite(file_fd, ciovecs.as_slice(), offset.try_into().unwrap()).expect("writing bytes at offset 0");
offset += nwritten;
if offset == contents.len() {
break;
}
}
assert_eq!(offset, 4, "nread bytes check");
// Read all the data through multiple iovecs.
//
// Note that this needs to be done with a loop, because some
// platforms do not support reading multiple iovecs at once.
// See https://github.com/rust-lang/rust/issues/74825.
let contents = &mut [0u8; 4];
let mut offset = 0usize;
loop {
let buffer = &mut [0u8; 4];
let iovecs = &[
wasi::Iovec {
buf: buffer.as_mut_ptr() as *mut _,
buf_len: 2,
},
wasi::Iovec {
buf: buffer[2..].as_mut_ptr() as *mut _,
buf_len: 2
},
];
nread = wasi::fd_pread(file_fd, iovecs, offset as _).expect("reading bytes at offset 0");
if nread == 0 {
break;
}
contents[offset..offset+nread].copy_from_slice(&buffer[0..nread]);
offset += nread;
}
assert_eq!(offset, 4, "nread bytes check");
assert_eq!(contents, &[0u8, 1, 2, 3], "file cursor was overwritten");
let contents = &mut [0u8; 4];
let iovec = wasi::Iovec {
buf: contents.as_mut_ptr() as *mut _,

20
crates/test-programs/wasi-tests/src/bin/file_seek_tell.rs
View File

@@ -25,10 +25,10 @@ unsafe fn test_file_seek_tell(dir_fd: wasi::Fd) {
assert_eq!(offset, 0, "current offset should be 0");
// Write to file
let buf = &[0u8; 100];
let data = &[0u8; 100];
let iov = wasi::Ciovec {
buf: buf.as_ptr() as *const _,
buf_len: buf.len(),
buf: data.as_ptr() as *const _,
buf_len: data.len(),
};
let nwritten = wasi::fd_write(file_fd, &[iov]).expect("writing to a file");
assert_eq!(nwritten, 100, "should write 100 bytes to file");
@@ -65,6 +65,20 @@ unsafe fn test_file_seek_tell(dir_fd: wasi::Fd) {
"errno should be ERRNO_INVAL",
);
// Check that fd_read properly updates the file offset
wasi::fd_seek(file_fd, 0, wasi::WHENCE_SET).expect("seeking to the beginning of the file again");
let buffer = &mut [0u8; 100];
let iovec = wasi::Iovec {
buf: buffer.as_mut_ptr(),
buf_len: buffer.len(),
};
let nread = wasi::fd_read(file_fd, &[iovec]).expect("reading file");
assert_eq!(nread, buffer.len(), "should read {} bytes", buffer.len());
offset = wasi::fd_tell(file_fd).expect("getting file offset after reading");
assert_eq!(offset, 100, "offset after reading should be 100");
wasi::fd_close(file_fd).expect("closing a file");
wasi::path_unlink_file(dir_fd, "file").expect("deleting a file");
}

12
crates/wasi-common/src/virtfs.rs
View File

@@ -78,7 +78,8 @@ impl FileContents for VecFileContents {
fn preadv(&self, iovs: &mut [io::IoSliceMut], offset: types::Filesize) -> Result<usize> {
let mut read_total = 0usize;
for iov in iovs.iter_mut() {
let read = self.pread(iov, offset)?;
let skip: u64 = read_total.try_into().map_err(|_| Errno::Inval)?;
let read = self.pread(iov, offset + skip)?;
read_total = read_total.checked_add(read).expect("FileContents::preadv must not be called when reads could total to more bytes than the return value can hold");
}
Ok(read_total)
@@ -87,7 +88,8 @@ impl FileContents for VecFileContents {
fn pwritev(&mut self, iovs: &[io::IoSlice], offset: types::Filesize) -> Result<usize> {
let mut write_total = 0usize;
for iov in iovs.iter() {
let written = self.pwrite(iov, offset)?;
let skip: u64 = write_total.try_into().map_err(|_| Errno::Inval)?;
let written = self.pwrite(iov, offset + skip)?;
write_total = write_total.checked_add(written).expect("FileContents::pwritev must not be called when writes could total to more bytes than the return value can hold");
}
Ok(write_total)
@@ -255,7 +257,11 @@ impl Handle for InMemoryFile {
fn read_vectored(&self, iovs: &mut [io::IoSliceMut]) -> Result<usize> {
trace!("read_vectored(iovs={:?})", iovs);
trace!(" | *read_start={:?}", self.cursor.get());
self.data.borrow_mut().preadv(iovs, self.cursor.get())
let read = self.data.borrow_mut().preadv(iovs, self.cursor.get())?;
let offset: u64 = read.try_into().map_err(|_| Errno::Inval)?;
let update = self.cursor.get().checked_add(offset).ok_or(Errno::Inval)?;
self.cursor.set(update);
Ok(read)
}
fn seek(&self, offset: SeekFrom) -> Result<types::Filesize> {
let content_len = self.data.borrow().size();