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https://github.com/cloud-hypervisor/cloud-hypervisor.git
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block: qcow: Move iovec scatter/gather helpers to qcow_common
Move scatter_to_iovecs, zero_fill_iovecs and gather_from_iovecs into qcow_common so they can be shared with the upcoming qcow_async backend. These helpers treat an iovec array as a flat byte stream and are used by both read_vectored and write_vectored code paths. Signed-off-by: Anatol Belski <anbelski@linux.microsoft.com>
This commit is contained in:
Anatol Belski
committed by
Rob Bradford
Rob Bradford
parent
7f3dfe2154
commit
81f43f96c3
@@ -9,8 +9,9 @@
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//! Position-independent I/O (`pread_exact`, `pwrite_all`) and iovec
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//! scatter/gather helpers used by both `qcow_sync` and `qcow_async`.
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use std::io;
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use std::cmp::min;
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use std::os::fd::RawFd;
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use std::{io, ptr, slice};
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// -- Position independent I/O helpers --
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//
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@@ -65,3 +66,96 @@ pub fn pwrite_all(fd: RawFd, buf: &[u8], offset: u64) -> io::Result<()> {
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}
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Ok(())
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}
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// -- iovec helper functions --
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//
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// Operate on the iovec array as a flat byte stream.
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/// Copy data into iovecs starting at the given byte offset.
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///
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/// # Safety
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/// Caller must ensure iovecs point to valid, writable memory of sufficient size.
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pub unsafe fn scatter_to_iovecs(iovecs: &[libc::iovec], start: usize, data: &[u8]) {
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let mut remaining = data;
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let mut pos = 0usize;
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for iov in iovecs {
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let iov_end = pos + iov.iov_len;
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if iov_end <= start || remaining.is_empty() {
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pos = iov_end;
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continue;
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}
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let iov_start = start.saturating_sub(pos);
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let available = iov.iov_len - iov_start;
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let count = min(available, remaining.len());
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// SAFETY: iov_base is valid for iov_len bytes per caller contract.
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unsafe {
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let dst = (iov.iov_base as *mut u8).add(iov_start);
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ptr::copy_nonoverlapping(remaining.as_ptr(), dst, count);
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}
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remaining = &remaining[count..];
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if remaining.is_empty() {
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break;
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}
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pos = iov_end;
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}
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}
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/// Zero fill iovecs starting at the given byte offset for the given length.
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///
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/// # Safety
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/// Caller must ensure iovecs point to valid, writable memory of sufficient size.
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pub unsafe fn zero_fill_iovecs(iovecs: &[libc::iovec], start: usize, len: usize) {
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let mut remaining = len;
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let mut pos = 0usize;
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for iov in iovecs {
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let iov_end = pos + iov.iov_len;
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if iov_end <= start || remaining == 0 {
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pos = iov_end;
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continue;
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}
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let iov_start = start.saturating_sub(pos);
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let available = iov.iov_len - iov_start;
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let count = min(available, remaining);
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// SAFETY: iov_base is valid for iov_len bytes per caller contract.
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unsafe {
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let dst = (iov.iov_base as *mut u8).add(iov_start);
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ptr::write_bytes(dst, 0, count);
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}
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remaining -= count;
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if remaining == 0 {
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break;
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}
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pos = iov_end;
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}
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}
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/// Gather bytes from iovecs starting at the given byte offset into a Vec.
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///
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/// # Safety
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/// Caller must ensure iovecs point to valid, readable memory of sufficient size.
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pub unsafe fn gather_from_iovecs(iovecs: &[libc::iovec], start: usize, len: usize) -> Vec<u8> {
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let mut result = Vec::with_capacity(len);
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let mut remaining = len;
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let mut pos = 0usize;
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for iov in iovecs {
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let iov_end = pos + iov.iov_len;
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if iov_end <= start || remaining == 0 {
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pos = iov_end;
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continue;
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}
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let iov_start = start.saturating_sub(pos);
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let available = iov.iov_len - iov_start;
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let count = min(available, remaining);
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// SAFETY: iov_base is valid for iov_len bytes per caller contract.
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unsafe {
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let src = (iov.iov_base as *const u8).add(iov_start);
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result.extend_from_slice(slice::from_raw_parts(src, count));
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}
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remaining -= count;
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if remaining == 0 {
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break;
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}
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pos = iov_end;
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}
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result
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}
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@@ -7,7 +7,7 @@ use std::collections::VecDeque;
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use std::fs::File;
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use std::os::fd::{AsFd, AsRawFd, BorrowedFd, OwnedFd};
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use std::sync::Arc;
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use std::{fmt, io, ptr, slice};
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use std::{fmt, io};
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use vmm_sys_util::eventfd::EventFd;
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use vmm_sys_util::write_zeroes::{PunchHole, WriteZeroesAt};
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@@ -22,7 +22,9 @@ use crate::qcow::qcow_raw_file::QcowRawFile;
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use crate::qcow::{
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BackingFile, BackingKind, Error as QcowError, MAX_NESTING_DEPTH, RawFile, parse_qcow,
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};
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use crate::qcow_common::{pread_exact, pwrite_all};
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use crate::qcow_common::{
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gather_from_iovecs, pread_exact, pwrite_all, scatter_to_iovecs, zero_fill_iovecs,
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};
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/// Raw backing file using pread64 on a duplicated fd.
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struct RawBacking {
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@@ -323,95 +325,6 @@ impl QcowSync {
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}
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}
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/// Copy data into iovecs starting at the given byte offset.
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///
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/// # Safety
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/// Caller must ensure iovecs point to valid, writable memory of sufficient size.
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unsafe fn scatter_to_iovecs(iovecs: &[libc::iovec], start: usize, data: &[u8]) {
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let mut remaining = data;
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let mut pos = 0usize;
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for iov in iovecs {
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let iov_end = pos + iov.iov_len;
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if iov_end <= start || remaining.is_empty() {
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pos = iov_end;
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continue;
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}
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let iov_start = start.saturating_sub(pos);
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let available = iov.iov_len - iov_start;
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let count = min(available, remaining.len());
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// SAFETY: iov_base is valid for iov_len bytes per caller contract.
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unsafe {
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let dst = (iov.iov_base as *mut u8).add(iov_start);
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ptr::copy_nonoverlapping(remaining.as_ptr(), dst, count);
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}
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remaining = &remaining[count..];
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if remaining.is_empty() {
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break;
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}
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pos = iov_end;
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}
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}
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/// Zero fill iovecs starting at the given byte offset for the given length.
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///
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/// # Safety
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/// Caller must ensure iovecs point to valid, writable memory of sufficient size.
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unsafe fn zero_fill_iovecs(iovecs: &[libc::iovec], start: usize, len: usize) {
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let mut remaining = len;
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let mut pos = 0usize;
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for iov in iovecs {
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let iov_end = pos + iov.iov_len;
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if iov_end <= start || remaining == 0 {
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pos = iov_end;
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continue;
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}
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let iov_start = start.saturating_sub(pos);
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let available = iov.iov_len - iov_start;
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let count = min(available, remaining);
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// SAFETY: iov_base is valid for iov_len bytes per caller contract.
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unsafe {
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let dst = (iov.iov_base as *mut u8).add(iov_start);
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ptr::write_bytes(dst, 0, count);
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}
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remaining -= count;
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if remaining == 0 {
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break;
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}
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pos = iov_end;
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}
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}
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/// Gather bytes from iovecs starting at the given byte offset into a Vec.
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///
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/// # Safety
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/// Caller must ensure iovecs point to valid, readable memory of sufficient size.
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unsafe fn gather_from_iovecs(iovecs: &[libc::iovec], start: usize, len: usize) -> Vec<u8> {
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let mut result = Vec::with_capacity(len);
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let mut remaining = len;
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let mut pos = 0usize;
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for iov in iovecs {
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let iov_end = pos + iov.iov_len;
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if iov_end <= start || remaining == 0 {
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pos = iov_end;
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continue;
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}
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let iov_start = start.saturating_sub(pos);
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let available = iov.iov_len - iov_start;
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let count = min(available, remaining);
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// SAFETY: iov_base is valid for iov_len bytes per caller contract.
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unsafe {
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let src = (iov.iov_base as *const u8).add(iov_start);
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result.extend_from_slice(slice::from_raw_parts(src, count));
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}
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remaining -= count;
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if remaining == 0 {
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break;
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}
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pos = iov_end;
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}
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result
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}
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impl AsyncIo for QcowSync {
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fn notifier(&self) -> &EventFd {
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&self.eventfd
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