From f110029acfeec1bc40d8764dd4cd1f7424421262 Mon Sep 17 00:00:00 2001
From: Wei Liu <liuwe@microsoft.com>
Date: Wed, 16 Nov 2022 22:29:18 +0000
Subject: [PATCH] block_util: modify or provide safety comments

Signed-off-by: Wei Liu <liuwe@microsoft.com>
---
 block_util/src/async_io.rs  | 3 +++
 block_util/src/raw_async.rs | 7 ++++---
 block_util/src/raw_sync.rs  | 3 +++
 3 files changed, 10 insertions(+), 3 deletions(-)

diff --git a/block_util/src/async_io.rs b/block_util/src/async_io.rs
index 2661f1ffb..f190bbfaa 100644
--- a/block_util/src/async_io.rs
+++ b/block_util/src/async_io.rs
@@ -54,11 +54,13 @@ enum BlockSize {
 impl DiskTopology {
     fn is_block_device(f: &mut File) -> std::io::Result<bool> {
         let mut stat = std::mem::MaybeUninit::<libc::stat>::uninit();
+        // SAFETY: FFI call with a valid fd and buffer
         let ret = unsafe { libc::fstat(f.as_raw_fd(), stat.as_mut_ptr()) };
         if ret != 0 {
             return Err(std::io::Error::last_os_error());
         }
 
+        // SAFETY: stat is valid at this point
         let is_block = unsafe { (*stat.as_ptr()).st_mode & S_IFMT == S_IFBLK };
         Ok(is_block)
     }
@@ -67,6 +69,7 @@ impl DiskTopology {
     #[allow(clippy::useless_conversion)]
     fn query_block_size(f: &mut File, block_size_type: BlockSize) -> std::io::Result<u64> {
         let mut block_size = 0;
+        // SAFETY: FFI call with correct arguments
         let ret = unsafe {
             ioctl(
                 f.as_raw_fd(),
diff --git a/block_util/src/raw_async.rs b/block_util/src/raw_async.rs
index aab48ed87..f1ce670ad 100644
--- a/block_util/src/raw_async.rs
+++ b/block_util/src/raw_async.rs
@@ -81,7 +81,7 @@ impl AsyncIo for RawFileAsync {
     ) -> AsyncIoResult<()> {
         let (submitter, mut sq, _) = self.io_uring.split();
 
-        // Safe because we know the file descriptor is valid and we
+        // SAFETY: we know the file descriptor is valid and we
         // relied on vm-memory to provide the buffer address.
         let _ = unsafe {
             sq.push(
@@ -109,7 +109,7 @@ impl AsyncIo for RawFileAsync {
     ) -> AsyncIoResult<()> {
         let (submitter, mut sq, _) = self.io_uring.split();
 
-        // Safe because we know the file descriptor is valid and we
+        // SAFETY: we know the file descriptor is valid and we
         // relied on vm-memory to provide the buffer address.
         let _ = unsafe {
             sq.push(
@@ -133,7 +133,7 @@ impl AsyncIo for RawFileAsync {
         if let Some(user_data) = user_data {
             let (submitter, mut sq, _) = self.io_uring.split();
 
-            // Safe because we know the file descriptor is valid.
+            // SAFETY: we know the file descriptor is valid.
             let _ = unsafe {
                 sq.push(
                     &opcode::Fsync::new(types::Fd(self.fd))
@@ -148,6 +148,7 @@ impl AsyncIo for RawFileAsync {
             sq.sync();
             submitter.submit().map_err(AsyncIoError::Fsync)?;
         } else {
+            // SAFETY: FFI call with a valid fd
             unsafe { libc::fsync(self.fd) };
         }
 
diff --git a/block_util/src/raw_sync.rs b/block_util/src/raw_sync.rs
index ed6f1be96..fe856a69e 100644
--- a/block_util/src/raw_sync.rs
+++ b/block_util/src/raw_sync.rs
@@ -68,6 +68,7 @@ impl AsyncIo for RawFileSync {
         iovecs: Vec<libc::iovec>,
         user_data: u64,
     ) -> AsyncIoResult<()> {
+        // SAFETY: FFI call with valid arguments
         let result = unsafe {
             libc::preadv(
                 self.fd as libc::c_int,
@@ -92,6 +93,7 @@ impl AsyncIo for RawFileSync {
         iovecs: Vec<libc::iovec>,
         user_data: u64,
     ) -> AsyncIoResult<()> {
+        // SAFETY: FFI call with valid arguments
         let result = unsafe {
             libc::pwritev(
                 self.fd as libc::c_int,
@@ -111,6 +113,7 @@ impl AsyncIo for RawFileSync {
     }
 
     fn fsync(&mut self, user_data: Option<u64>) -> AsyncIoResult<()> {
+        // SAFETY: FFI call
         let result = unsafe { libc::fsync(self.fd as libc::c_int) };
         if result < 0 {
             return Err(AsyncIoError::Fsync(std::io::Error::last_os_error()));