refactor(virtual_file): take owned buffer in VirtualFile::write_all

pageserver/src/deletion_queue.rs

@@ -234,7 +234,7 @@ impl DeletionHeader {
         let header_bytes = serde_json::to_vec(self).context("serialize deletion header")?;
         let header_path = conf.deletion_header_path();
         let temp_path = path_with_suffix_extension(&header_path, TEMP_SUFFIX);
-        VirtualFile::crashsafe_overwrite(&header_path, &temp_path, &header_bytes)
+        VirtualFile::crashsafe_overwrite(&header_path, &temp_path, header_bytes)
             .await
             .maybe_fatal_err("save deletion header")?;
 
@@ -325,7 +325,7 @@ impl DeletionList {
         let temp_path = path_with_suffix_extension(&path, TEMP_SUFFIX);
 
         let bytes = serde_json::to_vec(self).expect("Failed to serialize deletion list");
-        VirtualFile::crashsafe_overwrite(&path, &temp_path, &bytes)
+        VirtualFile::crashsafe_overwrite(&path, &temp_path, bytes)
             .await
             .maybe_fatal_err("save deletion list")
             .map_err(Into::into)

pageserver/src/tenant.rs

@@ -2880,7 +2880,7 @@ impl Tenant {
         let config_path = config_path.to_owned();
         tokio::task::spawn_blocking(move || {
             Handle::current().block_on(async move {
-                let conf_content = conf_content.as_bytes();
+                let conf_content = conf_content.into_bytes();
                 VirtualFile::crashsafe_overwrite(&config_path, &temp_path, conf_content)
                     .await
                     .with_context(|| {
@@ -2917,7 +2917,7 @@ impl Tenant {
         let target_config_path = target_config_path.to_owned();
         tokio::task::spawn_blocking(move || {
             Handle::current().block_on(async move {
-                let conf_content = conf_content.as_bytes();
+                let conf_content = conf_content.into_bytes();
                 VirtualFile::crashsafe_overwrite(&target_config_path, &temp_path, conf_content)
                     .await
                     .with_context(|| {

pageserver/src/tenant/blob_io.rs

@@ -131,27 +131,23 @@ impl<const BUFFERED: bool> BlobWriter<BUFFERED> {
         &mut self,
         src_buf: B,
     ) -> (B::Buf, Result<(), Error>) {
-        let src_buf_len = src_buf.bytes_init();
-        let (src_buf, res) = if src_buf_len > 0 {
-            let src_buf = src_buf.slice(0..src_buf_len);
-            let res = self.inner.write_all(&src_buf).await;
-            let src_buf = Slice::into_inner(src_buf);
-            (src_buf, res)
-        } else {
-            let res = self.inner.write_all(&[]).await;
-            (Slice::into_inner(src_buf.slice_full()), res)
+        let (src_buf, res) = self.inner.write_all(src_buf).await;
+        let nbytes = match res {
+            Ok(nbytes) => nbytes,
+            Err(e) => return (src_buf, Err(e)),
         };
-        if let Ok(()) = &res {
-            self.offset += src_buf_len as u64;
-        }
-        (src_buf, res)
+        self.offset += nbytes as u64;
+        (src_buf, Ok(()))
     }
 
     #[inline(always)]
     /// Flushes the internal buffer to the underlying `VirtualFile`.
     pub async fn flush_buffer(&mut self) -> Result<(), Error> {
-        self.inner.write_all(&self.buf).await?;
-        self.buf.clear();
+        let buf = std::mem::take(&mut self.buf);
+        let (mut buf, res) = self.inner.write_all(buf).await;
+        res?;
+        buf.clear();
+        self.buf = buf;
         Ok(())
     }
 

pageserver/src/tenant/metadata.rs

@@ -279,7 +279,7 @@ pub async fn save_metadata(
     let path = conf.metadata_path(tenant_shard_id, timeline_id);
     let temp_path = path_with_suffix_extension(&path, TEMP_FILE_SUFFIX);
     let metadata_bytes = data.to_bytes().context("serialize metadata")?;
-    VirtualFile::crashsafe_overwrite(&path, &temp_path, &metadata_bytes)
+    VirtualFile::crashsafe_overwrite(&path, &temp_path, metadata_bytes)
         .await
         .context("write metadata")?;
     Ok(())

pageserver/src/tenant/secondary/downloader.rs

@@ -486,7 +486,7 @@ impl<'a> TenantDownloader<'a> {
         let heatmap_path_bg = heatmap_path.clone();
         tokio::task::spawn_blocking(move || {
             tokio::runtime::Handle::current().block_on(async move {
-                VirtualFile::crashsafe_overwrite(&heatmap_path_bg, &temp_path, &heatmap_bytes).await
+                VirtualFile::crashsafe_overwrite(&heatmap_path_bg, &temp_path, heatmap_bytes).await
             })
         })
         .await

pageserver/src/tenant/storage_layer/delta_layer.rs

@@ -461,7 +461,8 @@ impl DeltaLayerWriterInner {
         file.seek(SeekFrom::Start(index_start_blk as u64 * PAGE_SZ as u64))
             .await?;
         for buf in block_buf.blocks {
-            file.write_all(buf.as_ref()).await?;
+            let (_buf, res) = file.write_all(buf).await;
+            res?;
         }
         assert!(self.lsn_range.start < self.lsn_range.end);
         // Fill in the summary on blk 0
@@ -476,17 +477,12 @@ impl DeltaLayerWriterInner {
             index_root_blk,
         };
 
-        let mut buf = smallvec::SmallVec::<[u8; PAGE_SZ]>::new();
+        let mut buf = Vec::with_capacity(PAGE_SZ);
+        // TODO: could use smallvec here but it's a pain with Slice<T>
         Summary::ser_into(&summary, &mut buf)?;
-        if buf.spilled() {
-            // This is bad as we only have one free block for the summary
-            warn!(
-                "Used more than one page size for summary buffer: {}",
-                buf.len()
-            );
-        }
         file.seek(SeekFrom::Start(0)).await?;
-        file.write_all(&buf).await?;
+        let (_buf, res) = file.write_all(buf).await;
+        res?;
 
         let metadata = file
             .metadata()
@@ -679,18 +675,12 @@ impl DeltaLayer {
 
         let new_summary = rewrite(actual_summary);
 
-        let mut buf = smallvec::SmallVec::<[u8; PAGE_SZ]>::new();
+        let mut buf = Vec::with_capacity(PAGE_SZ);
+        // TODO: could use smallvec here, but it's a pain with Slice<T>
         Summary::ser_into(&new_summary, &mut buf).context("serialize")?;
-        if buf.spilled() {
-            // The code in DeltaLayerWriterInner just warn!()s for this.
-            // It should probably error out as well.
-            return Err(RewriteSummaryError::Other(anyhow::anyhow!(
-                "Used more than one page size for summary buffer: {}",
-                buf.len()
-            )));
-        }
         file.seek(SeekFrom::Start(0)).await?;
-        file.write_all(&buf).await?;
+        let (_buf, res) = file.write_all(buf).await;
+        res?;
         Ok(())
     }
 }

pageserver/src/tenant/storage_layer/image_layer.rs

@@ -341,18 +341,12 @@ impl ImageLayer {
 
         let new_summary = rewrite(actual_summary);
 
-        let mut buf = smallvec::SmallVec::<[u8; PAGE_SZ]>::new();
+        let mut buf = Vec::with_capacity(PAGE_SZ);
+        // TODO: could use smallvec here but it's a pain with Slice<T>
         Summary::ser_into(&new_summary, &mut buf).context("serialize")?;
-        if buf.spilled() {
-            // The code in ImageLayerWriterInner just warn!()s for this.
-            // It should probably error out as well.
-            return Err(RewriteSummaryError::Other(anyhow::anyhow!(
-                "Used more than one page size for summary buffer: {}",
-                buf.len()
-            )));
-        }
         file.seek(SeekFrom::Start(0)).await?;
-        file.write_all(&buf).await?;
+        let (_buf, res) = file.write_all(buf).await;
+        res?;
         Ok(())
     }
 }
@@ -555,7 +549,8 @@ impl ImageLayerWriterInner {
             .await?;
         let (index_root_blk, block_buf) = self.tree.finish()?;
         for buf in block_buf.blocks {
-            file.write_all(buf.as_ref()).await?;
+            let (_buf, res) = file.write_all(buf).await;
+            res?;
         }
 
         // Fill in the summary on blk 0
@@ -570,17 +565,12 @@ impl ImageLayerWriterInner {
             index_root_blk,
         };
 
-        let mut buf = smallvec::SmallVec::<[u8; PAGE_SZ]>::new();
+        let mut buf = Vec::with_capacity(PAGE_SZ);
+        // TODO: could use smallvec here but it's a pain with Slice<T>
         Summary::ser_into(&summary, &mut buf)?;
-        if buf.spilled() {
-            // This is bad as we only have one free block for the summary
-            warn!(
-                "Used more than one page size for summary buffer: {}",
-                buf.len()
-            );
-        }
         file.seek(SeekFrom::Start(0)).await?;
-        file.write_all(&buf).await?;
+        let (_buf, res) = file.write_all(buf).await;
+        res?;
 
         let metadata = file
             .metadata()

pageserver/src/virtual_file.rs

@@ -19,7 +19,7 @@ use once_cell::sync::OnceCell;
 use pageserver_api::shard::TenantShardId;
 use std::fs::{self, File};
 use std::io::{Error, ErrorKind, Seek, SeekFrom};
-use tokio_epoll_uring::IoBufMut;
+use tokio_epoll_uring::{BoundedBuf, IoBufMut, Slice};
 
 use std::os::fd::{AsRawFd, FromRawFd, IntoRawFd, OwnedFd, RawFd};
 use std::os::unix::fs::FileExt;
@@ -410,10 +410,10 @@ impl VirtualFile {
     /// step, the tmp path is renamed to the final path. As renames are
     /// atomic, a crash during the write operation will never leave behind a
     /// partially written file.
-    pub async fn crashsafe_overwrite(
+    pub async fn crashsafe_overwrite<B: BoundedBuf>(
         final_path: &Utf8Path,
         tmp_path: &Utf8Path,
-        content: &[u8],
+        content: B,
     ) -> std::io::Result<()> {
         let Some(final_path_parent) = final_path.parent() else {
             return Err(std::io::Error::from_raw_os_error(
@@ -430,7 +430,8 @@ impl VirtualFile {
                 .create_new(true),
         )
         .await?;
-        file.write_all(content).await?;
+        let (_content, res) = file.write_all(content).await;
+        res?;
         file.sync_all().await?;
         drop(file); // before the rename, that's important!
                     // renames are atomic
@@ -601,23 +602,36 @@ impl VirtualFile {
         Ok(())
     }
 
-    pub async fn write_all(&mut self, mut buf: &[u8]) -> Result<(), Error> {
+    /// Writes `buf.slice(0..buf.bytes_init())`.
+    /// Returns the IoBuf that is underlying the BoundedBuf `buf`.
+    /// I.e., the returned value's `bytes_init()` method returns something different than the `bytes_init()` that was passed in.
+    /// It's quite brittle and easy to mis-use, so, we return the size in the Ok() variant.
+    pub async fn write_all<B: BoundedBuf>(&mut self, buf: B) -> (B::Buf, Result<usize, Error>) {
+        let nbytes = buf.bytes_init();
+        if nbytes == 0 {
+            return (Slice::into_inner(buf.slice_full()), Ok(0));
+        }
+        let mut buf = buf.slice(0..nbytes);
         while !buf.is_empty() {
-            match self.write(buf).await {
+            // TODO: push `Slice` further down
+            match self.write(&buf).await {
                 Ok(0) => {
-                    return Err(Error::new(
-                        std::io::ErrorKind::WriteZero,
-                        "failed to write whole buffer",
-                    ));
+                    return (
+                        Slice::into_inner(buf),
+                        Err(Error::new(
+                            std::io::ErrorKind::WriteZero,
+                            "failed to write whole buffer",
+                        )),
+                    );
                 }
                 Ok(n) => {
-                    buf = &buf[n..];
+                    buf = buf.slice(n..);
                 }
                 Err(ref e) if e.kind() == std::io::ErrorKind::Interrupted => {}
-                Err(e) => return Err(e),
+                Err(e) => return (Slice::into_inner(buf), Err(e)),
             }
         }
-        Ok(())
+        (Slice::into_inner(buf), Ok(nbytes))
     }
 
     async fn write(&mut self, buf: &[u8]) -> Result<usize, std::io::Error> {
@@ -676,7 +690,6 @@ where
     F: FnMut(tokio_epoll_uring::Slice<B>, u64) -> Fut,
     Fut: std::future::Future<Output = (tokio_epoll_uring::Slice<B>, std::io::Result<usize>)>,
 {
-    use tokio_epoll_uring::BoundedBuf;
     let mut buf: tokio_epoll_uring::Slice<B> = buf.slice_full(); // includes all the uninitialized memory
     while buf.bytes_total() != 0 {
         let res;
@@ -1063,10 +1076,19 @@ mod tests {
                 MaybeVirtualFile::File(file) => file.seek(pos),
             }
         }
-        async fn write_all(&mut self, buf: &[u8]) -> Result<(), Error> {
+        async fn write_all<B: BoundedBuf>(&mut self, buf: B) -> Result<(), Error> {
             match self {
-                MaybeVirtualFile::VirtualFile(file) => file.write_all(buf).await,
-                MaybeVirtualFile::File(file) => file.write_all(buf),
+                MaybeVirtualFile::VirtualFile(file) => {
+                    let (_buf, res) = file.write_all(buf).await;
+                    res.map(|_| ())
+                }
+                MaybeVirtualFile::File(file) => {
+                    let buf_len = buf.bytes_init();
+                    if buf_len == 0 {
+                        return Ok(());
+                    }
+                    file.write_all(&buf.slice(0..buf_len))
+                }
             }
         }
 
@@ -1141,7 +1163,7 @@ mod tests {
                 .to_owned(),
         )
         .await?;
-        file_a.write_all(b"foobar").await?;
+        file_a.write_all(b"foobar".to_vec()).await?;
 
         // cannot read from a file opened in write-only mode
         let _ = file_a.read_string().await.unwrap_err();
@@ -1150,7 +1172,7 @@ mod tests {
         let mut file_a = openfunc(path_a, OpenOptions::new().read(true).to_owned()).await?;
 
         // cannot write to a file opened in read-only mode
-        let _ = file_a.write_all(b"bar").await.unwrap_err();
+        let _ = file_a.write_all(b"bar".to_vec()).await.unwrap_err();
 
         // Try simple read
         assert_eq!("foobar", file_a.read_string().await?);
@@ -1293,7 +1315,7 @@ mod tests {
         let path = testdir.join("myfile");
         let tmp_path = testdir.join("myfile.tmp");
 
-        VirtualFile::crashsafe_overwrite(&path, &tmp_path, b"foo")
+        VirtualFile::crashsafe_overwrite(&path, &tmp_path, b"foo".to_vec())
             .await
             .unwrap();
         let mut file = MaybeVirtualFile::from(VirtualFile::open(&path).await.unwrap());
@@ -1302,7 +1324,7 @@ mod tests {
         assert!(!tmp_path.exists());
         drop(file);
 
-        VirtualFile::crashsafe_overwrite(&path, &tmp_path, b"bar")
+        VirtualFile::crashsafe_overwrite(&path, &tmp_path, b"bar".to_vec())
             .await
             .unwrap();
         let mut file = MaybeVirtualFile::from(VirtualFile::open(&path).await.unwrap());
@@ -1324,7 +1346,7 @@ mod tests {
         std::fs::write(&tmp_path, "some preexisting junk that should be removed").unwrap();
         assert!(tmp_path.exists());
 
-        VirtualFile::crashsafe_overwrite(&path, &tmp_path, b"foo")
+        VirtualFile::crashsafe_overwrite(&path, &tmp_path, b"foo".to_vec())
             .await
             .unwrap();