Add statfs implementation

Signed-off-by: Christian Hagemeier <chagem@amazon.com>

mountpoint-s3/src/fs.rs

@@ -107,6 +107,42 @@ pub struct DirectoryEntry {
     lookup: LookedUp,
 }
 
+#[derive(Debug)]
+/// Reply to a 'statfs' call
+pub struct StatFs {
+    /// Total number of blocks
+    pub total_blocks: u64,
+    /// Number of free blocks
+    pub free_blocks: u64,
+    /// Number of free blocks available to unprivileged user
+    pub available_blocks: u64,
+    /// Number of inodes in file system
+    pub total_inodes: u64,
+    /// Available inodes
+    pub free_inodes: u64,
+    /// Optimal transfer block size
+    pub block_size: u32,
+    /// Maximum name length
+    pub maximum_name_length: u32,
+    /// Fragement size
+    pub fragment_size: u32,
+}
+
+impl Default for StatFs {
+    fn default() -> Self {
+        Self {
+            total_blocks: 0,
+            free_blocks: 0,
+            available_blocks: 0,
+            total_inodes: 0,
+            free_inodes: 0,
+            block_size: 512,
+            maximum_name_length: 255,
+            fragment_size: 0,
+        }
+    }
+}
+
 impl<Client, Prefetcher> S3Filesystem<Client, Prefetcher>
 where
     Client: ObjectClient + Clone + Send + Sync + 'static,
@@ -789,6 +825,24 @@ where
         }
         Ok(self.superblock.unlink(&self.client, parent_ino, name).await?)
     }
+
+    pub async fn statfs(&self, _ino: InodeNo) -> Result<StatFs, Error> {
+        const FREE_BLOCKS: u64 = u64::MAX / 2;
+        const FREE_INODES: u64 = u64::MAX / 2;
+        // According to https://docs.aws.amazon.com/AmazonS3/latest/userguide/object-keys.html any S3 object name can be at most
+        // 1024 bytes.
+        const MAX_NAME_LENGTH: u32 = 1024;
+
+        let reply = StatFs {
+            free_blocks: FREE_BLOCKS,
+            available_blocks: FREE_BLOCKS,
+            free_inodes: FREE_INODES,
+            maximum_name_length: MAX_NAME_LENGTH,
+            total_blocks: FREE_BLOCKS,
+            ..Default::default()
+        };
+        Ok(reply)
+    }
 }
 
 #[cfg(test)]

mountpoint-s3/src/fuse.rs

@@ -14,7 +14,7 @@ use crate::prefetch::Prefetch;
 use fuser::ReplyXTimes;
 use fuser::{
     Filesystem, KernelConfig, ReplyAttr, ReplyBmap, ReplyCreate, ReplyData, ReplyEmpty, ReplyEntry, ReplyIoctl,
-    ReplyLock, ReplyLseek, ReplyOpen, ReplyWrite, ReplyXattr, Request, TimeOrNow,
+    ReplyLock, ReplyLseek, ReplyOpen, ReplyStatfs, ReplyWrite, ReplyXattr, Request, TimeOrNow,
 };
 
 pub mod session;
@@ -580,4 +580,21 @@ where
     fn getxtimes(&self, _req: &Request<'_>, ino: u64, reply: ReplyXTimes) {
         fuse_unsupported!("getxtimes", reply);
     }
+
+    #[instrument(level="warn", skip_all, fields(req=_req.unique(), ino=ino))]
+    fn statfs(&self, _req: &Request<'_>, ino: u64, reply: ReplyStatfs) {
+        match block_on(self.fs.statfs(ino).in_current_span()) {
+            Ok(statfs) => reply.statfs(
+                statfs.total_blocks,
+                statfs.free_blocks,
+                statfs.available_blocks,
+                statfs.total_inodes,
+                statfs.free_inodes,
+                statfs.block_size,
+                statfs.maximum_name_length,
+                statfs.fragment_size,
+            ),
+            Err(e) => fuse_error!("statfs", reply, e),
+        }
+    }
 }