From c44151867fd1f4c6afc93403158473a9dd023141 Mon Sep 17 00:00:00 2001
From: Jonathan Klimt <jonathan.klimt@eonerc.rwth-aachen.de>
Date: Fri, 12 Sep 2025 22:39:18 +0200
Subject: [PATCH] lseek: Fixed incorrect lseek behaviour with whence Set or Cur

---
 src/fs/fuse.rs | 51 ++++++++++++++++++++++++++++++++++----------------
 1 file changed, 35 insertions(+), 16 deletions(-)

diff --git a/src/fs/fuse.rs b/src/fs/fuse.rs
index 065b0cb414..cab0b9ae5c 100644
--- a/src/fs/fuse.rs
+++ b/src/fs/fuse.rs
@@ -724,25 +724,44 @@ impl FuseFileHandleInner {
 	}
 
 	fn lseek(&mut self, offset: isize, whence: SeekWhence) -> io::Result<isize> {
-		debug!("FUSE lseek");
+		debug!("FUSE lseek: offset: {offset}, whence: {whence:?}");
+
+		// Seek on fuse file systems seems to be a little odd: All reads are referenced from the
+		// beginning of the file, thus we have to track the offset ourself. Also, a read doesn't
+		// move the read pointer on the remote side, so we can't get the current position using
+		// remote lseek when referencing from `Cur` and we have to use the internally tracked
+		// position instead.
+		match whence {
+			SeekWhence::End | SeekWhence::Data | SeekWhence::Hole => {
+				if let (Some(nid), Some(fh)) = (self.fuse_nid, self.fuse_fh) {
+					let (cmd, rsp_payload_len) = ops::Lseek::create(nid, fh, offset, whence);
+					let rsp = get_filesystem_driver()
+						.ok_or(Errno::Nosys)?
+						.lock()
+						.send_command(cmd, rsp_payload_len)?;
+
+					if rsp.headers.out_header.error < 0 {
+						return Err(Errno::Io);
+					}
 
-		if let (Some(nid), Some(fh)) = (self.fuse_nid, self.fuse_fh) {
-			let (cmd, rsp_payload_len) = ops::Lseek::create(nid, fh, offset, whence);
-			let rsp = get_filesystem_driver()
-				.ok_or(Errno::Nosys)?
-				.lock()
-				.send_command(cmd, rsp_payload_len)?;
+					let rsp_offset = rsp.headers.op_header.offset;
+					self.offset = rsp.headers.op_header.offset.try_into().unwrap();
 
-			if rsp.headers.out_header.error < 0 {
-				return Err(Errno::Io);
+					Ok(rsp_offset.try_into().unwrap())
+				} else {
+					Err(Errno::Io)
+				}
+			}
+			SeekWhence::Set => {
+				self.offset = offset.try_into().map_err(|_e| Errno::Inval)?;
+				Ok(self.offset as isize)
+			}
+			SeekWhence::Cur => {
+				self.offset = (self.offset as isize + offset)
+					.try_into()
+					.map_err(|_e| Errno::Inval)?;
+				Ok(self.offset as isize)
 			}
-
-			let rsp_offset = rsp.headers.op_header.offset;
-			self.offset = rsp.headers.op_header.offset.try_into().unwrap();
-
-			Ok(rsp_offset.try_into().unwrap())
-		} else {
-			Err(Errno::Io)
 		}
 	}