http://bugzilla.opensuse.org/show_bug.cgi?id=1191954 Bug ID: 1191954 Summary: btrfs fiemap results are inconsistent compared to XFS Classification: openSUSE Product: openSUSE Tumbleweed Version: Current Hardware: Other OS: Other Status: NEW Severity: Minor Priority: P5 - None Component: Kernel Assignee: wqu@suse.com Reporter: ddiss@suse.com QA Contact: qa-bugs@suse.de CC: kernel-bugs@opensuse.org Found By: --- Blocker: --- This is perhaps just a request for clarification rather than an actual bug. The workload is performed by Dracut, when patched with dracut-cpio reflink support. All files are on the same Btrfs FS / mount: - clone files into staging area via "cp --reflink=auto" - create initramfs cpio archive by cloning files in staging area as copy_file_range() source, and initramfs img as destination - fsync and close initramfs - delete staging area (rm -rf) - call fiemap on initramfs and count shared extents The goal of fiemap is to check which initramfs extents are shared with the "cp --reflink=auto" sources, not the staging area. With the same initramfs source files, XFS provides consistent fiemap results showing identical shared vs exclusive extents across multiple runs. On Btrfs the shared vs exclusive extent ratio varies wildly, with shared extent count often being much higher than would be expected possible with the "cp --reflink" source. This leads me to believe that the shared extents are associated with the deleted staging area, or are miscalculated by the filesystem. Full reproducer is: install a default Btrfs tumbleweed root (no snapshots), install reflink-capable Dracut from https://download.opensuse.org/repositories/home:/dmdiss:/rust-15x-initcowfs/... and then rebuild initramfs with the following /etc/dracut.conf configuration: do_strip=no tmpdir=/boot INITRD_COMPRESS=cat enhanced_cpio=yes run dracut and then: xfs_io -c "fiemap -v" initramfs -- You are receiving this mail because: You are on the CC list for the bug.