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The GRUB btrfs implementation can't handle two very basic btrfs file layouts: 1. Mixed inline/regualr extents # mkfs.btrfs -f test.img # mount test.img /mnt/btrfs # xfs_io -f -c "pwrite 0 1k" -c "sync" -c "falloc 0 4k" \ -c "pwrite 4k 4k" /mnt/btrfs/file # umount /mnt/btrfs # ./grub-fstest ./grub-fstest --debug=btrfs ~/test.img hex "/file" Such mixed inline/regular extents case is not recommended layout, but all existing tools and kernel can handle it without problem. 2. NO_HOLES feature # mkfs.btrfs -f test.img -O no_holes # mount test.img /mnt/btrfs # xfs_io -f -c "pwrite 0 4k" -c "pwrite 8k 4k" /mnt/btrfs/file # umount /mnt/btrfs # ./grub-fstest ./grub-fstest --debug=btrfs ~/test.img hex "/file" NO_HOLES feature is going to be the default mkfs feature in the incoming v5.15 release, and kernel has support for it since v4.0. The way GRUB btrfs code iterates through file extents relies on no gap between extents. If any gap is hit, then GRUB btrfs will error out, without any proper reason to help debug the bug. This is a bad assumption, since a long long time ago btrfs has a new feature called NO_HOLES to allow btrfs to skip the padding hole extent to reduce metadata usage. The NO_HOLES feature is already stable since kernel v4.0 and is going to be the default mkfs feature in the incoming v5.15 btrfs-progs release. When there is a extent gap, instead of error out, just try next item. This is still not ideal, as kernel/progs/U-boot all do the iteration item by item, not relying on the file offset continuity. But it will be way more time consuming to correct the whole behavior than starting from scratch to build a proper designed btrfs module for GRUB. Signed-off-by: Qu Wenruo <wqu@suse.com> Reviewed-by: Daniel Kiper <daniel.kiper@oracle.com>
This is GRUB 2, the second version of the GRand Unified Bootloader. GRUB 2 is rewritten from scratch to make GNU GRUB cleaner, safer, more robust, more powerful, and more portable. See the file NEWS for a description of recent changes to GRUB 2. See the file INSTALL for instructions on how to build and install the GRUB 2 data and program files. See the file MAINTAINERS for information about the GRUB maintainers, etc. If you found a security vulnerability in the GRUB please check the SECURITY file to get more information how to properly report this kind of bugs to the maintainers. Please visit the official web page of GRUB 2, for more information. The URL is <http://www.gnu.org/software/grub/grub.html>. More extensive documentation is available in the Info manual, accessible using 'info grub' after building and installing GRUB 2. There are a number of important user-visible differences from the first version of GRUB, now known as GRUB Legacy. For a summary, please see: info grub Introduction 'Changes from GRUB Legacy'