From: Christian Taedcke christian.taedcke@weidmueller.com
This series fixes an issue where the FAT type (FAT12, FAT16) is not correctly detected, e.g. when the BPB field BS_FilSysType contains the valid value "FAT ".
This issue occures, for example, if a partition is formatted by swupdate using its diskformat handler. swupdate uses the FAT library from http://elm-chan.org/fsw/ff/ internally.
See https://groups.google.com/g/swupdate/c/7Yc3NupjXx8 for a discussion in the swupdate mailing list.
Please refer to the commit messages for more details.
1. Added bootsector checks
Most tests from https://www.win.tue.nl/~aeb/linux/fs/fat/fat-2.html are added in the latest commit. Only the tests VIII, IX and X are not implemented.
I also checked the Linux kernel code (v6.6) and did not find any checks on 'vistart->fs_type'. This is the reason why is skipped them here.
See section '3. Size comparisons' for the impact on the binary size.
2. Tests
I will try to implement some tests for the next version of this series.
3. Size comparisons
I executed bloat-o-meter from the Linux kernel for an arm64 target (config xilinx_zynqmp_mini_emmc0_defconfig):
Comparison of the binary spl/u-boot-spl between master (rev e17d174773e9ba9447596708e702b7382e47a6cf) and this patch series (including the added validity checks of the boot sector):
add/remove: 0/0 grow/shrink: 1/1 up/down: 100/-12 (88) Function old new delta read_bootsectandvi 308 408 +100 fat_itr_root 444 432 -12 Total: Before=67977, After=68065, chg +0.13%
When compare the size of the binary spl/u-boot-spl between master this series without the the validity checks of the boot sector (so i removed the last commit in this series):
add/remove: 0/0 grow/shrink: 0/2 up/down: 0/-24 (-24) Function old new delta read_bootsectandvi 308 296 -12 fat_itr_root 444 432 -12 Total: Before=67977, After=67953, chg -0.04%
So the size of the spl on this arm64 target increases by 88 bytes for this series. When i remove the validity check the size decreases by 24 bytes.
Changes in v2: - Use get_unaligned_le16 instead of custom macro - Move code change in test/image/spl_load_fs.c into separate commit - Use get_unaligned_le16 instead of custom macro - Extract FAT32 logic from determine_fat_bits() into read_bootsectandvi() - Rename determine_fat_bits() to determine_legacy_fat_bits() - Keep one goto label instead of removing both - Move changing gotos from read_bootsectandvi() into separate commit - Add validity checks for boot sector
Christian Taedcke (5): fs: fat: use get_unaligned_le16 to convert u8[2] to u16 test: spl: Remove usage of FAT32_SIGN fs: fat: calculate FAT type based on cluster count fs: fat: simplify gotos from read_bootsectandvi fs: fat: add bootsector validity check
fs/fat/fat.c | 114 +++++++++++++++++++++++++++++---------- include/fat.h | 6 --- test/image/spl_load_fs.c | 2 +- 3 files changed, 88 insertions(+), 34 deletions(-)