Commit a5242d37c8 ("erofs: error out obviously illegal extents in
advance") changed the per-extent algorithm presence check from "is the
bit set" to "is the only bit set":
- !(sbi->available_compr_algs & (1 << map->m_algorithmformat))
+ (sbi->available_compr_algs ^ BIT(map->m_algorithmformat))
`available_compr_algs` is a bitmap of every compression algorithm
available in the image (z_erofs_parse_cfgs() iterates it with
for_each_set_bit()), so an image that enables more than one algorithm
has multiple bits set. XOR is zero only when the bitmap is exactly
BIT(map->m_algorithmformat); for any image with two or more algorithms
the test is non-zero for every extent and the read fails with
-EFSCORRUPTED ("inconsistent algorithmtype %u").
Reproducer (mkfs.erofs from erofs-utils 1.7.1):
$ mkdir src
$ yes A | head -c 100K > src/a
$ head -c 64K /dev/zero > src/b
$ mkfs.erofs -zlz4:deflate multi.erofs src
$ mount -t erofs -o loop multi.erofs /mnt
$ cat /mnt/a >/dev/null
cat: /mnt/a: Structure needs cleaning
$ dmesg | tail
erofs (device loop0): inconsistent algorithmtype 0 for nid 46
erofs (device loop0): read error -117 @ 0 of nid 46
The erofs on-disk format (Z_EROFS_COMPRESSION_MAX = 4 with LZ4, LZMA,
DEFLATE, ZSTD) and the kernel parser explicitly support
multi-algorithm images, and erofs-utils 1.7.1 generates them via the
"-z X:Y" syntax.
Restore the original per-bit presence check.
Fixes: a5242d37c8 ("erofs: error out obviously illegal extents in advance")
Signed-off-by: Zhan Xusheng <zhanxusheng@xiaomi.com>
Reviewed-by: Gao Xiang <hsiangkao@linux.alibaba.com>
Signed-off-by: Gao Xiang <hsiangkao@linux.alibaba.com>
27f2d085bd