On Fri, Jul 22, 2016 at 05:59:11PM -0400, Tom Rini wrote:
With e2fsprogs after 1.43 the 64bit and metadata_csum features are enabled by default. The metadata_csum feature changes how ext4_group_desc->bg_checksum is calculated, which would break write support. The 64bit feature however introduces changes such that it cannot be read by implementations that do not support it. Since we do not support this, we must not mount it.
Cc: Stephen Warren swarren@nvidia.com Cc: Simon Glass sjg@chromium.org Cc: Lukasz Majewski l.majewski@samsung.com Cc: Stefan Roese sr@denx.de Reported-by: Andrew Bradford andrew.bradford@kodakalaris.com Signed-off-by: Tom Rini trini@konsulko.com
This problem has been seen in the wild a few times and reported in many places. If you've also found this problem, and reported it, please feel free to reply with a Reported-by tag, patchwork will pick them up. Further, we should look at adding support for 64bit and metadata_csum features as they will be showing up a lot more often now, but that's also non-trivial. A graceful fail like this is better than users being unable to load their files and being very puzzled.
fs/ext4/ext4_common.c | 10 ++++++++++ include/ext4fs.h | 1 + 2 files changed, 11 insertions(+)
diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c index 40b798a..eb49fce 100644 --- a/fs/ext4/ext4_common.c +++ b/fs/ext4/ext4_common.c @@ -2229,6 +2229,16 @@ int ext4fs_mount(unsigned part_length) if (__le16_to_cpu(data->sblock.magic) != EXT2_MAGIC) goto fail;
- /*
* The 64bit feature was enabled when metadata_csum was enabled* and we do not support metadata_csum (and cannot reliably find* files when it is set. Refuse to mount.*/
OK, I wrote the comment before I wrote the commit message, which I wrote after re-reading https://ext4.wiki.kernel.org/index.php/Ext4_Disk_Layout. I got stuck on metadata_csum being the cause rather than 64bit being the true "we must not read" problem. I'll re-word the comment to: The 64bit feature was enabled and this changes a number of data structures such that we cannot find files. Refuse to mount.
- if (data->sblock.feature_incompat & EXT4_FEATURE_INCOMPAT_64BIT) {
printf("Unsupported feature found (64bit, possibly metadata_csum), not mounting\n");
And this to: Unsupported feature found: 64bit. Not mounting