[PATCH] ext4: Improve feature checking
Sean Anderson
seanga2 at gmail.com
Mon Jul 1 02:32:48 CEST 2024
On 6/30/24 20:23, Sean Anderson wrote:
> On 6/30/24 17:25, Richard Weinberger wrote:
>> Evaluate the filesystem incompat and ro_compat bit fields to judge
>> whether the filesystem can be read or written.
>> For the read side only a scary warning is shown so far.
>> I'd love to about mounting too, but I fear this will break some setups
>
> I think you are missing a verb in the first half of your sentence
>
>> where the driver works by chance.
>>
>> Signed-off-by: Richard Weinberger <richard at nod.at>
>> ---
>> After facing ext4 write corruptions and read errors I checked
>> the ext4 implementation briefly.
>> Hopefully this patch helps other users to detect earlier that
>> they're using ext4 features which are not supported by u-boot.
>>
>> To make feature checking possible I had to figure what this
>> implementation actually supports.
>> I hope I got them right, feedback is welcome!
>>
>> Thanks,
>> //richard
>> ---
>> fs/ext4/ext4_common.c | 8 +++++++
>> fs/ext4/ext4_write.c | 12 ++++++++--
>> include/ext4fs.h | 55 ++++++++++++++++++++++++++++++++++++++++++-
>> 3 files changed, 72 insertions(+), 3 deletions(-)
>>
>> diff --git a/fs/ext4/ext4_common.c b/fs/ext4/ext4_common.c
>> index 2ff0dca249..7148d35ee0 100644
>> --- a/fs/ext4/ext4_common.c
>> +++ b/fs/ext4/ext4_common.c
>> @@ -2386,6 +2386,14 @@ int ext4fs_mount(void)
>> fs->inodesz = 128;
>> fs->gdsize = 32;
>> } else {
>> + int missing = __le32_to_cpu(data->sblock.feature_incompat) & \
>> + ~(EXT4_FEATURE_INCOMPAT_SUPP | \
>> + EXT4_FEATURE_INCOMPAT_SUPP_LAZY_RO);
>> +
>> + if (missing)
>> + log_err("fs uses incompatible features: %08x, failures *are* expected!\n",
>> + missing);
>> +
>
> I think it is a bit unclear to the user what their action should be. Maybe something like
>
> printf("EXT4 incompatible features: %08x, ignoring...\n")
>
> and then maybe add a comment like what you have in the commit message.
or maybe even
printf("EXT4 incompatible features: %08x, mounting read-only...\n")
>> debug("EXT4 features COMPAT: %08x INCOMPAT: %08x RO_COMPAT: %08x\n",
>> __le32_to_cpu(data->sblock.feature_compatibility),
>> __le32_to_cpu(data->sblock.feature_incompat),
>> diff --git a/fs/ext4/ext4_write.c b/fs/ext4/ext4_write.c
>> index d057f6b5a7..4aae3c5f7f 100644
>> --- a/fs/ext4/ext4_write.c
>> +++ b/fs/ext4/ext4_write.c
>> @@ -869,6 +869,7 @@ int ext4fs_write(const char *fname, const char *buffer,
>> ALLOC_CACHE_ALIGN_BUFFER(char, filename, 256);
>> bool store_link_in_inode = false;
>> memset(filename, 0x00, 256);
>> + int missing_feat;
>> if (type != FILETYPE_REG && type != FILETYPE_SYMLINK)
>> return -1;
>> @@ -882,8 +883,15 @@ int ext4fs_write(const char *fname, const char *buffer,
>> return -1;
>> }
>> - if (le32_to_cpu(fs->sb->feature_ro_compat) & EXT4_FEATURE_RO_COMPAT_METADATA_CSUM) {
>> - printf("Unsupported feature metadata_csum found, not writing.\n");
>> + missing_feat = le32_to_cpu(fs->sb->feature_incompat) & ~EXT4_FEATURE_INCOMPAT_SUPP;
>> + if (missing_feat) {
>> + log_err("Unsupported features found %08x, not writing.\n", missing_feat);
>> + return -1;
>> + }
>> +
>> + missing_feat = le32_to_cpu(fs->sb->feature_ro_compat) & ~EXT4_FEATURE_RO_COMPAT_SUPP;
>> + if (missing_feat) {
>> + log_err("Unsupported RO compat features found %08x, not writing.\n", missing_feat);
>> return -1;
>> }
>> diff --git a/include/ext4fs.h b/include/ext4fs.h
>> index d96edfd057..01b66f469f 100644
>> --- a/include/ext4fs.h
>> +++ b/include/ext4fs.h
>> @@ -34,12 +34,65 @@ struct disk_partition;
>> #define EXT4_TOPDIR_FL 0x00020000 /* Top of directory hierarchies*/
>> #define EXT4_EXTENTS_FL 0x00080000 /* Inode uses extents */
>> #define EXT4_EXT_MAGIC 0xf30a
>> -#define EXT4_FEATURE_RO_COMPAT_GDT_CSUM 0x0010
>> +
>> +#define EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER 0x0001
>> +#define EXT4_FEATURE_RO_COMPAT_LARGE_FILE 0x0002
>> +#define EXT4_FEATURE_RO_COMPAT_BTREE_DIR 0x0004
>> +#define EXT4_FEATURE_RO_COMPAT_HUGE_FILE 0x0008
>> +#define EXT4_FEATURE_RO_COMPAT_GDT_CSUM 0x0010
>> +#define EXT4_FEATURE_RO_COMPAT_DIR_NLINK 0x0020
>> +#define EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE 0x0040
>> +#define EXT4_FEATURE_RO_COMPAT_QUOTA 0x0100
>> +#define EXT4_FEATURE_RO_COMPAT_BIGALLOC 0x0200
>> #define EXT4_FEATURE_RO_COMPAT_METADATA_CSUM 0x0400
>> +
>> +#define EXT4_FEATURE_INCOMPAT_FILETYPE 0x0002
>> +#define EXTE_FEATURE_INCOMPAT_RECOVER 0x0004
>> #define EXT4_FEATURE_INCOMPAT_EXTENTS 0x0040
>> #define EXT4_FEATURE_INCOMPAT_64BIT 0x0080
>> +#define EXT4_FEATURE_INCOMPAT_MMP 0x0100
>> +#define EXT4_FEATURE_INCOMPAT_FLEX_BG 0x0200
>> +#define EXT4_FEATURE_INCOMPAT_CSUM_SEED 0x2000
>> +#define EXT4_FEATURE_INCOMPAT_ENCRYPT 0x10000
>> +
>> #define EXT4_INDIRECT_BLOCKS 12
>> +/*
>> + * Incompat features supported by this implementation.
>> + */
>> +#define EXT4_FEATURE_INCOMPAT_SUPP ( EXT4_FEATURE_INCOMPAT_FILETYPE \
>> + | EXTE_FEATURE_INCOMPAT_RECOVER \
>
> EXT4
>
>> + | EXT4_FEATURE_INCOMPAT_EXTENTS \
>> + | EXT4_FEATURE_INCOMPAT_64BIT \
>> + | EXT4_FEATURE_INCOMPAT_FLEX_BG \
>> + )
>
> Operators should go at the end of the line. So like
>
> #define EXT4_FEATURE_INCOMPAT_SUPP (EXT4_FEATURE_INCOMPAT_FILETYPE | \
> EXT4_FEATURE_INCOMPAT_RECOVER | \
> EXT4_FEATURE_INCOMPAT_EXTENTS | \
> EXT4_FEATURE_INCOMPAT_64BIT | \
> EXT4_FEATURE_INCOMPAT_FLEX_BG)
>
>> +/*
>> + * Incompat features supported by this implementation only in a lazy
>> + * way, good enough for reading files.
>> + *
>> + * - Multi mount protection (mmp) is not supported, but for read-only
>> + * we get away with it.
>> + * - Same fore metadata_csum_seed and metadata_csum.
>
> nit: for
>
>> + * - The implementation has also no clue about fscrypt, but it can read
>> + * unencrypted files. Reading encrypted files will read garbage.
>> + */
>> +#define EXT4_FEATURE_INCOMPAT_SUPP_LAZY_RO ( EXT4_FEATURE_INCOMPAT_MMP \
>> + | EXT4_FEATURE_INCOMPAT_CSUM_SEED \
>> + | EXT4_FEATURE_INCOMPAT_ENCRYPT \
>> + )
>
> ditto
>
>> +/*
>> + * Read-only compat features we support.
>> + * If unknown ro compat features are detected, writing to the fs is denied.
>> + */
>> +#define EXT4_FEATURE_RO_COMPAT_SUPP ( EXT4_FEATURE_RO_COMPAT_SPARSE_SUPER \
>> + | EXT4_FEATURE_RO_COMPAT_LARGE_FILE \
>> + | EXT4_FEATURE_RO_COMPAT_HUGE_FILE \
>> + | EXT4_FEATURE_RO_COMPAT_DIR_NLINK \
>> + | EXT4_FEATURE_RO_COMPAT_EXTRA_ISIZE \
>> + )
>
> ditto
>
>> #define EXT4_BG_INODE_UNINIT 0x0001
>> #define EXT4_BG_BLOCK_UNINIT 0x0002
>> #define EXT4_BG_INODE_ZEROED 0x0004
>
> Anyway, the substance of this patch is good. Just needs a little cosmetic cleanup.
>
> --Sean
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