[PATCH] ext4: Improve feature checking

[Richard Weinberger]

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
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);
+
 		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_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.
+ * - 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 \
+					   )
+
+/*
+ * 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 \
+				    )
+
 #define EXT4_BG_INODE_UNINIT		0x0001
 #define EXT4_BG_BLOCK_UNINIT		0x0002
 #define EXT4_BG_INODE_ZEROED		0x0004
-- 
2.35.3