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Subject[PATCH v3 1/2] staging: erofs: add requirements field in superblock
Date
There are some backward incompatible features pending
for months, mainly due to on-disk format expensions.

However, we should ensure that it cannot be mounted with
old kernels. Otherwise, it will causes unexpected behaviors.

Fixes: ba2b77a82022 ("staging: erofs: add super block operations")
Cc: <stable@vger.kernel.org> # 4.19+
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
---
change log v3:
- record requirements in erofs_sb_info for runtime use as well;

change log v2:
- update printed message

drivers/staging/erofs/erofs_fs.h | 13 ++++++++++---
drivers/staging/erofs/internal.h | 2 ++
drivers/staging/erofs/super.c | 19 +++++++++++++++++++
3 files changed, 31 insertions(+), 3 deletions(-)

diff --git a/drivers/staging/erofs/erofs_fs.h b/drivers/staging/erofs/erofs_fs.h
index fa52898df006..8ddb2b3e7d39 100644
--- a/drivers/staging/erofs/erofs_fs.h
+++ b/drivers/staging/erofs/erofs_fs.h
@@ -17,10 +17,16 @@
#define EROFS_SUPER_MAGIC_V1 0xE0F5E1E2
#define EROFS_SUPER_OFFSET 1024

+/*
+ * Any bits that aren't in EROFS_ALL_REQUIREMENTS should be
+ * incompatible with this kernel version.
+ */
+#define EROFS_ALL_REQUIREMENTS 0
+
struct erofs_super_block {
/* 0 */__le32 magic; /* in the little endian */
/* 4 */__le32 checksum; /* crc32c(super_block) */
-/* 8 */__le32 features;
+/* 8 */__le32 features; /* (aka. feature_compat) */
/* 12 */__u8 blkszbits; /* support block_size == PAGE_SIZE only */
/* 13 */__u8 reserved;

@@ -34,9 +40,10 @@ struct erofs_super_block {
/* 44 */__le32 xattr_blkaddr;
/* 48 */__u8 uuid[16]; /* 128-bit uuid for volume */
/* 64 */__u8 volume_name[16]; /* volume name */
+/* 80 */__le32 requirements; /* (aka. feature_incompat) */

-/* 80 */__u8 reserved2[48]; /* 128 bytes */
-} __packed;
+/* 84 */__u8 reserved2[44];
+} __packed; /* 128 bytes */

/*
* erofs inode data mapping:
diff --git a/drivers/staging/erofs/internal.h b/drivers/staging/erofs/internal.h
index 911333cdeef4..fc732c86ecd8 100644
--- a/drivers/staging/erofs/internal.h
+++ b/drivers/staging/erofs/internal.h
@@ -115,6 +115,8 @@ struct erofs_sb_info {

u8 uuid[16]; /* 128-bit uuid for volume */
u8 volume_name[16]; /* volume name */
+ u32 requirements;
+
char *dev_name;

unsigned int mount_opt;
diff --git a/drivers/staging/erofs/super.c b/drivers/staging/erofs/super.c
index f580d4ef77a1..cadbcc11702a 100644
--- a/drivers/staging/erofs/super.c
+++ b/drivers/staging/erofs/super.c
@@ -71,6 +71,22 @@ static void free_inode(struct inode *inode)
kmem_cache_free(erofs_inode_cachep, vi);
}

+static bool check_layout_compatibility(struct super_block *sb,
+ struct erofs_super_block *layout)
+{
+ const unsigned int requirements = le32_to_cpu(layout->requirements);
+
+ EROFS_SB(sb)->requirements = requirements;
+
+ /* check if current kernel meets all mandatory requirements */
+ if (requirements & (~EROFS_ALL_REQUIREMENTS)) {
+ errln("unidentified requirements %x, please upgrade kernel version",
+ requirements & ~EROFS_ALL_REQUIREMENTS);
+ return false;
+ }
+ return true;
+}
+
static int superblock_read(struct super_block *sb)
{
struct erofs_sb_info *sbi;
@@ -104,6 +120,9 @@ static int superblock_read(struct super_block *sb)
goto out;
}

+ if (!check_layout_compatibility(sb, layout))
+ goto out;
+
sbi->blocks = le32_to_cpu(layout->blocks);
sbi->meta_blkaddr = le32_to_cpu(layout->meta_blkaddr);
#ifdef CONFIG_EROFS_FS_XATTR
--
2.17.1
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