patch "staging: erofs: add requirements field in superblock" added to staging-next

[<gregkh@linuxfoundation.org>]

This is a note to let you know that I've just added the patch titled

    staging: erofs: add requirements field in superblock

to my staging git tree which can be found at
    git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
in the staging-next branch.

The patch will show up in the next release of the linux-next tree
(usually sometime within the next 24 hours during the week.)

The patch will also be merged in the next major kernel release
during the merge window.

If you have any questions about this process, please let me know.


From 5efe5137f05bbb4688890620934538c005e7d1d6 Mon Sep 17 00:00:00 2001
From: Gao Xiang <gaoxiang25@huawei.com>
Date: Thu, 13 Jun 2019 16:35:41 +0800
Subject: staging: erofs: add requirements field in superblock

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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
 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 c47778b3fabd..382258fc124d 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
-- 
2.22.0