erofs: use feature_incompat rather than requirements

As Christoph said [1], "This is only cosmetic, why
not stick to feature_compat and feature_incompat?"

In my thought, requirements means "incompatible"
instead of "feature" though.

[1] https://lore.kernel.org/r/20190902125109.GA9826@infradead.org/Reported-by: Christoph Hellwig <hch@infradead.org>
Signed-off-by: Gao Xiang <gaoxiang25@huawei.com>
Link: https://lore.kernel.org/r/20190904020912.63925-7-gaoxiang25@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

fs/erofs/decompressor.c

@@ -129,7 +129,8 @@ static int lz4_decompress(struct z_erofs_decompress_req *rq, u8 *out)
 	support_0padding = false;
 
 	/* decompression inplace is only safe when 0padding is enabled */
-	if (EROFS_SB(rq->sb)->requirements & EROFS_REQUIREMENT_LZ4_0PADDING) {
+	if (EROFS_SB(rq->sb)->feature_incompat &
+	    EROFS_FEATURE_INCOMPAT_LZ4_0PADDING) {
 		support_0padding = true;
 
 		while (!src[inputmargin & ~PAGE_MASK])

fs/erofs/erofs_fs.h

@@ -11,17 +11,17 @@
 #define EROFS_SUPER_OFFSET      1024
 
 /*
- * Any bits that aren't in EROFS_ALL_REQUIREMENTS should be
- * incompatible with this kernel version.
+ * Any bits that aren't in EROFS_ALL_FEATURE_INCOMPAT should
+ * be incompatible with this kernel version.
  */
-#define EROFS_REQUIREMENT_LZ4_0PADDING	0x00000001
-#define EROFS_ALL_REQUIREMENTS		EROFS_REQUIREMENT_LZ4_0PADDING
+#define EROFS_FEATURE_INCOMPAT_LZ4_0PADDING	0x00000001
+#define EROFS_ALL_FEATURE_INCOMPAT		EROFS_FEATURE_INCOMPAT_LZ4_0PADDING
 
 /* 128-byte erofs on-disk super block */
 struct erofs_super_block {
 	__le32 magic;           /* file system magic number */
 	__le32 checksum;        /* crc32c(super_block) */
-	__le32 features;        /* (aka. feature_compat) */
+	__le32 feature_compat;
 	__u8 blkszbits;         /* support block_size == PAGE_SIZE only */
 	__u8 reserved;
 
@@ -35,7 +35,7 @@ struct erofs_super_block {
 	__le32 xattr_blkaddr;	/* start block address of shared xattr area */
 	__u8 uuid[16];          /* 128-bit uuid for volume */
 	__u8 volume_name[16];   /* volume name */
-	__le32 requirements;    /* (aka. feature_incompat) */
+	__le32 feature_incompat;
 
 	__u8 reserved2[44];
 };

fs/erofs/internal.h

@@ -96,7 +96,7 @@ struct erofs_sb_info {
 
 	u8 uuid[16];                    /* 128-bit uuid for volume */
 	u8 volume_name[16];             /* volume name */
-	u32 requirements;
+	u32 feature_incompat;
 
 	unsigned int mount_opt;
 

fs/erofs/super.c

@@ -67,14 +67,14 @@ static void free_inode(struct inode *inode)
 static bool check_layout_compatibility(struct super_block *sb,
 				       struct erofs_super_block *layout)
 {
-	const unsigned int requirements = le32_to_cpu(layout->requirements);
+	const unsigned int feature = le32_to_cpu(layout->feature_incompat);
 
-	EROFS_SB(sb)->requirements = requirements;
+	EROFS_SB(sb)->feature_incompat = feature;
 
 	/* 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);
+	if (feature & (~EROFS_ALL_FEATURE_INCOMPAT)) {
+		errln("unidentified incompatible feature %x, please upgrade kernel version",
+		      feature & ~EROFS_ALL_FEATURE_INCOMPAT);
 		return false;
 	}
 	return true;