btrfs: add helper to describe block group flags

Factor out helper that describes block group flags from
describe_relocation. The result will not be longer than the given size.
Signed-off-by: Anand Jain <anand.jain@oracle.com>
Reviewed-by: David Sterba <dsterba@suse.com>
[ add comments ]
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/relocation.c

@@ -4185,37 +4185,13 @@ static struct reloc_control *alloc_reloc_control(void)
 static void describe_relocation(struct btrfs_fs_info *fs_info,
 				struct btrfs_block_group_cache *block_group)
 {
-	char buf[128];		/* prefixed by a '|' that'll be dropped */
-	u64 flags = block_group->flags;
+	char buf[128] = {'\0'};
 
-	/* Shouldn't happen */
-	if (!flags) {
-		strcpy(buf, "|NONE");
-	} else {
-		char *bp = buf;
-
-#define DESCRIBE_FLAG(f, d) \
-		if (flags & BTRFS_BLOCK_GROUP_##f) { \
-			bp += snprintf(bp, buf - bp + sizeof(buf), "|%s", d); \
-			flags &= ~BTRFS_BLOCK_GROUP_##f; \
-		}
-		DESCRIBE_FLAG(DATA,     "data");
-		DESCRIBE_FLAG(SYSTEM,   "system");
-		DESCRIBE_FLAG(METADATA, "metadata");
-		DESCRIBE_FLAG(RAID0,    "raid0");
-		DESCRIBE_FLAG(RAID1,    "raid1");
-		DESCRIBE_FLAG(DUP,      "dup");
-		DESCRIBE_FLAG(RAID10,   "raid10");
-		DESCRIBE_FLAG(RAID5,    "raid5");
-		DESCRIBE_FLAG(RAID6,    "raid6");
-		if (flags)
-			snprintf(bp, buf - bp + sizeof(buf), "|0x%llx", flags);
-#undef DESCRIBE_FLAG
-	}
+	btrfs_describe_block_groups(block_group->flags, buf, sizeof(buf));
 
 	btrfs_info(fs_info,
 		   "relocating block group %llu flags %s",
-		   block_group->key.objectid, buf + 1);
+		   block_group->key.objectid, buf);
 }
 
 /*

fs/btrfs/volumes.c

@@ -130,6 +130,60 @@ const char *get_raid_name(enum btrfs_raid_types type)
 	return btrfs_raid_array[type].raid_name;
 }
 
+/*
+ * Fill @buf with textual description of @bg_flags, no more than @size_buf
+ * bytes including terminating null byte.
+ */
+void btrfs_describe_block_groups(u64 bg_flags, char *buf, u32 size_buf)
+{
+	int i;
+	int ret;
+	char *bp = buf;
+	u64 flags = bg_flags;
+	u32 size_bp = size_buf;
+
+	if (!flags) {
+		strcpy(bp, "NONE");
+		return;
+	}
+
+#define DESCRIBE_FLAG(flag, desc)						\
+	do {								\
+		if (flags & (flag)) {					\
+			ret = snprintf(bp, size_bp, "%s|", (desc));	\
+			if (ret < 0 || ret >= size_bp)			\
+				goto out_overflow;			\
+			size_bp -= ret;					\
+			bp += ret;					\
+			flags &= ~(flag);				\
+		}							\
+	} while (0)
+
+	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_DATA, "data");
+	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_SYSTEM, "system");
+	DESCRIBE_FLAG(BTRFS_BLOCK_GROUP_METADATA, "metadata");
+
+	DESCRIBE_FLAG(BTRFS_AVAIL_ALLOC_BIT_SINGLE, "single");
+	for (i = 0; i < BTRFS_NR_RAID_TYPES; i++)
+		DESCRIBE_FLAG(btrfs_raid_array[i].bg_flag,
+			      btrfs_raid_array[i].raid_name);
+#undef DESCRIBE_FLAG
+
+	if (flags) {
+		ret = snprintf(bp, size_bp, "0x%llx|", flags);
+		size_bp -= ret;
+	}
+
+	if (size_bp < size_buf)
+		buf[size_buf - size_bp - 1] = '\0'; /* remove last | */
+
+	/*
+	 * The text is trimmed, it's up to the caller to provide sufficiently
+	 * large buffer
+	 */
+out_overflow:;
+}
+
 static int init_first_rw_device(struct btrfs_trans_handle *trans,
 				struct btrfs_fs_info *fs_info);
 static int btrfs_relocate_sys_chunks(struct btrfs_fs_info *fs_info);

fs/btrfs/volumes.h

@@ -438,6 +438,7 @@ int btrfs_init_new_device(struct btrfs_fs_info *fs_info, const char *path);
 int btrfs_balance(struct btrfs_fs_info *fs_info,
 		  struct btrfs_balance_control *bctl,
 		  struct btrfs_ioctl_balance_args *bargs);
+void btrfs_describe_block_groups(u64 flags, char *buf, u32 size_buf);
 int btrfs_resume_balance_async(struct btrfs_fs_info *fs_info);
 int btrfs_recover_balance(struct btrfs_fs_info *fs_info);
 int btrfs_pause_balance(struct btrfs_fs_info *fs_info);