From 91c91c1632d7296ced443e7f1ae1903e027d82e6 Mon Sep 17 00:00:00 2001
From: David Sterba <dsterba@suse.com>
Date: Tue, 5 Oct 2021 14:05:04 +0200
Subject: [PATCH] btrfs-progs: sb-mod: improve help

Print the list of supported members to change and explain what the tool
does.

Signed-off-by: David Sterba <dsterba@suse.com>
---
 btrfs-sb-mod.c | 34 ++++++++++++++++++++++++++++++----
 1 file changed, 30 insertions(+), 4 deletions(-)

diff --git a/btrfs-sb-mod.c b/btrfs-sb-mod.c
index 6dde98b2..f56388bd 100644
--- a/btrfs-sb-mod.c
+++ b/btrfs-sb-mod.c
@@ -215,6 +215,18 @@ static bool op_is_write(enum field_op op)
 	return op != OP_GET;
 }
 
+static const char * const type_to_string(enum field_type type)
+{
+	switch (type) {
+	case TYPE_U8:	return "u8";
+	case TYPE_U16:	return "u16";
+	case TYPE_U32:	return "u32";
+	case TYPE_U64:	return "u64";
+	case TYPE_UNKNOWN:
+	}
+	return "UNKNOWN";
+}
+
 static void mod_field_by_name(struct btrfs_super_block *sb, int set, const char *name,
 		u64 *val)
 {
@@ -329,10 +341,15 @@ int main(int argc, char **argv)
 
 	memset(spec, 0, sizeof(spec));
 	if (argc <= 2) {
-		printf("Usage: %s image [fieldspec...]\n", argv[0]);
-		printf("Where fileldspec is: member op\n");
-		printf("  member: name of the superblock member\n");
-		printf("  op: single character optionally followed by a value\n");
+		printf("Usage: %s [options] image [fieldspec...]\n", argv[0]);
+		printf("\n");
+		printf("Modify or read a a member of the primary superblock on a given image (file or block device),\n");
+		printf("checksum is recalculated after any modification (ie. it is not when just reading the values).\n");
+		printf("Use 'btrfs inspect dump-super image' to read the whole superblock\n");
+		printf("\n");
+		printf("fileldspec is a sequence of pairs 'member op':\n");
+		printf("  member: name of the superblock member, listed below\n");
+		printf("  op: single character optionally followed by a value (eg. =0x42)\n");
 		printf("    . read the member value (no value)\n");
 		printf("    ? read the member value (no value)\n");
 		printf("    = set member to the exact value (value required)\n");
@@ -340,6 +357,15 @@ int main(int argc, char **argv)
 		printf("    - subtract this value from member (value required)\n");
 		printf("    ^ xor member with this value (value required)\n");
 		printf("    @ byteswap of the member (no value)\n");
+		printf("\n");
+		printf("  member (type)\n");
+
+		for (i = 0; i < ARRAY_SIZE(known_fields); i++) {
+			const int width = 24;
+
+			printf("    %-*s  %s\n", width, known_fields[i].name,
+					type_to_string(known_fields[i].type));
+		}
 		exit(1);
 	}
 	fd = open(argv[1], O_RDWR | O_EXCL);