Add missing long options and --help output.
Also add -b short option for --backing-chain, and remove
now-unused OPTION_BACKING_CHAIN.

While at it, remove unused option_index variable.

Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>
---
 qemu-img.c | 40 +++++++++++++++++++++++++++-------------
 1 file changed, 27 insertions(+), 13 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 911cdc159c..cc51da31cf 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -65,7 +65,6 @@ typedef struct img_cmd_t {
 
 enum {
     OPTION_OUTPUT = 256,
-    OPTION_BACKING_CHAIN = 257,
     OPTION_OBJECT = 258,
     OPTION_IMAGE_OPTS = 259,
     OPTION_PATTERN = 260,
@@ -3219,31 +3218,44 @@ static int img_info(const img_cmd_t *ccmd, int argc, char **argv)
 
     fmt = NULL;
     for(;;) {
-        int option_index = 0;
         static const struct option long_options[] = {
             {"help", no_argument, 0, 'h'},
             {"format", required_argument, 0, 'f'},
             {"output", required_argument, 0, OPTION_OUTPUT},
-            {"backing-chain", no_argument, 0, OPTION_BACKING_CHAIN},
+            {"backing-chain", no_argument, 0, 'b'},
             {"object", required_argument, 0, OPTION_OBJECT},
             {"image-opts", no_argument, 0, OPTION_IMAGE_OPTS},
             {"force-share", no_argument, 0, 'U'},
             {0, 0, 0, 0}
         };
-        c = getopt_long(argc, argv, ":f:hU",
-                        long_options, &option_index);
+        c = getopt_long(argc, argv, "f:hbU",
+                        long_options, NULL);
         if (c == -1) {
             break;
         }
         switch(c) {
-        case ':':
-            missing_argument(argv[optind - 1]);
-            break;
-        case '?':
-            unrecognized_option(argv[optind - 1]);
-            break;
         case 'h':
-            help();
+            cmd_help(ccmd,
+"[-f FMT | --image-opts] [-b] [-U] [--object OBJDEF]\n"
+"        [--output human|json] FILENAME\n"
+,
+"  -f, --format FMT\n"
+"     specify FILENAME image format explicitly\n"
+"  --image-opts\n"
+"     indicates that FILENAME is a complete image specification\n"
+"     instead of a file name (incompatible with --format)\n"
+"  -b, --backing-chain\n"
+"     display information about backing chaing\n"
+"  (in case the image is stacked\n"
+"  -U, --force-share\n"
+"     open image in shared mode for concurrent access\n"
+"  --object OBJDEF\n"
+"     QEMU user-creatable object (eg encryption key)\n"
+"  --output human|json\n"
+"     specify output format name (default human)\n"
+"  FILENAME\n"
+"     image file name (or specification with --image-opts)\n"
+);
             break;
         case 'f':
             fmt = optarg;
@@ -3254,7 +3266,7 @@ static int img_info(const img_cmd_t *ccmd, int argc, char **argv)
         case OPTION_OUTPUT:
             output_format = parse_output_format(argv[0], optarg);
             break;
-        case OPTION_BACKING_CHAIN:
+        case 'b':
             chain = true;
             break;
         case OPTION_OBJECT:
@@ -3263,6 +3275,8 @@ static int img_info(const img_cmd_t *ccmd, int argc, char **argv)
         case OPTION_IMAGE_OPTS:
             image_opts = true;
             break;
+        default:
+            tryhelp(argv[0]);
         }
     }
     if (optind != argc - 1) {
-- 
2.39.2