[Qemu-devel] [PATCH] qemu-img: sort block formats in help message

[Mike Day <ncmike@ncultra.org>]

The help message for qemu-img lists the supported block formats, of
which there are 27 as of version 2.0.50. The formats are printed in
the order of their driver's position in a linked list, which appears
random. This patch prints the formats in sorted order, making it
easier to read and to find a specific format in the list.

[Added suggestions from Fam Zheng <famz@redhat.com> to declare variables
at the top of the scope in help() and to omit explicit cast for void*
opaque.
--Stefan]

[Removed call to g_sequence_lookup because it breaks the build on
 machines with glib < 2.28.
--Mike]

Signed-off-by: Mike Day <ncmike@ncultra.org>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
---
 qemu-img.c | 25 ++++++++++++++++++++++---
 1 file changed, 22 insertions(+), 3 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index 96f4463..93e51d1 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -32,6 +32,7 @@
 #include "block/block_int.h"
 #include "block/qapi.h"
 #include <getopt.h>
+#include <glib.h>
 
 #define QEMU_IMG_VERSION "qemu-img version " QEMU_VERSION \
                           ", Copyright (c) 2004-2008 Fabrice Bellard\n"
@@ -55,9 +56,22 @@ typedef enum OutputFormat {
 #define BDRV_O_FLAGS BDRV_O_CACHE_WB
 #define BDRV_DEFAULT_CACHE "writeback"
 
-static void format_print(void *opaque, const char *name)
+static gint compare_data(gconstpointer a, gconstpointer b, gpointer user)
 {
-    printf(" %s", name);
+    return g_strcmp0(a, b);
+}
+
+static void print_format(gpointer data, gpointer user)
+{
+    printf(" %s", (char *)data);
+}
+
+static void add_format_to_seq(void *opaque, const char *fmt_name)
+{
+    GSequence *seq = opaque;
+
+    g_sequence_insert_sorted(seq, (gpointer)fmt_name,
+                             compare_data, NULL);
 }
 
 static void QEMU_NORETURN GCC_FMT_ATTR(1, 2) error_exit(const char *fmt, ...)
@@ -142,10 +156,15 @@ static void QEMU_NORETURN help(void)
            "  '-f' first image format\n"
            "  '-F' second image format\n"
            "  '-s' run in Strict mode - fail on different image size or sector allocation\n";
+    GSequence *seq;
 
     printf("%s\nSupported formats:", help_msg);
-    bdrv_iterate_format(format_print, NULL);
+    seq = g_sequence_new(NULL);
+    bdrv_iterate_format(add_format_to_seq, seq);
+    g_sequence_foreach(seq, print_format, NULL);
     printf("\n");
+    g_sequence_free(seq);
+
     exit(EXIT_SUCCESS);
 }
 
-- 
1.9.0