[Qemu-devel] [PATCH] qemu-img: Add --backing-chain option to info command

[Stefan Hajnoczi]

The qemu-img info --backing-chain option enumerates the backing file
chain.  For example, for base.qcow2 <- snap1.qcow2 <- snap2.qcow2 the
output becomes:

  $ qemu-img info --backing-chain snap2.qcow2
  image: snap2.qcow2
  file format: qcow2
  virtual size: 100M (104857600 bytes)
  disk size: 196K
  cluster_size: 65536
  backing file: snap1.qcow2
  backing file format: qcow2

  image: snap1.qcow2
  file format: qcow2
  virtual size: 100M (104857600 bytes)
  disk size: 196K
  cluster_size: 65536
  backing file: base.qcow2
  backing file format: qcow2

  image: base.qcow2
  file format: qcow2
  virtual size: 100M (104857600 bytes)
  disk size: 136K
  cluster_size: 65536

Signed-off-by: Stefan Hajnoczi <address@hidden>
---
 qemu-img.c | 98 ++++++++++++++++++++++++++++++++++++++++++++++++--------------
 1 file changed, 76 insertions(+), 22 deletions(-)

diff --git a/qemu-img.c b/qemu-img.c
index f17f187..c717f3e 100644
--- a/qemu-img.c
+++ b/qemu-img.c
@@ -1249,7 +1249,10 @@ static void dump_human_image_info(ImageInfo *info)
     }
 }
 
-enum {OPTION_OUTPUT = 256};
+enum {
+    OPTION_OUTPUT = 256,
+    OPTION_BACKING_CHAIN = 257,
+};
 
 typedef enum OutputFormat {
     OFORMAT_JSON,
@@ -1260,7 +1263,9 @@ static int img_info(int argc, char **argv)
 {
     int c;
     OutputFormat output_format = OFORMAT_HUMAN;
-    const char *filename, *fmt, *output;
+    bool chain = false;
+    const char *output;
+    char *filename, *fmt;
     BlockDriverState *bs;
     ImageInfo *info;
 
@@ -1272,6 +1277,7 @@ static int img_info(int argc, char **argv)
             {"help", no_argument, 0, 'h'},
             {"format", required_argument, 0, 'f'},
             {"output", required_argument, 0, OPTION_OUTPUT},
+            {"backing-chain", no_argument, 0, OPTION_BACKING_CHAIN},
             {0, 0, 0, 0}
         };
         c = getopt_long(argc, argv, "f:h",
@@ -1285,17 +1291,20 @@ static int img_info(int argc, char **argv)
             help();
             break;
         case 'f':
-            fmt = optarg;
+            fmt = g_strdup(optarg);
             break;
         case OPTION_OUTPUT:
             output = optarg;
             break;
+        case OPTION_BACKING_CHAIN:
+            chain = true;
+            break;
         }
     }
     if (optind >= argc) {
         help();
     }
-    filename = argv[optind++];
+    filename = g_strdup(argv[optind++]);
 
     if (output && !strcmp(output, "json")) {
         output_format = OFORMAT_JSON;
@@ -1303,31 +1312,76 @@ static int img_info(int argc, char **argv)
         output_format = OFORMAT_HUMAN;
     } else if (output) {
         error_report("--output must be used with human or json as argument.");
-        return 1;
+        goto err;
     }
 
-    bs = bdrv_new_open(filename, fmt, BDRV_O_FLAGS | BDRV_O_NO_BACKING, false);
-    if (!bs) {
-        return 1;
+    if (chain && output_format == OFORMAT_JSON) {
+        printf("[\n");
     }
 
-    info = g_new0(ImageInfo, 1);
-    collect_image_info(bs, info, filename, fmt);
+    do {
+        bs = bdrv_new_open(filename, fmt, BDRV_O_FLAGS | BDRV_O_NO_BACKING,
+                           false);
+        if (!bs) {
+            goto err;
+        }
 
-    switch (output_format) {
-    case OFORMAT_HUMAN:
-        dump_human_image_info(info);
-        dump_snapshots(bs);
-        break;
-    case OFORMAT_JSON:
-        collect_snapshots(bs, info);
-        dump_json_image_info(info);
-        break;
-    }
+        info = g_new0(ImageInfo, 1);
+        collect_image_info(bs, info, filename, fmt);
 
-    qapi_free_ImageInfo(info);
-    bdrv_delete(bs);
+        switch (output_format) {
+        case OFORMAT_HUMAN:
+            dump_human_image_info(info);
+            dump_snapshots(bs);
+            break;
+        case OFORMAT_JSON:
+            collect_snapshots(bs, info);
+            dump_json_image_info(info);
+            break;
+        }
+
+        g_free(filename);
+        g_free(fmt);
+        filename = NULL;
+        fmt = NULL;
+
+        if (chain) {
+            if (info->has_full_backing_filename) {
+                filename = g_strdup(info->full_backing_filename);
+            } else if (info->has_backing_filename) {
+                filename = g_strdup(info->backing_filename);
+            }
+
+            if (filename && info->has_backing_filename_format) {
+                fmt = g_strdup(info->backing_filename_format);
+            }
+
+            /* Print delimiters between items */
+            if (filename) {
+                switch (output_format) {
+                case OFORMAT_HUMAN:
+                    printf("\n");
+                    break;
+                case OFORMAT_JSON:
+                    printf(",\n");
+                    break;
+                }
+            }
+        }
+
+        qapi_free_ImageInfo(info);
+        bdrv_delete(bs);
+    } while (filename);
+
+    if (chain && output_format == OFORMAT_JSON) {
+        printf("]\n");
+    }
     return 0;
+
+err:
+    g_free(filename);
+    g_free(fmt);
+    return 1;
 }
 
 #define SNAPSHOT_LIST   1
-- 
1.7.11.4