[Libguestfs] [libnbd PATCH v2 6/6] info: Tolerate missing size

[Eric Blake]

As previous patches showed, the NBD spec does not yet forbid a server
sending us a size that does not fit in int64_t.  We should gracefully
handle this during nbdinfo, rather than giving up early.

With the same one-line hack to qemu to set the most significant bit of
the export size, output changes from pre-patch:

$ ./run nbdinfo nbd://localhost
/home/eblake/libnbd/info/.libs/nbdinfo: nbd_get_size: server claims size 9223372036854781440 which does not fit in signed result: Value too large for defined data type
qemu-nbd: option negotiation failed: Failed to read opts magic: Unexpected end-of-file before all data were read

to post-patch:

$ ./run nbdinfo nbd://localhost
protocol: newstyle-fixed without TLS, using extended packets
...
	block_size_maximum: 33554432

or

$ ./run nbdinfo nbd://localhost --json
{
"protocol": "newstyle-fixed",
...
	"block_size_maximum": 33554432,
	"export-size-str": "unavailable"
	} ]
}

Sadly, since writing a server with such large export sizes requires a
one-off hack, I don't see the point in adding a unit test.

Signed-off-by: Eric Blake <eblake at redhat.com>
---
 info/show.c | 25 +++++++++++++------------
 1 file changed, 13 insertions(+), 12 deletions(-)

diff --git a/info/show.c b/info/show.c
index a71d837e..3d80545e 100644
--- a/info/show.c
+++ b/info/show.c
@@ -46,7 +46,7 @@ show_one_export (struct nbd_handle *nbd, const char *desc,
                  bool first, bool last)
 {
   int64_t i, size;
-  char size_str[HUMAN_SIZE_LONGEST];
+  char size_str[HUMAN_SIZE_LONGEST] = "unavailable";
   bool human_size_flag;
   char *export_name = NULL;
   char *export_desc = NULL;
@@ -89,13 +89,10 @@ show_one_export (struct nbd_handle *nbd, const char *desc,
     return false;
   }
   size = nbd_get_size (nbd);
-  if (size == -1) {
-    fprintf (stderr, "%s: %s\n", progname, nbd_get_error ());
-    exit (EXIT_FAILURE);
+  if (size >= 0) {
+    human_size (size_str, size, &human_size_flag);
   }

-  human_size (size_str, size, &human_size_flag);
-
   if (uri_is_meaningful ())
     uri = nbd_get_uri (nbd);

@@ -130,7 +127,8 @@ show_one_export (struct nbd_handle *nbd, const char *desc,
     show_context = true;

   /* Get content last, as it moves the connection out of negotiating */
-  content = get_content (nbd, size);
+  if (size >= 0)
+    content = get_content (nbd, size);

   if (!json_output) {
     ansi_colour (ANSI_FG_BOLD_BLACK, fp);
@@ -140,10 +138,12 @@ show_one_export (struct nbd_handle *nbd, const char *desc,
     fprintf (fp, ":\n");
     if (desc && *desc)
       fprintf (fp, "\tdescription: %s\n", desc);
-    if (human_size_flag)
-      fprintf (fp, "\texport-size: %" PRIi64 " (%s)\n", size, size_str);
-    else
-      fprintf (fp, "\texport-size: %" PRIi64 "\n", size);
+    if (size >= 0) {
+      if (human_size_flag)
+        fprintf (fp, "\texport-size: %" PRIi64 " (%s)\n", size, size_str);
+      else
+        fprintf (fp, "\texport-size: %" PRIi64 "\n", size);
+    }
     if (content)
       fprintf (fp, "\tcontent: %s\n", content);
     if (uri)
@@ -273,7 +273,8 @@ show_one_export (struct nbd_handle *nbd, const char *desc,
                block_maximum);

     /* Put this one at the end because of the stupid comma thing in JSON. */
-    fprintf (fp, "\t\"export-size\": %" PRIi64 ",\n", size);
+    if (size >= 0)
+      fprintf (fp, "\t\"export-size\": %" PRIi64 ",\n", size);
     fprintf (fp, "\t\"export-size-str\": \"%s\"\n", size_str);

     if (last)
-- 
2.41.0