Re: [Libguestfs] [libnbd PATCH] info: Add support for new 'qemu-nbd -A' qemu:allocation-depth

[Eric Blake]

On 10/16/20 10:23 AM, Eric Blake wrote:
> A rather trivial decoding; we may enhance it further if qemu extends
> things to give an integer depth alongside its tri-state encoding.
> ---
> 
> I'll wait to push this to libnbd until the counterpart qemu patches
> land upstream, although it looks like I've got positive review.

Whoops, I accidentally pushed this before qemu stuff landed upstream,
and in the meantime, we changed our minds on what to expose over
qemu:allocation-depth to be a bare integer rather than a tri-state.
I'll push this followup (but this time, wait for the actual qemu patch
to land).  In fact, I should probably add test-suite coverage...


>From eba8734654e6fd340e18b3e07c3213ed1a0ab9e8 Mon Sep 17 00:00:00 2001
From: Eric Blake <eblake@redhat.com>
Date: Tue, 27 Oct 2020 10:27:25 -0500
Subject: [libnbd PATCH] info: Adjust to actual 'qemu-nbd -A' semantics

Review on the qemu list has led to an altered definition of what
'qemu:allocation-depth' should report: rather than a tri-state value,
it is an actual depth.  It's time to match what actually got committed
into qemu, which in turn means a slight refactoring to use a malloc'd
string for a description.

Fixes: 71455c021
---
 info/nbdinfo.c | 27 +++++++++++++++------------
 1 file changed, 15 insertions(+), 12 deletions(-)

diff --git a/info/nbdinfo.c b/info/nbdinfo.c
index 2b22f51..b152f28 100644
--- a/info/nbdinfo.c
+++ b/info/nbdinfo.c
@@ -767,28 +767,30 @@ get_content (struct nbd_handle *nbd, int64_t size)
 }

 /* Callback handling --map. */
-static const char *
+static char *
 extent_description (const char *metacontext, uint32_t type)
 {
+  char *ret;
+
   if (strcmp (metacontext, "base:allocation") == 0) {
     switch (type) {
-    case 0: return "allocated";
-    case 1: return "hole";
-    case 2: return "zero";
-    case 3: return "hole,zero";
+    case 0: return strdup ("allocated");
+    case 1: return strdup ("hole");
+    case 2: return strdup ("zero");
+    case 3: return strdup ("hole,zero");
     }
   }
   else if (strncmp (metacontext, "qemu:dirty-bitmap:", 18) == 0) {
     switch (type) {
-    case 0: return "clean";
-    case 1: return "dirty";
+    case 0: return strdup ("clean");
+    case 1: return strdup ("dirty");
     }
   }
   else if (strcmp (metacontext, "qemu:allocation-depth") == 0) {
-    switch (type & 3) {
-    case 0: return "unallocated";
-    case 1: return "local";
-    case 2: return "backing";
+    switch (type) {
+    case 0: return strdup ("unallocated");
+    case 1: return strdup ("local");
+    case 2: asprintf (&ret, "backing depth %d", type); return ret;
     }
   }

@@ -810,7 +812,7 @@ extent_callback (void *user_data, const char
*metacontext,

   /* Print the entries received. */
   for (i = 0; i < nr_entries; i += 2) {
-    const char *descr = extent_description (map, entries[i+1]);
+    char *descr = extent_description (map, entries[i+1]);

     if (!json_output) {
       fprintf (fp, "%10" PRIu64 "  "
@@ -837,6 +839,7 @@ extent_callback (void *user_data, const char
*metacontext,
       comma = true;
     }

+    free (descr);
     offset += entries[i];
   }

-- 
2.29.0



-- 
Eric Blake, Principal Software Engineer
Red Hat, Inc.           +1-919-301-3226
Virtualization:  qemu.org | libvirt.org