[Qemu-devel] [PATCH v4 01/10] block: Auto-generate node_names for each BDS entry

[Jeff Cody]

Currently, node_name is only filled in when done so explicitly by the
user.  If no node_name is specified, then the node name field is not
populated.

If node_names are automatically generated when not specified, that means
that all block job operations can be done by reference to the unique
node_name field.  This eliminates ambiguity in resolving filenames
(relative filenames, or file descriptors, symlinks, mounts, etc..) that
qemu currently needs to deal with.

If a node name is specified, then it will not be automatically
generated for that BDS entry.

If it is automatically generated, it will be prefaced with "__qemu##",
followed by 8 characters of a unique number, followed by 8 random
ASCII characters in the range of 'A-Z'.  Some sample generated node-name
strings:
    __qemu##00000000IAIYNXXR
    __qemu##00000002METXTRBQ
    __qemu##00000001FMBORDWG

The prefix is to aid in identifying it as a qemu-generated name, the
numeric portion is to guarantee uniqueness in a given qemu session, and
the random characters are to further avoid any accidental collisions
with user-specified node-names.

Reviewed-by: Eric Blake <address@hidden>
Signed-off-by: Jeff Cody <address@hidden>
---
 block.c | 16 +++++++++++++++-
 1 file changed, 15 insertions(+), 1 deletion(-)

diff --git a/block.c b/block.c
index 310ea89..9882d3f 100644
--- a/block.c
+++ b/block.c
@@ -842,12 +842,26 @@ static int bdrv_open_flags(BlockDriverState *bs, int 
flags)
     return open_flags;
 }
 
+#define GEN_NODE_NAME_PREFIX    "__qemu##"
+#define GEN_NODE_NAME_MAX_LEN   (sizeof(GEN_NODE_NAME_PREFIX) + 8 + 8)
 static void bdrv_assign_node_name(BlockDriverState *bs,
                                   const char *node_name,
                                   Error **errp)
 {
+    char gen_node_name[GEN_NODE_NAME_MAX_LEN];
+    static uint32_t counter; /* simple counter to guarantee uniqueness */
+
+    /* if node_name is NULL, auto-generate a node name */
     if (!node_name) {
-        return;
+        int len;
+        snprintf(gen_node_name, GEN_NODE_NAME_MAX_LEN,
+                 "%s%08x", GEN_NODE_NAME_PREFIX, counter++);
+        len = strlen(gen_node_name);
+        while (len < GEN_NODE_NAME_MAX_LEN - 1) {
+            gen_node_name[len++] = g_random_int_range('A', 'Z');
+        }
+        gen_node_name[GEN_NODE_NAME_MAX_LEN - 1] = '\0';
+        node_name = gen_node_name;
     }
 
     /* empty string node name is invalid */
-- 
1.9.3