On 7/22/20 3:53 AM, Richard W.M. Jones wrote:
On Tue, Jul 21, 2020 at 07:41:21PM -0500, Eric Blake wrote:
On 7/21/20 3:47 PM, Richard W.M. Jones wrote:
+++ b/server/plugins.c
@@ -278,12 +278,30 @@ plugin_preconnect (struct backend *b, int readonly)
}
static void *
-plugin_open (struct backend *b, int readonly)
+plugin_open (struct backend *b, int readonly, const char *exportname)
{
+ GET_CONN;
struct backend_plugin *p = container_of (b, struct backend_plugin, backend);
assert (p->plugin.open != NULL);
+ /* Save the exportname since the lifetime of the string passed in
+ * here is likely to be brief. In addition this provides a place
+ * for nbdkit_export_name to retrieve it if called from the plugin.
+ *
+ * In API V3 we propose to pass the exportname as an extra parameter
+ * to the (new) plugin.open and deprecate nbdkit_export_name for V3
+ * users. Even then we will still need to save it in the handle
+ * because of the lifetime issue.
+ */
+ if (conn->exportname == NULL) {
Can't we assert(!conn->exportname) at this point? After all, we
only ever call .open at most once per connection.
I don't think so - backend_reopen will call plugin_open a second time.
As a test I added assert (conn->exportname == NULL) before this line
and it crashed in tests/test-retry.sh.
Fair enough.
+ if (conn->exportname_from_set_meta_context &&
+ strcmp (conn->exportname_from_set_meta_context, exportname) != 0) {
+ debug ("newstyle negotiation: NBD_OPT_SET_META_CONTEXT export name \"%s\" ≠ final client
exportname \"%s\", so discarding the previous context",
Long line, and I don't know if we use UTF-8 in other debug messages
or should stick to straight ascii. Compilation may have a glitch if
compiled under a different locale than the end binary runs in, but
these days, it's uncommon to find someone running in a single-byte
locale instead of UTF-8.
I thought we might be using ‘’ quotes (as we do in libguestfs) but I
see that we don't. I think we should use Unicode characters more
where they are appropriate, but I'll break up this long line. I also
added a comment.
I see you used Unicode quoting when refactoring the nbd plugin recently,
but yeah, I agree we haven't been using it much yet. I'm not opposed to
Unicode in C strings, but just pointing out that it can reduce the set
of platforms where things work out of the box (although these days,
since we require working gcc or clang for __attribute__((cleanup)), not
using Unicode is unlikely). Switching existing code to use nicer
quoting would be a separate cleanup series.
@@ -148,7 +166,7 @@ ext2_prepare (struct nbdkit_next_ops *next_ops, void
*nxdata, void *handle,
struct ext2_inode inode;
int64_t r;
CLEANUP_FREE char *name = NULL;
- const char *fname = file ?: nbdkit_export_name ();
+ const char *fname = file ?: h->exportname;
Hmm - we already pass the same 'readonly' state to filter's
.prepare, but not to backend_prepare(), which has to reconstruct it.
Would it be easier to also change the signature of backend_prepare()
to take both the original readonly and exportname passed to
backend_open(), rather than making the filter have to save it off in
the filter? It looks like protocol-handshake.c is the only caller,
and still has everything in scope at the time.
Possibly, although this would be a seperate change.
As I replied in a later mail, no, it would not be easier.
--
Eric Blake, Principal Software Engineer
Red Hat, Inc. +1-919-301-3226
Virtualization: qemu.org | libvirt.org
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