6:17 a.m.
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