[Libguestfs] [PATCH nbdkit] server: Pass the export name through filter .open calls.

[Eric Blake]

On 7/21/20 7:41 PM, Eric Blake wrote:

>> @@ -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.

Nope, we can't.  It's because the sequence is:

backend_open("clientname")
   outer_filter.open("clientname")
     next_open("outername")
       inner_filter.open("outername")
         next_open("innername")
           plugin.open("innername")
backend_prepare()
   backend_prepare()
     backend_prepare()
       plugin.prepare()
     inner_filter.prepare()
   outer_filter.prepare()

while protocol-handshake.c has the same "clientname" to pass to both 
backend_open() and backend_prepare(), the outer-to-inner order of .open 
is (intentionally) opposite the inner-to-outer order of .prepare, and 
the name passed to plugin.open has indeed left scope.  Unless we want 
backend.c to start storing the name passed into backend_open().

> 
>> +++ b/filters/log/log.c
>> @@ -227,11 +227,12 @@ output_return (struct handle *h, const char 
>> *act, uint64_t id, int r, int *err)
>>   /* Open a connection. */
>>   static void *
>> -log_open (nbdkit_next_open *next, void *nxdata, int readonly)
>> +log_open (nbdkit_next_open *next, void *nxdata,
>> +          int readonly, const char *exportname)
>>   {
>>     struct handle *h;
>> -  if (next (nxdata, readonly) == -1)
>> +  if (next (nxdata, readonly, exportname) == -1)
>>       return NULL;
> 
> Pre-existing - the log filter should include the exportname somewhere in 
> its output log.  Well, nothing like the present to fix it ;)

I did that in the meantime, so you'll need a slight rebase.

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