Re: [Libguestfs] [nbdkit PATCH 1/2] retry: Add in retry support during .open

Now that a filter can open a backend as many times as it wants, there's no longer a technical reason we can't retry .open. However, adding retry logic here does mean we have to weaken an assert in the server backend code, since prepare can now be reached more than once. Test coverage will be added in a separate patch, so that it becomes easy to swap patch order and see that the test fails without this patch. See also https://bugzilla.redhat.com/show_bug.cgi?id=1841820 ---

+static void * +retry_open (nbdkit_next_open *next, nbdkit_context *nxdata, + int readonly, const char *exportname, int is_tls) +{ + struct retry_handle *h; + struct retry_data data = {0}; + + h = malloc (sizeof *h);

+ if (h == NULL) { + nbdkit_error ("malloc: %m"); + return NULL; + } + + h->readonly = readonly; + h->exportname = strdup (exportname); + h->context = nxdata; + if (h->exportname == NULL) { + nbdkit_error ("strdup: %m"); + free (h); + return NULL; + } + h->reopens = 0; + + if (next (nxdata, readonly, exportname) != -1) + h->open = true; + else {

+ /* Careful - our .open must not return a handle unless do_retry() + * works, as the caller's next action will be calling .get_size + * and similar probe functions which we do not bother to wire up + * into retry logic because they only need to be used right after + * connecting. + */ + nbdkit_next *next_handle = NULL; + int err = ESHUTDOWN; + + while (! h->open && do_retry (h, &data, &next_handle, "open", &err))