Re: [Libguestfs] [nbdkit PATCH 1/2] blocksize: Refactor to per-handle constraints

An upcoming patch wants to make the blocksize filter more responsive to the actual .block_size limits from the underlying plugin. But those limits can differ per export (for example, qemu can export multiple images, where one backed by a file has minblock 1, but another backed by encryption has minblock 512). To do that, we need to track block size constraints per handle, rather than globally. At this point, no functional change is intended; the change is merely the refactoring to get per-handle values, and deferring the settling of defaults not specified during .config to now be initialized during .prepare rather than .config_complete. The next patch can then modify .block_size to actually honor the underlying plugin constraints. --- I wrote this patch by temporarily renaming the globals min_block and so on, to let the compiler flag where we want to use the h->minblock per-handle variant. If we want to leave the globals named slightly differently for safety, let me know, and I can reinstate that.

@@ -114,28 +122,20 @@ blocksize_config_complete (nbdkit_next_config_complete *next, return -1; } } - else - minblock = 1; - if (maxdata) { + if (maxdata && minblock) { if (maxdata & (minblock - 1)) { nbdkit_error ("maxdata must be a multiple of %u", minblock); return -1; } } - else if (maxlen) - maxdata = MIN (maxlen, 64 * 1024 * 1024); - else - maxdata = 64 * 1024 * 1024; - if (maxlen) { + if (maxlen && minblock) { if (maxlen & (minblock - 1)) { nbdkit_error ("maxlen must be a multiple of %u", minblock); return -1; } } - else - maxlen = -minblock;

return next (nxdata); } @@ -145,16 +145,66 @@ blocksize_config_complete (nbdkit_next_config_complete *next, "maxdata=<SIZE> Maximum size for read/write (default 64M).\n" \ "maxlen=<SIZE> Maximum size for trim/zero (default 4G-minblock)." +static void * +blocksize_open (nbdkit_next_open *next, nbdkit_context *nxdata, + int readonly, const char *exportname, int is_tls) +{ + struct blocksize_handle *h; + + if (next (nxdata, readonly, exportname) == -1) + return NULL; + + h = malloc (sizeof *h); + if (h == NULL) { + nbdkit_error ("malloc: %m"); + return NULL; + } + + h->minblock = minblock; + h->maxdata = maxdata; + h->maxlen = maxlen; + return h; +} + +static int +blocksize_prepare (nbdkit_next *next, void *handle, + int readonly) +{ + struct blocksize_handle *h = handle; + + if (h->minblock == 0) + h->minblock = 1; + if (h->maxdata == 0) { + if (h->maxlen) + h->maxdata = MIN (h->maxlen, 64 * 1024 * 1024); + else + h->maxdata = 64 * 1024 * 1024; + } + if (h->maxlen == 0) + h->maxlen = -h->minblock; + + return 0; +}

+ + +static void +blocksize_close (void *handle)