Re: [Libguestfs] [nbdkit PATCH] plugins: Use static buffer for plugin_zeroes

No need to calloc/free a buffer every time NBD_CMD_WRITE_ZEROES has to fall back to a .pread call. Just reserve the maximum buffer up front in our bss. Signed-off-by: Eric Blake <eblake(a)redhat.com&gt; --- I noticed that buf was a candidate for CLEANUP_FREE, but then further noticed that we can avoid the calloc/free altogether if we don't mind the bss being 64M larger. server/plugins.c | 10 ++-------- 1 file changed, 2 insertions(+), 8 deletions(-) diff --git a/server/plugins.c b/server/plugins.c index 947bb6d..acdfa1f 100644 --- a/server/plugins.c +++ b/server/plugins.c @@ -594,7 +594,7 @@ plugin_zero (struct backend *b, struct connection *conn, uint32_t count, uint64_t offset, uint32_t flags, int *err) { struct backend_plugin *p = container_of (b, struct backend_plugin, backend); - char *buf; + static const char buf[MAX_REQUEST_SIZE]; uint32_t limit; int r = -1; bool may_trim = flags & NBDKIT_FLAG_MAY_TRIM; @@ -639,12 +639,7 @@ plugin_zero (struct backend *b, struct connection *conn, assert (p->plugin.pwrite || p->plugin._pwrite_old); flags &= ~NBDKIT_FLAG_MAY_TRIM; threadlocal_set_error (0); - limit = count < MAX_REQUEST_SIZE ? count : MAX_REQUEST_SIZE; - buf = calloc (limit, 1); - if (!buf) { - *err = ENOMEM; - return -1; - } + limit = count < sizeof (buf) ? count : sizeof (buf); while (count) { r = plugin_pwrite (b, conn, buf, limit, offset, flags, err); @@ -656,7 +651,6 @@ plugin_zero (struct backend *b, struct connection *conn, } *err = errno; - free (buf); errno = *err; done: --