[vlc-devel] Libnfs API changed

[ronnie sahlberg]

Libnfs is now pushing out a new major release.
This wll affect VLC as some signatures in the API has changed in order
to allow zero-copy for the READ paths.
This greatly improves performance on low=end devices such as RPi.

The new API is mainly due to nfs_read* cha ngin its signature to make
zero-copy possible.
But since this breaks pretty much every application, why not clean up
and fix all other warts in the API at the same time.

VLC as dar as I can tell only uses the high-level APIs so the changes
should be fairly trivial.
This is an example on how fio added compile time support for either
the classic api or the new api:

---
diff --git a/engines/nfs.c b/engines/nfs.c
index 6bc4af1f..13b55038 100644
--- a/engines/nfs.c
+++ b/engines/nfs.c
@@ -157,16 +157,28 @@ static int queue_write(struct fio_libnfs_options
*o, struct io_u *io_u)
 {
        struct nfs_data *nfs_data = io_u->engine_data;

+#ifdef LIBNFS_API_V2
+       return nfs_pwrite_async(o->context, nfs_data->nfsfh,
+                               io_u->buf, io_u->buflen, io_u->offset,
+                               nfs_callback, io_u);
+#else
        return nfs_pwrite_async(o->context, nfs_data->nfsfh, io_u->offset,
                                io_u->buflen, io_u->buf, nfs_callback, io_u);
+#endif
 }

 static int queue_read(struct fio_libnfs_options *o, struct io_u *io_u)
 {
        struct nfs_data *nfs_data = io_u->engine_data;

+#ifdef LIBNFS_API_V2
+       return nfs_pread_async(o->context, nfs_data->nfsfh,
+                               io_u->buf, io_u->buflen, io_u->offset,
+                               nfs_callback, io_u);
+#else
        return nfs_pread_async(o->context, nfs_data->nfsfh, io_u->offset,
                                io_u->buflen, nfs_callback, io_u);
+#endif
 }
--


VLC will need the same type of ifdef conditionals to ensure it can
compile against either API.

It is painful to break an API but sometimes you have to. And there is
no difference between breaking it a little and breaking it alot so
taking the opportunity to fix a lot of mistakes done in the last 20
years.

In exchange for this breakage I offer significantly improved
performance on very low end devices with poor memory bandwidth. Likem
the original RPi.

regards
ronnie sahlberg