libnfs v6 added a new api structure for read and write requests.

This effectively also adds zero copy read support for cases where
the qiov coming from the block layer has only one vector.

The .brdv_refresh_limits implementation is needed because libnfs v6
silently dropped support for splitting large read/write request into
chunks.

Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
Signed-off-by: Peter Lieven <pl@dlhnet.de>
---
 block/nfs.c | 50 +++++++++++++++++++++++++++++++++++++++++++++++++-
 meson.build |  2 +-
 2 files changed, 50 insertions(+), 2 deletions(-)

diff --git a/block/nfs.c b/block/nfs.c
index b78f4f86e8..53e267fa75 100644
--- a/block/nfs.c
+++ b/block/nfs.c
@@ -69,7 +69,9 @@ typedef struct NFSClient {
 typedef struct NFSRPC {
     BlockDriverState *bs;
     int ret;
+#ifndef LIBNFS_API_V2
     QEMUIOVector *iov;
+#endif
     struct stat *st;
     Coroutine *co;
     NFSClient *client;
@@ -237,6 +239,7 @@ nfs_co_generic_cb(int ret, struct nfs_context *nfs, void *data,
     NFSRPC *task = private_data;
     task->ret = ret;
     assert(!task->st);
+#ifndef LIBNFS_API_V2
     if (task->ret > 0 && task->iov) {
         if (task->ret <= task->iov->size) {
             qemu_iovec_from_buf(task->iov, 0, data, task->ret);
@@ -244,6 +247,7 @@ nfs_co_generic_cb(int ret, struct nfs_context *nfs, void *data,
             task->ret = -EIO;
         }
     }
+#endif
     if (task->ret < 0) {
         error_report("NFS Error: %s", nfs_get_error(nfs));
     }
@@ -266,13 +270,36 @@ static int coroutine_fn nfs_co_preadv(BlockDriverState *bs, int64_t offset,
 {
     NFSClient *client = bs->opaque;
     NFSRPC task;
+    char *buf = NULL;
+    bool my_buffer = false;
 
     nfs_co_init_task(bs, &task);
-    task.iov = iov;
+
+#ifdef LIBNFS_API_V2
+    if (iov->niov != 1) {
+        buf = g_try_malloc(bytes);
+        if (bytes && buf == NULL) {
+            return -ENOMEM;
+        }
+        my_buffer = true;
+    } else {
+        buf = iov->iov[0].iov_base;
+    }
+#endif
 
     WITH_QEMU_LOCK_GUARD(&client->mutex) {
+#ifdef LIBNFS_API_V2
+        if (nfs_pread_async(client->context, client->fh,
+                            buf, bytes, offset,
+                            nfs_co_generic_cb, &task) != 0) {
+#else
+        task.iov = iov;
         if (nfs_pread_async(client->context, client->fh,
                             offset, bytes, nfs_co_generic_cb, &task) != 0) {
+#endif
+            if (my_buffer) {
+                g_free(buf);
+            }
             return -ENOMEM;
         }
 
@@ -280,6 +307,13 @@ static int coroutine_fn nfs_co_preadv(BlockDriverState *bs, int64_t offset,
     }
     qemu_coroutine_yield();
 
+    if (my_buffer) {
+        if (task.ret > 0) {
+            qemu_iovec_from_buf(iov, 0, buf, task.ret);
+        }
+        g_free(buf);
+    }
+
     if (task.ret < 0) {
         return task.ret;
     }
@@ -315,9 +349,15 @@ static int coroutine_fn nfs_co_pwritev(BlockDriverState *bs, int64_t offset,
     }
 
     WITH_QEMU_LOCK_GUARD(&client->mutex) {
+#ifdef LIBNFS_API_V2
+        if (nfs_pwrite_async(client->context, client->fh,
+                             buf, bytes, offset,
+                             nfs_co_generic_cb, &task) != 0) {
+#else
         if (nfs_pwrite_async(client->context, client->fh,
                              offset, bytes, buf,
                              nfs_co_generic_cb, &task) != 0) {
+#endif
             if (my_buffer) {
                 g_free(buf);
             }
@@ -856,6 +896,13 @@ static void coroutine_fn nfs_co_invalidate_cache(BlockDriverState *bs,
 }
 #endif
 
+static void nfs_refresh_limits(BlockDriverState *bs, Error **errp)
+{
+    NFSClient *client = bs->opaque;
+    bs->bl.max_transfer = MIN((uint32_t)nfs_get_readmax(client->context),
+                              (uint32_t)nfs_get_writemax(client->context));
+}
+
 static const char *nfs_strong_runtime_opts[] = {
     "path",
     "user",
@@ -893,6 +940,7 @@ static BlockDriver bdrv_nfs = {
     .bdrv_detach_aio_context        = nfs_detach_aio_context,
     .bdrv_attach_aio_context        = nfs_attach_aio_context,
     .bdrv_refresh_filename          = nfs_refresh_filename,
+    .bdrv_refresh_limits            = nfs_refresh_limits,
     .bdrv_dirname                   = nfs_dirname,
 
     .strong_runtime_opts            = nfs_strong_runtime_opts,
diff --git a/meson.build b/meson.build
index df841e12e2..3bb78c0788 100644
--- a/meson.build
+++ b/meson.build
@@ -1156,7 +1156,7 @@ endif
 
 libnfs = not_found
 if not get_option('libnfs').auto() or have_block
-  libnfs = dependency('libnfs', version: ['>=1.9.3', '<6.0.0'],
+  libnfs = dependency('libnfs', version: '>=1.9.3',
                       required: get_option('libnfs'),
                       method: 'pkg-config')
 endif
-- 
2.47.3

Am 06.03.2026 um 15:28 hat Peter Lieven geschrieben:
> libnfs v6 added a new api structure for read and write requests.
> 
> This effectively also adds zero copy read support for cases where
> the qiov coming from the block layer has only one vector.
> 
> The .brdv_refresh_limits implementation is needed because libnfs v6
> silently dropped support for splitting large read/write request into
> chunks.
> 
> Signed-off-by: Ronnie Sahlberg <ronniesahlberg@gmail.com>
> Signed-off-by: Peter Lieven <pl@dlhnet.de>

Thanks, applied to the block branch.

> @@ -280,6 +307,13 @@ static int coroutine_fn nfs_co_preadv(BlockDriverState *bs, int64_t offset,
>      }
>      qemu_coroutine_yield();
>  
> +    if (my_buffer) {
> +        if (task.ret > 0) {
> +            qemu_iovec_from_buf(iov, 0, buf, task.ret);
> +        }
> +        g_free(buf);
> +    }

I wonder if it wouldn't be easier to just always do the copy in the
callback. The only thing that would need to be version dependent is the
buffer that contains the actual data (the @data parameter in
nfs_co_generic_cb or the bounce buffer).

But I assume we'll touch this code again soon enough, because I saw that
libnfs recently added vectored reads. If we can use them, that would be
even more efficient. (But somehow it didn't add vectored writes at the
same time? Strange.)

Kevin