backport https://gitlab.com/qemu-project/qemu/-/commit/37d10da
From 37d10da587d5d241520c502706192da5806cc370 Mon Sep 17 00:00:00 2001
From: Peter Lieven <pl@dlhnet.de>
Date: Fri, 6 Mar 2026 14:28:40 +0000
Subject: [PATCH] block/nfs: add support for libnfs v6

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>
Message-ID: <20260306142840.72923-1-pl@dlhnet.de>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
---
 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 f45885f05a..bb0d1d993a 100644
--- a/meson.build
+++ b/meson.build
@@ -1157,7 +1157,7 @@ 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
-- 
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