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-rw-r--r--hw/9pfs/9p-synth.c2
-rw-r--r--hw/9pfs/9p.c9
2 files changed, 11 insertions, 0 deletions
diff --git a/hw/9pfs/9p-synth.c b/hw/9pfs/9p-synth.c
index 7eb210ffa8..cec8c0eefc 100644
--- a/hw/9pfs/9p-synth.c
+++ b/hw/9pfs/9p-synth.c
@@ -541,6 +541,8 @@ static int synth_init(FsContext *ctx, Error **errp)
     QLIST_INIT(&synth_root.child);
     qemu_mutex_init(&synth_mutex);
 
+    ctx->export_flags |= V9FS_NO_PERF_WARN;
+
     /* Add "." and ".." entries for root */
     v9fs_add_dir_node(&synth_root, synth_root.attr->mode,
                       "..", synth_root.attr, synth_root.attr->inode);
diff --git a/hw/9pfs/9p.c b/hw/9pfs/9p.c
index 7bb994bbf2..741d222c3f 100644
--- a/hw/9pfs/9p.c
+++ b/hw/9pfs/9p.c
@@ -1353,6 +1353,15 @@ static void coroutine_fn v9fs_version(void *opaque)
         goto out;
     }
 
+    /* 8192 is the default msize of Linux clients */
+    if (s->msize <= 8192 && !(s->ctx.export_flags & V9FS_NO_PERF_WARN)) {
+        warn_report_once(
+            "9p: degraded performance: a reasonable high msize should be "
+            "chosen on client/guest side (chosen msize is <= 8192). See "
+            "https://wiki.qemu.org/Documentation/9psetup#msize for details."
+        );
+    }
+
 marshal:
     err = pdu_marshal(pdu, offset, "ds", s->msize, &version);
     if (err < 0) {