[PATCH 1/1] util/memfd: allow allocating 0 bytes

[donno2048]

This silently fixes issues resulting from trying to allocate 0 bytes.

Fixes error, for example, for writing byte 0x20 to port 0x3c0, then word 0xf09 
to port 0x3b4 when CPU is initiated, which shouldn't break.

Signed-off-by: donno2048 <just4now666...@gmail.com>
---
 util/memfd.c | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/util/memfd.c b/util/memfd.c
index 07beab174d..4f2c4ea1dd 100644
--- a/util/memfd.c
+++ b/util/memfd.c
@@ -131,9 +131,13 @@ void *qemu_memfd_alloc(const char *name, size_t size, 
unsigned int seals,
         }
     }
 
-    ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
-    if (ptr == MAP_FAILED) {
-        goto err;
+    if (size != 0) {
+        ptr = mmap(0, size, PROT_READ | PROT_WRITE, MAP_SHARED, mfd, 0);
+        if (ptr == MAP_FAILED) {
+            goto err;
+        }
+    } else {
+        ptr = fdopen(mfd, "rw");
     }
 
     *fd = mfd;
-- 
2.30.2