fix qemu exit on memory hotplug when allocation fails at prealloc time

When adding hostmem backend at runtime, QEMU might exit with error:
  "os_mem_prealloc: Insufficient free host memory pages available to allocate guest RAM"

It happens due to os_mem_prealloc() not handling errors gracefully.

Fix it by passing errp argument so that os_mem_prealloc() could
report error to callers and undo performed allocation when
os_mem_prealloc() fails.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Message-Id: <1469008443-72059-1-git-send-email-imammedo@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

1 files changed, 8 insertions, 2 deletions

diff --git a/exec.c b/exec.c
index 50e3ee2..8ffde75 100644
--- a/exec.c
+++ b/exec.c
@@ -1226,7 +1226,7 @@ static void *file_ram_alloc(RAMBlock *block,
     char *filename;
     char *sanitized_name;
     char *c;
-    void *area;
+    void *area = MAP_FAILED;
     int fd = -1;
     int64_t page_size;
 
@@ -1314,13 +1314,19 @@ static void *file_ram_alloc(RAMBlock *block,
     }
 
     if (mem_prealloc) {
-        os_mem_prealloc(fd, area, memory);
+        os_mem_prealloc(fd, area, memory, errp);
+        if (errp && *errp) {
+            goto error;
+        }
     }
 
     block->fd = fd;
     return area;
 
 error:
+    if (area != MAP_FAILED) {
+        qemu_ram_munmap(area, memory);
+    }
     if (unlink_on_error) {
         unlink(path);
     }