exec: add parameter errp to gethugepagesize

Add parameter errp to gethugepagesize thus callers can handle errors.

If user adds a memory-backend-file object using object_add command,
specifying a non-existing directory for property mem-path, qemu will
core dump with message:

  /nonexistingdir: No such file or directory
  Bad ram offset fffffffffffff000
  Aborted (core dumped)

This patch fixes the problem. With this patch, qemu reports an error
message like:

  qemu-system-x86_64: -object memory-backend-file,mem-path=/nonexistingdir,id=mem-file0,size=128M:
  failed to get page size of file /nonexistingdir: No such file or directory

Signed-off-by: Hu Tao <hutao@cn.fujitsu.com>
Reviewed-by: Peter Crosthwaite <peter.crosthwaite@xilinx.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

exec.c

diff --git a/exec.c b/exec.c
index 1100208..dd1e576 100644
--- a/exec.c
+++ b/exec.c
@@ -1031,7 +1031,7 @@
 
 #define HUGETLBFS_MAGIC       0x958458f6
 
-static long gethugepagesize(const char *path)
+static long gethugepagesize(const char *path, Error **errp)
 {
     struct statfs fs;
     int ret;
@@ -1041,7 +1041,8 @@
     } while (ret != 0 && errno == EINTR);
 
     if (ret != 0) {
-        perror(path);
+        error_setg_errno(errp, errno, "failed to get page size of file %s",
+                         path);
         return 0;
     }
 
@@ -1062,9 +1063,11 @@
     void *area = NULL;
     int fd;
     uint64_t hpagesize;
+    Error *local_err = NULL;
 
-    hpagesize = gethugepagesize(path);
-    if (!hpagesize) {
+    hpagesize = gethugepagesize(path, &local_err);
+    if (local_err) {
+        error_propagate(errp, local_err);
         goto error;
     }