dump: simplify write_start_flat_header()

Currently, the function
- defines and populates an auto variable of type MakedumpfileHeader
- allocates and zeroes a buffer of size MAX_SIZE_MDF_HEADER (4096)
- copies the former into the latter (covering an initial portion of the
  latter)

Fill in the MakedumpfileHeader structure in its final place (the alignment
is OK because the structure lives at the address returned by g_malloc0()).

Approximately-suggested-by: Luiz Capitulino <lcapitulino@redhat.com>
Signed-off-by: Laszlo Ersek <lersek@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>

1 files changed, 9 insertions, 11 deletions

diff --git a/dump.c b/dump.c
index ac4505ec80..6dec8d2cf1 100644
--- a/dump.c
+++ b/dump.c
@@ -711,27 +711,25 @@ static int create_vmcore(DumpState *s)
 
 static int write_start_flat_header(int fd)
 {
-    uint8_t *buf;
-    MakedumpfileHeader mh;
+    MakedumpfileHeader *mh;
     int ret = 0;
 
-    memset(&mh, 0, sizeof(mh));
-    memcpy(mh.signature, MAKEDUMPFILE_SIGNATURE,
-           MIN(sizeof mh.signature, sizeof MAKEDUMPFILE_SIGNATURE));
+    QEMU_BUILD_BUG_ON(sizeof *mh > MAX_SIZE_MDF_HEADER);
+    mh = g_malloc0(MAX_SIZE_MDF_HEADER);
 
-    mh.type = cpu_to_be64(TYPE_FLAT_HEADER);
-    mh.version = cpu_to_be64(VERSION_FLAT_HEADER);
+    memcpy(mh->signature, MAKEDUMPFILE_SIGNATURE,
+           MIN(sizeof mh->signature, sizeof MAKEDUMPFILE_SIGNATURE));
 
-    buf = g_malloc0(MAX_SIZE_MDF_HEADER);
-    memcpy(buf, &mh, sizeof(mh));
+    mh->type = cpu_to_be64(TYPE_FLAT_HEADER);
+    mh->version = cpu_to_be64(VERSION_FLAT_HEADER);
 
     size_t written_size;
-    written_size = qemu_write_full(fd, buf, MAX_SIZE_MDF_HEADER);
+    written_size = qemu_write_full(fd, mh, MAX_SIZE_MDF_HEADER);
     if (written_size != MAX_SIZE_MDF_HEADER) {
         ret = -1;
     }
 
-    g_free(buf);
+    g_free(mh);
     return ret;
 }