[Qemu-devel] [PATCH 4/5] qemu-file: Fix qemu_put_compression_data flaw

[Liang Li <liang.z.li@intel.com>]

Current qemu_put_compression_data can only work with no writable
QEMUFile, and can't work with the writable QEMUFile. But it does
not provide any measure to prevent users from using it with a
writable QEMUFile.

We should fix this flaw to make it works with writable QEMUFile.

Suggested-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Liang Li <liang.z.li@intel.com>
---
 migration/qemu-file.c | 23 +++++++++++++++++++++--
 migration/ram.c       |  6 +++++-
 2 files changed, 26 insertions(+), 3 deletions(-)

diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 6f4a129..b0ef1f3 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -607,8 +607,14 @@ uint64_t qemu_get_be64(QEMUFile *f)
     return v;
 }
 
-/* compress size bytes of data start at p with specific compression
+/* Compress size bytes of data start at p with specific compression
  * level and store the compressed data to the buffer of f.
+ *
+ * When f is not writable, return -1 if f has no space to save the
+ * compressed data.
+ * When f is wirtable and it has no space to save the compressed data,
+ * do fflush first, if f still has no space to save the compressed
+ * data, return -1.
  */
 
 ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
@@ -617,7 +623,14 @@ ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
     ssize_t blen = IO_BUF_SIZE - f->buf_index - sizeof(int32_t);
 
     if (blen < compressBound(size)) {
-        return 0;
+        if (!qemu_file_is_writable(f)) {
+            return -1;
+        }
+        qemu_fflush(f);
+        blen = IO_BUF_SIZE - sizeof(int32_t);
+        if (blen < compressBound(size)) {
+            return -1;
+        }
     }
     if (compress2(f->buf + f->buf_index + sizeof(int32_t), (uLongf *)&blen,
                   (Bytef *)p, size, level) != Z_OK) {
@@ -625,7 +638,13 @@ ssize_t qemu_put_compression_data(QEMUFile *f, const uint8_t *p, size_t size,
         return 0;
     }
     qemu_put_be32(f, blen);
+    if (f->ops->writev_buffer) {
+        add_to_iovec(f, f->buf + f->buf_index, blen);
+    }
     f->buf_index += blen;
+    if (f->buf_index == IO_BUF_SIZE) {
+        qemu_fflush(f);
+    }
     return blen + sizeof(int32_t);
 }
 
diff --git a/migration/ram.c b/migration/ram.c
index bc34bc5..7e62d8d 100644
--- a/migration/ram.c
+++ b/migration/ram.c
@@ -821,7 +821,11 @@ static int do_compress_ram_page(CompressParam *param)
                                   RAM_SAVE_FLAG_COMPRESS_PAGE);
     blen = qemu_put_compression_data(param->file, p, TARGET_PAGE_SIZE,
                                      migrate_compress_level());
-    bytes_sent += blen;
+    if (blen < 0) {
+        error_report("Insufficient buffer for compressed data!");
+    } else {
+        bytes_sent += blen;
+    }
 
     return bytes_sent;
 }
-- 
1.9.1