The QEMUFile writev_buffer / put_buffer functions are expected
to write out the full set of requested data, blocking until
complete. The qemu_fflush() caller does not expect to deal with
partial writes. Clarify the function comments and add a sanity
check to the code to catch mistaken implementations.
Reviewed-by: Dr. David Alan Gilbert <dgilb...@redhat.com>
Signed-off-by: Daniel P. Berrange <berra...@redhat.com>
---
include/migration/qemu-file.h | 6 ++++--
migration/qemu-file.c | 16 ++++++++++++----
2 files changed, 16 insertions(+), 6 deletions(-)
diff --git a/include/migration/qemu-file.h b/include/migration/qemu-file.h
index 3f6b4ed..5909ff0 100644
--- a/include/migration/qemu-file.h
+++ b/include/migration/qemu-file.h
@@ -28,7 +28,8 @@
/* This function writes a chunk of data to a file at the given position.
* The pos argument can be ignored if the file is only being used for
- * streaming. The handler should try to write all of the data it can.
+ * streaming. The handler must write all of the data or return a negative
+ * errno value.
*/
typedef ssize_t (QEMUFilePutBufferFunc)(void *opaque, const uint8_t *buf,
int64_t pos, size_t size);
@@ -54,7 +55,8 @@ typedef int (QEMUFileCloseFunc)(void *opaque);
typedef int (QEMUFileGetFD)(void *opaque);
/*
- * This function writes an iovec to file.
+ * This function writes an iovec to file. The handler must write all
+ * of the data or return a negative errno value.
*/
typedef ssize_t (QEMUFileWritevBufferFunc)(void *opaque, struct iovec *iov,
int iovcnt, int64_t pos);
diff --git a/migration/qemu-file.c b/migration/qemu-file.c
index 6f4a129..656db4a 100644
--- a/migration/qemu-file.c
+++ b/migration/qemu-file.c
@@ -108,11 +108,13 @@ bool qemu_file_is_writable(QEMUFile *f)
* Flushes QEMUFile buffer
*
* If there is writev_buffer QEMUFileOps it uses it otherwise uses
- * put_buffer ops.
+ * put_buffer ops. This will flush all pending data. If data was
+ * only partially flushed, it will set an error state.
*/
void qemu_fflush(QEMUFile *f)
{
ssize_t ret = 0;
+ ssize_t expect = 0;
if (!qemu_file_is_writable(f)) {
return;
@@ -120,21 +122,27 @@ void qemu_fflush(QEMUFile *f)
if (f->ops->writev_buffer) {
if (f->iovcnt > 0) {
+ expect = iov_size(f->iov, f->iovcnt);
ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos);
}
} else {
if (f->buf_index > 0) {
+ expect = f->buf_index;
ret = f->ops->put_buffer(f->opaque, f->buf, f->pos, f->buf_index);
}
}
+
if (ret >= 0) {
f->pos += ret;
}
+ /* We expect the QEMUFile write impl to send the full
+ * data set we requested, so sanity check that.
+ */
+ if (ret != expect) {
+ qemu_file_set_error(f, ret < 0 ? ret : -EIO);
+ }
f->buf_index = 0;
f->iovcnt = 0;
- if (ret < 0) {
- qemu_file_set_error(f, ret);
- }
}
void ram_control_before_iterate(QEMUFile *f, uint64_t flags)
--
2.5.0
