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migration: ensure qemu_fflush() always writes full data amount 

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 <dgilbert@redhat.com>
Signed-off-by: Daniel P. Berrange <berrange@redhat.com>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Message-Id: <1461751518-12128-5-git-send-email-berrange@redhat.com>
Signed-off-by: Amit Shah <amit.shah@redhat.com>
This commit is contained in:
Daniel P. Berrange 2016-04-27 11:04:54 +01:00 committed by Amit Shah
parent a8ec4437cd
commit baf51e7739
2 changed files with 16 additions and 6 deletions
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6
include/migration/qemu-file.h
View File

@ -28,7 +28,8 @@
/* This function writes a chunk of data to a file at the given position. /* 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 * 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, typedef ssize_t (QEMUFilePutBufferFunc)(void *opaque, const uint8_t *buf,
int64_t pos, size_t size); int64_t pos, size_t size);
@ -54,7 +55,8 @@ typedef int (QEMUFileCloseFunc)(void *opaque);
typedef int (QEMUFileGetFD)(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, typedef ssize_t (QEMUFileWritevBufferFunc)(void *opaque, struct iovec *iov,
int iovcnt, int64_t pos); int iovcnt, int64_t pos);

16
migration/qemu-file.c
View File

@ -108,11 +108,13 @@ bool qemu_file_is_writable(QEMUFile *f)
* Flushes QEMUFile buffer * Flushes QEMUFile buffer
* *
* If there is writev_buffer QEMUFileOps it uses it otherwise uses * 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) void qemu_fflush(QEMUFile *f)
{ {
ssize_t ret = 0; ssize_t ret = 0;
ssize_t expect = 0;
if (!qemu_file_is_writable(f)) { if (!qemu_file_is_writable(f)) {
return; return;
@ -120,21 +122,27 @@ void qemu_fflush(QEMUFile *f)
if (f->ops->writev_buffer) { if (f->ops->writev_buffer) {
if (f->iovcnt > 0) { if (f->iovcnt > 0) {
expect = iov_size(f->iov, f->iovcnt);
ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos); ret = f->ops->writev_buffer(f->opaque, f->iov, f->iovcnt, f->pos);
} }
} else { } else {
if (f->buf_index > 0) { if (f->buf_index > 0) {
expect = f->buf_index;
ret = f->ops->put_buffer(f->opaque, f->buf, f->pos, f->buf_index); ret = f->ops->put_buffer(f->opaque, f->buf, f->pos, f->buf_index);
} }
} }
if (ret >= 0) { if (ret >= 0) {
f->pos += ret; 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->buf_index = 0;
f->iovcnt = 0; f->iovcnt = 0;
if (ret < 0) {
qemu_file_set_error(f, ret);
}
} }
void ram_control_before_iterate(QEMUFile *f, uint64_t flags) void ram_control_before_iterate(QEMUFile *f, uint64_t flags)