Introduce a buffered file wrapper for QEMUFile

This patch introduces a buffered QEMUFile wrapper.  This allows QEMUFile's to be
rate limited.  It also makes it easier to implement a QEMUFile that is
asynchronous since the current QEMUFile API requires that all reads and writes
be synchronous.

The only real non-obvious part of the API is the "frozen" concept.  If the
backend returns EAGAIN, the QEMUFile is said to be "frozen".  This means no
additional output will be sent to the backend until the file is unfrozen.
qemu_file_put_notify can be used to unfreeze a frozen file.

A synchronous interface is also provided to wait for an unfreeze event.  This is
used during the final part of live migration when the VM is no longer running.

Signed-off-by: Anthony Liguori <aliguori@us.ibm.com>



git-svn-id: svn://svn.savannah.nongnu.org/qemu/trunk@5475 c046a42c-6fe2-441c-8c8c-71466251a162

1 files changed, 250 insertions, 0 deletions

diff --git a/buffered_file.c b/buffered_file.c
new file mode 100644
index 0000000..1d72b46
--- /dev/null
+++ b/buffered_file.c
@@ -0,0 +1,250 @@
+/*
+ * QEMU buffered QEMUFile
+ *
+ * Copyright IBM, Corp. 2008
+ *
+ * Authors:
+ *  Anthony Liguori   <aliguori@us.ibm.com>
+ *
+ * This work is licensed under the terms of the GNU GPL, version 2.  See
+ * the COPYING file in the top-level directory.
+ *
+ */
+
+#include "qemu-common.h"
+#include "hw/hw.h"
+#include "qemu-timer.h"
+#include "sysemu.h"
+#include "qemu-char.h"
+#include "buffered_file.h"
+
+//#define DEBUG_BUFFERED_FILE
+
+typedef struct QEMUFileBuffered
+{
+    BufferedPutFunc *put_buffer;
+    BufferedPutReadyFunc *put_ready;
+    BufferedWaitForUnfreezeFunc *wait_for_unfreeze;
+    BufferedCloseFunc *close;
+    void *opaque;
+    QEMUFile *file;
+    int has_error;
+    int freeze_output;
+    size_t bytes_xfer;
+    size_t xfer_limit;
+    uint8_t *buffer;
+    size_t buffer_size;
+    size_t buffer_capacity;
+    QEMUTimer *timer;
+} QEMUFileBuffered;
+
+#ifdef DEBUG_BUFFERED_FILE
+#define dprintf(fmt, ...) \
+    do { printf("buffered-file: " fmt, ## __VA_ARGS__); } while (0)
+#else
+#define dprintf(fmt, ...) \
+    do { } while (0)
+#endif
+
+static void buffered_append(QEMUFileBuffered *s,
+                            const uint8_t *buf, size_t size)
+{
+    if (size > (s->buffer_capacity - s->buffer_size)) {
+        void *tmp;
+
+        dprintf("increasing buffer capacity from %ld by %ld\n",
+                s->buffer_capacity, size + 1024);
+
+        s->buffer_capacity += size + 1024;
+
+        tmp = qemu_realloc(s->buffer, s->buffer_capacity);
+        if (tmp == NULL) {
+            fprintf(stderr, "qemu file buffer expansion failed\n");
+            exit(1);
+        }
+
+        s->buffer = tmp;
+    }
+
+    memcpy(s->buffer + s->buffer_size, buf, size);
+    s->buffer_size += size;
+}
+
+static void buffered_flush(QEMUFileBuffered *s)
+{
+    size_t offset = 0;
+
+    if (s->has_error) {
+        dprintf("flush when error, bailing\n");
+        return;
+    }
+
+    dprintf("flushing %ld byte(s) of data\n", s->buffer_size);
+
+    while (offset < s->buffer_size) {
+        ssize_t ret;
+
+        ret = s->put_buffer(s->opaque, s->buffer + offset,
+                            s->buffer_size - offset);
+        if (ret == -EAGAIN) {
+            dprintf("backend not ready, freezing\n");
+            s->freeze_output = 1;
+            break;
+        }
+
+        if (ret <= 0) {
+            dprintf("error flushing data, %ld\n", ret);
+            s->has_error = 1;
+            break;
+        } else {
+            dprintf("flushed %ld byte(s)\n", ret);
+            offset += ret;
+        }
+    }
+
+    dprintf("flushed %ld of %ld byte(s)\n", offset, s->buffer_size);
+    memmove(s->buffer, s->buffer + offset, s->buffer_size - offset);
+    s->buffer_size -= offset;
+}
+
+static int buffered_put_buffer(void *opaque, const uint8_t *buf, int64_t pos, int size)
+{
+    QEMUFileBuffered *s = opaque;
+    int offset = 0;
+    ssize_t ret;
+
+    dprintf("putting %ld bytes at %Ld\n", size, pos);
+
+    if (s->has_error) {
+        dprintf("flush when error, bailing\n");
+        return -EINVAL;
+    }
+
+    dprintf("unfreezing output\n");
+    s->freeze_output = 0;
+
+    buffered_flush(s);
+
+    while (!s->freeze_output && offset < size) {
+        if (s->bytes_xfer > s->xfer_limit) {
+            dprintf("transfer limit exceeded when putting\n");
+            break;
+        }
+
+        ret = s->put_buffer(s->opaque, buf + offset, size - offset);
+        if (ret == -EAGAIN) {
+            dprintf("backend not ready, freezing\n");
+            s->freeze_output = 1;
+            break;
+        }
+
+        if (ret <= 0) {
+            dprintf("error putting\n");
+            s->has_error = 1;
+            offset = -EINVAL;
+            break;
+        }
+
+        dprintf("put %ld byte(s)\n", ret);
+        offset += ret;
+        s->bytes_xfer += ret;
+    }
+
+    if (offset >= 0) {
+        dprintf("buffering %ld bytes\n", size - offset);
+        buffered_append(s, buf + offset, size - offset);
+        offset = size;
+    }
+
+    return offset;
+}
+
+static int buffered_close(void *opaque)
+{
+    QEMUFileBuffered *s = opaque;
+    int ret;
+
+    dprintf("closing\n");
+
+    while (!s->has_error && s->buffer_size) {
+        buffered_flush(s);
+        if (s->freeze_output)
+            s->wait_for_unfreeze(s);
+    }
+
+    ret = s->close(s->opaque);
+
+    qemu_del_timer(s->timer);
+    qemu_free_timer(s->timer);
+    qemu_free(s->buffer);
+    qemu_free(s);
+
+    return ret;
+}
+
+static int buffered_rate_limit(void *opaque)
+{
+    QEMUFileBuffered *s = opaque;
+
+    if (s->has_error)
+        return 0;
+
+    if (s->freeze_output)
+        return 1;
+
+    if (s->bytes_xfer > s->xfer_limit)
+        return 1;
+
+    return 0;
+}
+
+static void buffered_rate_tick(void *opaque)
+{
+    QEMUFileBuffered *s = opaque;
+
+    if (s->has_error)
+        return;
+
+    qemu_mod_timer(s->timer, qemu_get_clock(rt_clock) + 100);
+
+    if (s->freeze_output)
+        return;
+
+    s->bytes_xfer = 0;
+
+    buffered_flush(s);
+
+    /* Add some checks around this */
+    s->put_ready(s->opaque);
+}
+
+QEMUFile *qemu_fopen_ops_buffered(void *opaque,
+                                  size_t bytes_per_sec,
+                                  BufferedPutFunc *put_buffer,
+                                  BufferedPutReadyFunc *put_ready,
+                                  BufferedWaitForUnfreezeFunc *wait_for_unfreeze,
+                                  BufferedCloseFunc *close)
+{
+    QEMUFileBuffered *s;
+
+    s = qemu_mallocz(sizeof(*s));
+    if (s == NULL)
+        return NULL;
+
+    s->opaque = opaque;
+    s->xfer_limit = bytes_per_sec / 10;
+    s->put_buffer = put_buffer;
+    s->put_ready = put_ready;
+    s->wait_for_unfreeze = wait_for_unfreeze;
+    s->close = close;
+
+    s->file = qemu_fopen_ops(s, buffered_put_buffer, NULL,
+                             buffered_close, buffered_rate_limit);
+
+    s->timer = qemu_new_timer(rt_clock, buffered_rate_tick, s);
+
+    qemu_mod_timer(s->timer, qemu_get_clock(rt_clock) + 100);
+
+    return s->file;
+}
+