[Qemu-devel] [PATCH 1/3] qemu-char: Introduce Buffered driver

[Luiz Capitulino <lcapitulino@redhat.com>]

This driver handles in-memory chardev operations. That's, all writes
to this driver are stored in an internal buffer and it doesn't talk
to the external world in any way.

Right now it's very simple: it supports only writes. But it can be
easily extended to support more operations.

This is going to be used by the monitor's "HMP passthrough via QMP"
feature, which needs to run monitor handlers without a backing
device.

Signed-off-by: Luiz Capitulino <lcapitulino@redhat.com>
---
 qemu-char.c |   63 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 qemu-char.h |    6 +++++
 2 files changed, 69 insertions(+), 0 deletions(-)

diff --git a/qemu-char.c b/qemu-char.c
index 6d2dce7..a4bd09c 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2279,6 +2279,69 @@ static CharDriverState *qemu_chr_open_socket(QemuOpts *opts)
     return NULL;
 }
 
+/***********************************************************/
+/* Buffered chardev */
+typedef struct {
+    size_t outbuf_size;
+    size_t outbuf_capacity;
+    uint8_t *outbuf;
+} BufferedDriver;
+
+static int buffered_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
+{
+    BufferedDriver *d = chr->opaque;
+
+    if (d->outbuf_capacity < (d->outbuf_size + len)) {
+        /* grown outbuf */
+        d->outbuf_capacity += len;
+        d->outbuf_capacity *= 2;
+        d->outbuf = qemu_realloc(d->outbuf, d->outbuf_capacity);
+    }
+
+    memcpy(d->outbuf + d->outbuf_size, buf, len);
+    d->outbuf_size += len;
+
+    return len;
+}
+
+#define DEFAULT_BUF_SIZE 4096
+
+void qemu_chr_init_buffered(CharDriverState *chr)
+{
+    BufferedDriver *d;
+
+    d = qemu_malloc(sizeof(*d));
+    d->outbuf_size = 0;
+    d->outbuf_capacity = DEFAULT_BUF_SIZE;
+    d->outbuf = qemu_mallocz(d->outbuf_capacity);
+
+    memset(chr, 0, sizeof(*chr));
+    chr->opaque = d;
+    chr->chr_write = buffered_chr_write;
+}
+
+/* assumes the stored data is a string */
+QString *qemu_chr_buffered_to_qs(CharDriverState *chr)
+{
+    BufferedDriver *d = chr->opaque;
+
+    if (d->outbuf_size == 0) {
+        return NULL;
+    }
+
+    return qstring_from_substr((char *) d->outbuf, 0, d->outbuf_size - 1);
+}
+
+void qemu_chr_close_buffered(CharDriverState *chr)
+{
+    BufferedDriver *d = chr->opaque;
+
+    qemu_free(d->outbuf);
+    qemu_free(chr->opaque);
+    chr->opaque = NULL;
+    chr->chr_write = NULL;
+}
+
 QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
 {
     char host[65], port[33], width[8], height[8];
diff --git a/qemu-char.h b/qemu-char.h
index 18ad12b..4467641 100644
--- a/qemu-char.h
+++ b/qemu-char.h
@@ -6,6 +6,7 @@
 #include "qemu-option.h"
 #include "qemu-config.h"
 #include "qobject.h"
+#include "qstring.h"
 
 /* character device */
 
@@ -100,6 +101,11 @@ CharDriverState *qemu_chr_open_eventfd(int eventfd);
 
 extern int term_escape_char;
 
+/* buffered chardev */
+void qemu_chr_init_buffered(CharDriverState *chr);
+void qemu_chr_close_buffered(CharDriverState *chr);
+QString *qemu_chr_buffered_to_qs(CharDriverState *chr);
+
 /* async I/O support */
 
 int qemu_set_fd_handler2(int fd,
-- 
1.7.3.2.145.g7ebee