[1/4] qemu-char: Add new char backend CirMemCharDriver

diff --git a/qemu-char.c b/qemu-char.c
index b082bae..45d2a86 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -99,6 +99,7 @@ 
 #include "ui/qemu-spice.h"
 
 #define READ_BUF_LEN 4096
+#define CBUFF_SIZE 65536
 
 /***********************************************************/
 /* character device */
@@ -2588,6 +2589,130 @@  size_t qemu_chr_mem_osize(const CharDriverState *chr)
     return d->outbuf_size;
 }
 
+/*********************************************************/
+/*CircularMemoryr chardev*/
+
+typedef struct {
+    size_t size;
+    size_t producer;
+    size_t consumer;
+    uint8_t *cbuf;
+} CirMemCharDriver;
+
+static bool cirmem_chr_is_empty(const CharDriverState *chr)
+{
+    const CirMemCharDriver *d = chr->opaque;
+
+    return d->producer == d->consumer;
+}
+
+static bool cirmem_chr_is_full(const CharDriverState *chr)
+{
+    const CirMemCharDriver *d = chr->opaque;
+
+    return (d->producer - d->consumer) >= d->size;
+}
+
+static bool cirmem_chr_unlimit(const CharDriverState *chr)
+{
+    const CirMemCharDriver *d = chr->opaque;
+
+    return d->producer >= d->consumer;
+}
+
+static int cirmem_chr_write(CharDriverState *chr, const uint8_t *buf, int len)
+{
+    CirMemCharDriver *d = chr->opaque;
+    int i;
+
+    if (!buf || (len < 0)) {
+        return -1;
+    }
+
+    for (i = 0; i < len; i++ ) {
+        if (cirmem_chr_unlimit(chr)) {
+            d->cbuf[d->producer % d->size] = buf[i];
+            d->producer++;
+        } else {
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static int cirmem_chr_read(CharDriverState *chr, uint8_t *buf, int len)
+{
+    CirMemCharDriver *d = chr->opaque;
+    int i;
+
+    if (cirmem_chr_is_empty(chr) || len < 0) {
+        return -1;
+    }
+
+    if (len > d->size) {
+        len = d->size;
+    }
+
+    for (i = 0; i < len; i++) {
+        if (cirmem_chr_unlimit(chr)) {
+            buf[i] = d->cbuf[d->consumer % d->size];
+            d->consumer++;
+
+            if (cirmem_chr_is_empty(chr)) {
+                break;
+            }
+        } else {
+            return -1;
+        }
+    }
+
+    return 0;
+}
+
+static void cirmem_chr_close(struct CharDriverState *chr)
+{
+    CirMemCharDriver *d = chr->opaque;
+
+    g_free(d->cbuf);
+    g_free(d);
+    chr->opaque = NULL;
+}
+
+static CharDriverState *qemu_chr_open_cirmemchr(QemuOpts *opts)
+{
+    CharDriverState *chr;
+    CirMemCharDriver *d;
+
+    chr = g_malloc0(sizeof(CharDriverState));
+    d = g_malloc(sizeof(*d));
+
+    d->size = qemu_opt_get_number(opts, "maxcapacity", 0);
+    if (d->size == 0) {
+        d->size = CBUFF_SIZE;
+    }
+
+    /* The size must be power of 2 */
+    if (d->size & (d->size - 1)) {
+        goto fail;
+    }
+
+    d->producer = 0;
+    d->consumer = 0;
+    d->cbuf = g_malloc0(d->size);
+
+    chr->opaque = d;
+    chr->chr_write = cirmem_chr_write;
+    chr->chr_close = cirmem_chr_close;
+
+    return chr;
+
+fail:
+    g_free(d);
+    g_free(chr);
+    return NULL;
+}
+
 QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
 {
     char host[65], port[33], width[8], height[8];
@@ -2652,6 +2777,16 @@  QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
         qemu_opt_set(opts, "path", p);
         return opts;
     }
+    if (strstart(filename, "memchr", &p)) {
+        qemu_opt_set(opts, "backend", "memchr");
+        qemu_opt_set(opts, "maxcapacity", p);
+        return opts;
+    }
+    if (strstart(filename, "memchr", &p)) {
+        qemu_opt_set(opts, "backend", "memchr");
+        qemu_opt_set(opts, "maxcapacity", p);
+        return opts;
+    }
     if (strstart(filename, "tcp:", &p) ||
         strstart(filename, "telnet:", &p)) {
         if (sscanf(p, "%64[^:]:%32[^,]%n", host, port, &pos) < 2) {
@@ -2725,6 +2860,7 @@  static const struct {
     { .name = "udp",       .open = qemu_chr_open_udp },
     { .name = "msmouse",   .open = qemu_chr_open_msmouse },
     { .name = "vc",        .open = text_console_init },
+    { .name = "memchr",    .open = qemu_chr_open_cirmemchr },
 #ifdef _WIN32
     { .name = "file",      .open = qemu_chr_open_win_file_out },
     { .name = "pipe",      .open = qemu_chr_open_win_pipe },
diff --git a/qemu-config.c b/qemu-config.c
index cd1ec21..5553bb6 100644
--- a/qemu-config.c
+++ b/qemu-config.c
@@ -213,6 +213,9 @@  static QemuOptsList qemu_chardev_opts = {
         },{
             .name = "debug",
             .type = QEMU_OPT_NUMBER,
+        },{
+            .name = "maxcapacity",
+            .type = QEMU_OPT_NUMBER,
         },
         { /* end of list */ }
     },
diff --git a/qemu-options.hx b/qemu-options.hx
index 46f0539..9ccf930 100644
--- a/qemu-options.hx
+++ b/qemu-options.hx
@@ -1680,6 +1680,7 @@  DEF("chardev", HAS_ARG, QEMU_OPTION_chardev,
     "-chardev msmouse,id=id[,mux=on|off]\n"
     "-chardev vc,id=id[[,width=width][,height=height]][[,cols=cols][,rows=rows]]\n"
     "         [,mux=on|off]\n"
+    "-chardev memchr,id=id,maxcapacity=maxcapacity\n"
     "-chardev file,id=id,path=path[,mux=on|off]\n"
     "-chardev pipe,id=id,path=path[,mux=on|off]\n"
 #ifdef _WIN32
@@ -1718,6 +1719,7 @@  Backend is one of:
 @option{udp},
 @option{msmouse},
 @option{vc},
+@option{memchr},
 @option{file},
 @option{pipe},
 @option{console},
@@ -1824,6 +1826,14 @@  the console, in pixels.
 @option{cols} and @option{rows} specify that the console be sized to fit a text
 console with the given dimensions.
 
+@item -chardev memchr ,id=@var{id} ,maxcapacity=@var{maxcapacity}
+
+Create a circular buffer with fixed size indicated by optionally @option{maxcapacity}
+which will be default 64K if it is not given.
+
+@option{maxcapacity} specify the max capacity of the size of circular buffer
+want to create. Should be power of 2.
+
 @item -chardev file ,id=@var{id} ,path=@var{path}
 
 Log all traffic received from the guest to a file.