QAPI: Introduce memchar-read QMP command

Signed-off-by: NLei Li <lilei@linux.vnet.ibm.com>
Signed-off-by: NLuiz Capitulino <lcapitulino@redhat.com>

hmp-commands.hx

@@ -855,6 +855,27 @@ STEXI
 Provide writing interface for CirMemCharDriver. Write @var{data}
 to char device 'memory'.
 
+ETEXI
+
+    {
+        .name       = "memchar_read",
+        .args_type  = "device:s,size:i",
+        .params     = "device size",
+        .help       = "Provide read interface for CirMemCharDriver. Read from"
+                      "it and return the data with size.",
+        .mhandler.cmd = hmp_memchar_read,
+    },
+
+STEXI
+@item memchar_read @var{device}
+@findex memchar_read
+Provide read interface for CirMemCharDriver. Read from char device
+'memory' and return the data.
+
+@var{size} is the size of data want to read from. Refer to unencoded
+size of the raw data, would adjust to the init size of the memchar
+if the requested size is larger than it.
+
 ETEXI
 
     {

hmp.c

@@ -675,6 +675,27 @@ void hmp_memchar_write(Monitor *mon, const QDict *qdict)
     hmp_handle_error(mon, &errp);
 }
 
+void hmp_memchar_read(Monitor *mon, const QDict *qdict)
+{
+    uint32_t size = qdict_get_int(qdict, "size");
+    const char *chardev = qdict_get_str(qdict, "device");
+    MemCharRead *meminfo;
+    Error *errp = NULL;
+
+    meminfo = qmp_memchar_read(chardev, size, false, 0, &errp);
+    if (errp) {
+        monitor_printf(mon, "%s\n", error_get_pretty(errp));
+        error_free(errp);
+        return;
+    }
+
+    if (meminfo->count > 0) {
+        monitor_printf(mon, "%s\n", meminfo->data);
+    }
+
+    qapi_free_MemCharRead(meminfo);
+}
+
 static void hmp_cont_cb(void *opaque, int err)
 {
     if (!err) {

hmp.h

@@ -44,6 +44,7 @@ void hmp_cpu(Monitor *mon, const QDict *qdict);
 void hmp_memsave(Monitor *mon, const QDict *qdict);
 void hmp_pmemsave(Monitor *mon, const QDict *qdict);
 void hmp_memchar_write(Monitor *mon, const QDict *qdict);
+void hmp_memchar_read(Monitor *mon, const QDict *qdict);
 void hmp_cont(Monitor *mon, const QDict *qdict);
 void hmp_system_wakeup(Monitor *mon, const QDict *qdict);
 void hmp_inject_nmi(Monitor *mon, const QDict *qdict);

qapi-schema.json

@@ -362,6 +362,42 @@
   'data': {'device': 'str', 'size': 'int', 'data': 'str',
            '*format': 'DataFormat'} }
 
+##
+# @MemCharRead
+#
+# Result of QMP command memchar-read.
+#
+# @data: The data read from memchar as string.
+#
+# @count: The numbers of bytes read from.
+#
+# Since: 1.4
+##
+{ 'type': 'MemCharRead',
+  'data': { 'data': 'str', 'count': 'int' } }
+
+##
+# @memchar-read:
+#
+# Provide read interface for memchardev. Read from the char
+# device 'memory' and return the data.
+#
+# @device: the name of the memory char device.
+#
+# @size: the size to read in bytes.
+#
+# @format: #optional the format of the data want to read from
+#          memchardev, by default is 'utf8'.
+#
+# Returns: @MemCharRead
+#          If @device is not a valid memchr device, DeviceNotFound
+#
+# Since: 1.4
+##
+{ 'command': 'memchar-read',
+  'data': {'device': 'str', 'size': 'int', '*format': 'DataFormat'},
+  'returns': 'MemCharRead' }
+
 ##
 # @CommandInfo:
 #

qemu-char.c

@@ -2790,6 +2790,53 @@ void qmp_memchar_write(const char *device, int64_t size,
     }
 }
 
+MemCharRead *qmp_memchar_read(const char *device, int64_t size,
+                              bool has_format, enum DataFormat format,
+                              Error **errp)
+{
+    CharDriverState *chr;
+    guchar *read_data;
+    MemCharRead *meminfo;
+    size_t count;
+
+    chr = qemu_chr_find(device);
+    if (!chr) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, device);
+        return NULL;
+    }
+
+    if (qemu_is_chr(chr, "memory")) {
+        error_setg(errp,"%s is not memory char device", device);
+        return NULL;
+    }
+
+    if (size <= 0) {
+        error_setg(errp, "size must be greater than zero");
+        return NULL;
+    }
+
+    meminfo = g_malloc0(sizeof(MemCharRead));
+
+    count = qemu_chr_cirmem_count(chr);
+    if (count == 0) {
+        meminfo->data = g_strdup("");
+        return meminfo;
+    }
+
+    size = size > count ? count : size;
+    read_data = g_malloc0(size + 1);
+
+    meminfo->count = cirmem_chr_read(chr, read_data, size);
+
+    if (has_format && (format == DATA_FORMAT_BASE64)) {
+        meminfo->data = g_base64_encode(read_data, (size_t)meminfo->count);
+    } else {
+        meminfo->data = (char *)read_data;
+    }
+
+    return meminfo;
+}
+
 QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
 {
     char host[65], port[33], width[8], height[8];

qmp-commands.hx

@@ -496,6 +496,39 @@ Example:
                                "format": "utf8" } }
 <- { "return": {} }
 
+EQMP
+
+    {
+        .name       = "memchar-read",
+        .args_type  = "device:s,size:i,format:s?",
+        .mhandler.cmd_new = qmp_marshal_input_memchar_read,
+    },
+
+SQMP
+memchar-read
+-------------
+
+Provide read interface for CirMemCharDriver. Read from the char
+device memory and return the data with size.
+
+Arguments:
+
+- "device": the name of the char device, must be unique (json-string)
+- "size": the memory size wanted to read in bytes (refer to unencoded
+          size of the raw data), would adjust to the init size of the
+          memchar if the requested size is larger than it. (json-int)
+- "format": the data format write to memchardev, default is
+            utf8. (json-string, optional)
+          - Possible values: "utf8", "base64"
+
+Example:
+
+-> { "execute": "memchar-read",
+                "arguments": { "device": foo,
+                               "size": 1000,
+                               "format": "utf8" } }
+<- { "return": { "data": "data string...", "count": 1000 } }
+
 EQMP
 
     {