[Qemu-devel] [PATCH 3/4] QAPI: Introduce memchar-read QMP command

[Lei Li <lilei@linux.vnet.ibm.com>]

Signed-off-by: Lei Li <lilei@linux.vnet.ibm.com>
---
 hmp-commands.hx  |   19 ++++++++++++++++++
 hmp.c            |   17 ++++++++++++++++
 hmp.h            |    1 +
 qapi-schema.json |   27 ++++++++++++++++++++++++-
 qemu-char.c      |   57 ++++++++++++++++++++++++++++++++++++++++++++++++++++++
 qmp-commands.hx  |   34 ++++++++++++++++++++++++++++++++
 6 files changed, 154 insertions(+), 1 deletions(-)

diff --git a/hmp-commands.hx b/hmp-commands.hx
index 305b0d7..c79c9d3 100644
--- a/hmp-commands.hx
+++ b/hmp-commands.hx
@@ -855,6 +855,25 @@ to char device 'memory'.
 ETEXI
 
     {
+        .name       = "memchar_read",
+        .args_type  = "chardev:s,size:i",
+        .params     = "chardev size",
+        .mhandler.cmd = hmp_memchar_read,
+    },
+
+STEXI
+@item memchar_read @var{chardev}
+@findex memchar_read
+Provide read interface for CirMemCharDriver. Read from char device
+'memory' and return @var{size} of 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
+
+    {
         .name       = "migrate",
         .args_type  = "detach:-d,blk:-b,inc:-i,uri:s",
         .params     = "[-d] [-b] [-i] uri",
diff --git a/hmp.c b/hmp.c
index 1ffb3d6..0465c42 100644
--- a/hmp.c
+++ b/hmp.c
@@ -695,6 +695,23 @@ 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, "chardev");
+    char *data;
+    Error *errp = NULL;
+
+    data = qmp_memchar_read(chardev, size, false, 0, &errp);
+    if (errp) {
+        monitor_printf(mon, "%s\n", error_get_pretty(errp));
+        error_free(errp);
+        return;
+    }
+
+    monitor_printf(mon, "%s\n", data);
+}
+
 static void hmp_cont_cb(void *opaque, int err)
 {
     if (!err) {
diff --git a/hmp.h b/hmp.h
index 6c3ec45..6289037 100644
--- a/hmp.h
+++ b/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);
diff --git a/qapi-schema.json b/qapi-schema.json
index f0acaac..0696902 100644
--- a/qapi-schema.json
+++ b/qapi-schema.json
@@ -346,7 +346,7 @@
 #
 # @chardev: the name of the memory char device.
 #
-# @size: the size to write in bytes. Should be power of 2.
+# @size: the size to write in bytes.
 #
 # @data: the source data write to memchar.
 #
@@ -366,6 +366,31 @@
            '*format': 'DataFormat'} }
 
 ##
+# @memchar-read:
+#
+# Provide read interface for memchardev. Read from the char
+# device 'memory' and return the data.
+#
+# @chardev: 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: The data read from memchar as string
+#          If @chardev is not a valid memchr device, DeviceNotFound
+#
+# Notes: For now assume 'drop' behaver, which would result in reads
+#        returning empty strings.
+#
+# Since: 1.3
+##
+{ 'command': 'memchar-read',
+  'data': {'chardev': 'str', 'size': 'int', '*format': 'DataFormat'},
+  'returns': 'str' }
+
+##
 # @CommandInfo:
 #
 # Information about a QMP command
diff --git a/qemu-char.c b/qemu-char.c
index 92b4cec..a16276a 100644
--- a/qemu-char.c
+++ b/qemu-char.c
@@ -2771,6 +2771,63 @@ void qmp_memchar_write(const char *chardev, int64_t size,
     }
 }
 
+char *qmp_memchar_read(const char *chardev, int64_t size,
+                       bool has_format, enum DataFormat format,
+                       Error **errp)
+{
+    CharDriverState *chr;
+    guchar *read_data;
+    char *data = NULL;
+    int ret;
+    size_t count;
+
+    chr = qemu_chr_find(chardev);
+    if (!chr) {
+        error_set(errp, QERR_DEVICE_NOT_FOUND, chardev);
+        return NULL;
+    }
+
+    if (qemu_is_chr(chr, "memory")) {
+        error_setg(errp,"%s is not memory char device\n", chardev);
+        return NULL;
+    }
+
+    if (size <= 0) {
+        error_setg(errp, "Failed to read from device %s", chardev);
+        return NULL;
+    }
+
+    /* XXX: Return the empty strings when the buffer is empty. */
+    if (cirmem_chr_is_empty(chr)) {
+        error_setg(errp, "Memory device %s is empty", chardev);
+        return NULL;
+    }
+
+    count = qemu_chr_cirmem_count(chr);
+    size = size > count ? count : size;
+    read_data = g_malloc0(size + 1);
+
+    ret = cirmem_chr_read(chr, read_data, size);
+    if (ret < 0) {
+        error_setg(errp, "Failed to read from device %s", chardev);
+        goto fail;
+    }
+
+    if (has_format && (format == DATA_FORMAT_BASE64)) {
+       if (read_data) {
+           data = g_base64_encode(read_data, (size_t)size);
+       }
+    } else {
+        data = (char *)read_data;
+    }
+
+    return data;
+
+fail:
+    g_free(read_data);
+    return NULL;
+}
+
 QemuOpts *qemu_chr_parse_compat(const char *label, const char *filename)
 {
     char host[65], port[33], width[8], height[8];
diff --git a/qmp-commands.hx b/qmp-commands.hx
index ae3ab5a..2e9b33a 100644
--- a/qmp-commands.hx
+++ b/qmp-commands.hx
@@ -500,6 +500,40 @@ Example:
 EQMP
 
     {
+        .name       = "memchar-read",
+        .args_type  = "chardev:s,size:i,format:s?",
+        .help       = "return the size of data from memchar chardev",
+        .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.
+
+Arguments:
+
+- "chardev": 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": { "chardev": foo,
+                               "size": 1000,
+                               "format": "utf8" } }
+<- { "return": "data string..." }
+
+EQMP
+
+    {
         .name       = "xen-save-devices-state",
         .args_type  = "filename:F",
     .mhandler.cmd_new = qmp_marshal_input_xen_save_devices_state,
-- 
1.7.7.6