[Xen-devel] [PATCH 06 of 13 v5] blktap3/libblktapctl: Introduce block device control information retrieval functionality

[Thanos Makatos <thanos.makatos@xxxxxxxxxx>]

This patch introduces function tap_ctl_info. It is used by the tapback daemon
to retrieve the size of the block device, as well as the sector size,  in order
to communicate it to blkfront so that it can create the virtual block device.

Signed-off-by: Thanos Makatos <thanos.makatos@xxxxxxxxxx>

---
Changed since v2:
  * Simplified error checking after calling tap_ctl_connect_send_and_receive.

Changed since v4:
  * Remove the minor number and replace it with type:/path/to/file.
  * Remove tap-ctl-info.h and move the definitions into tap-ctl.h.

diff --git a/tools/blktap3/control/tap-ctl-info.c 
b/tools/blktap3/control/tap-ctl-info.c
new file mode 100644
--- /dev/null
+++ b/tools/blktap3/control/tap-ctl-info.c
@@ -0,0 +1,64 @@
+/*
+ * Copyright (C) 2012      Citrix Ltd.
+ *
+ * This program is free software; you can redistribute it and/or
+ * modify it under the terms of the GNU General Public License
+ * as published by the Free Software Foundation; either version 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA  02110-1301,
+ * USA.
+ */
+
+#include <stdio.h>
+#include <string.h>
+#include <assert.h>
+
+#include "tap-ctl.h"
+
+int tap_ctl_info(pid_t pid, const char *path, unsigned long long *sectors,
+        unsigned int *sector_size, unsigned int *info)
+{
+    tapdisk_message_t message;
+    int err;
+
+    assert(sectors);
+    assert(sector_size);
+    assert(info);
+
+    if (!path)
+        return EINVAL;
+    if (strnlen(path, TAPDISK_MESSAGE_STRING_LENGTH)
+            >= TAPDISK_MESSAGE_STRING_LENGTH)
+        return ENAMETOOLONG;
+
+    memset(&message, 0, sizeof(message));
+    message.type = TAPDISK_MESSAGE_DISK_INFO;
+    strcpy(message.u.string.text, path);
+
+    err = tap_ctl_connect_send_and_receive(pid, &message, NULL);
+    if (err) {
+        EPRINTF("failed to get info from tapdisk %d: %s\n", pid,
+                strerror(err));
+        return err;
+    }
+
+    if (TAPDISK_MESSAGE_DISK_INFO_RSP == message.type) {
+        *sectors = message.u.image.sectors;
+        *sector_size = message.u.image.sector_size;
+        *info = message.u.image.info;
+        return 0;
+    } else if (TAPDISK_MESSAGE_ERROR == message.type) {
+       return message.u.response.error;
+    } else {
+        EPRINTF("unexpected reply %d\n", message.type);
+        return -EINVAL;
+    }
+}

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