qemu-img info: show nocow info

Add nocow info in 'qemu-img info' output to show whether the file
currently has NOCOW flag set or not.
Signed-off-by: Chunyan Liu <cyliu@suse.com>
Reviewed-by: Eric Blake <eblake@redhat.com>
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>

block/qapi.c

@@ -28,6 +28,13 @@
 #include "qapi-visit.h"
 #include "qapi/qmp-output-visitor.h"
 #include "qapi/qmp/types.h"
+#ifdef __linux__
+#include <linux/fs.h>
+#include <sys/ioctl.h>
+#ifndef FS_NOCOW_FL
+#define FS_NOCOW_FL                     0x00800000 /* Do not cow file */
+#endif
+#endif
 
 BlockDeviceInfo *bdrv_block_device_info(BlockDriverState *bs)
 {
@@ -172,6 +179,9 @@ void bdrv_query_image_info(BlockDriverState *bs,
     int ret;
     Error *err = NULL;
     ImageInfo *info;
+#ifdef __linux__
+    int fd, attr;
+#endif
 
     size = bdrv_getlength(bs);
     if (size < 0) {
@@ -201,6 +211,18 @@ void bdrv_query_image_info(BlockDriverState *bs,
     info->format_specific     = bdrv_get_specific_info(bs);
     info->has_format_specific = info->format_specific != NULL;
 
+#ifdef __linux__
+    /* get NOCOW info */
+    fd = qemu_open(bs->filename, O_RDONLY | O_NONBLOCK);
+    if (fd >= 0) {
+        if (ioctl(fd, FS_IOC_GETFLAGS, &attr) == 0 && (attr & FS_NOCOW_FL)) {
+            info->has_nocow = true;
+            info->nocow = true;
+        }
+        qemu_close(fd);
+    }
+#endif
+
     backing_filename = bs->backing_file;
     if (backing_filename[0] != '\0') {
         info->backing_filename = g_strdup(backing_filename);
@@ -631,4 +653,8 @@ void bdrv_image_info_dump(fprintf_function func_fprintf, void *f,
         func_fprintf(f, "Format specific information:\n");
         bdrv_image_info_specific_dump(func_fprintf, f, info->format_specific);
     }
+
+    if (info->has_nocow && info->nocow) {
+        func_fprintf(f, "NOCOW flag: set\n");
+    }
 }

qapi/block-core.json

@@ -115,6 +115,8 @@
 # @format-specific: #optional structure supplying additional format-specific
 # information (since 1.7)
 #
+# @nocow: #optional info of whether NOCOW flag is set or not. (since 2.2)
+#
 # Since: 1.3
 #
 ##
@@ -126,7 +128,8 @@
            '*backing-filename': 'str', '*full-backing-filename': 'str',
            '*backing-filename-format': 'str', '*snapshots': ['SnapshotInfo'],
            '*backing-image': 'ImageInfo',
-           '*format-specific': 'ImageInfoSpecific' } }
+           '*format-specific': 'ImageInfoSpecific',
+           '*nocow': 'bool' } }
 
 ##
 # @ImageCheck: