[sheepdog] [PATCH 1/2] dog: add a new option for reducing identical snapshots

[Hitoshi Mitake]

Current "dog vdi snapshot" command creates a new snapshot
unconditionally, even if a working VDI doesn't have its own
objects. In such a case, the created snapshot is redundant because
same VDI is already existing.

This patch adds a new option -R to the dog command for reducing
the identical snapshots.

Signed-off-by: Hitoshi Mitake <mitake.hitoshi at lab.ntt.co.jp>
---
 dog/vdi.c | 48 +++++++++++++++++++++++++++++++++++++++++++++++-
 1 file changed, 47 insertions(+), 1 deletion(-)

diff --git a/dog/vdi.c b/dog/vdi.c
index 8e612af..ee465c2 100644
--- a/dog/vdi.c
+++ b/dog/vdi.c
@@ -40,6 +40,8 @@ static struct sd_option vdi_options[] = {
 	 "                          neither comparing nor repairing"},
 	{'z', "block_size_shift", true, "specify the bit shift num for"
 			       " data object size"},
+	{'R', "reduce-identical-snapshots", false, "do not create snapshot if "
+	 "working VDI doesn't have its own objects"},
 	{ 0, NULL, false, NULL },
 };
 
@@ -61,6 +63,7 @@ static struct vdi_cmd_data {
 	uint64_t oid;
 	bool no_share;
 	bool exist;
+	bool reduce_identical_snapshots;
 } vdi_cmd_data = { ~0, };
 
 struct get_vdi_info {
@@ -605,6 +608,31 @@ fail:
 	return NULL;
 }
 
+static bool has_own_objects(uint32_t vid, int *ret)
+{
+	struct sd_inode *inode;
+	bool result = true;
+
+	inode = xzalloc(sizeof(*inode));
+
+	*ret = dog_read_object(vid_to_vdi_oid(vid), inode,
+			      sizeof(*inode), 0, true);
+	if (*ret != SD_RES_SUCCESS)
+		goto out;
+
+	for (int i = 0; i < SD_INODE_DATA_INDEX; i++) {
+		if (inode->data_vdi_id[i] && inode->data_vdi_id[i] == vid)
+			/* VDI has its own object */
+			goto out;
+	}
+
+	result = false;
+
+out:
+	free(inode);
+	return result;
+}
+
 static int vdi_snapshot(int argc, char **argv)
 {
 	const char *vdiname = argv[optind++];
@@ -703,6 +731,22 @@ static int vdi_snapshot(int argc, char **argv)
 		nr_issued_prevent_inode_update++;
 	}
 
+	if (vdi_cmd_data.reduce_identical_snapshots) {
+		bool result = has_own_objects(vid, &ret);
+
+		if (ret != SD_RES_SUCCESS)
+			goto out;
+
+		if (!result) {
+			if (verbose)
+				sd_info("VDI %s doesn't have its own objects, "
+					"skipping creation of snapshot",
+					vdiname);
+
+			goto out;
+		}
+	}
+
 	ret = dog_write_object(vid_to_vdi_oid(vid), 0,
 			       vdi_cmd_data.snapshot_tag,
 			       SD_MAX_VDI_TAG_LEN,
@@ -3057,7 +3101,7 @@ static struct subcommand vdi_cmd[] = {
 	{"create", "<vdiname> <size>", "PycaphrvzT", "create an image",
 	 NULL, CMD_NEED_NODELIST|CMD_NEED_ARG,
 	 vdi_create, vdi_options},
-	{"snapshot", "<vdiname>", "saphrvT", "create a snapshot",
+	{"snapshot", "<vdiname>", "saphrvTR", "create a snapshot",
 	 NULL, CMD_NEED_ARG,
 	 vdi_snapshot, vdi_options},
 	{"clone", "<src vdi> <dst vdi>", "sPnaphrvT", "clone an image",
@@ -3222,6 +3266,8 @@ static int vdi_parser(int ch, const char *opt)
 		}
 		vdi_cmd_data.block_size_shift = block_size_shift;
 		break;
+	case 'R':
+		vdi_cmd_data.reduce_identical_snapshots = true;
 	}
 
 	return 0;
-- 
1.9.1