[sheepdog] [PATCH] sheep: cache sha1 digest for read-only objects

[MORITA Kazutaka]

The contents of read-only objects are immutable.  We can cache their
sha1 digests as extended attributes for the next sha1 calculation.
With this patch, I can complete 'collie vdi check' of a 4 GB snapshot
volume in 0.2 seconds.

Signed-off-by: MORITA Kazutaka <morita.kazutaka at lab.ntt.co.jp>
---

This patch is against my "use hash for vdi check and object recovery" series.

 sheep/farm/farm.c   |  5 -----
 sheep/plain_store.c | 49 +++++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/sheep/farm/farm.c b/sheep/farm/farm.c
index c31c501..38586f5 100644
--- a/sheep/farm/farm.c
+++ b/sheep/farm/farm.c
@@ -98,11 +98,6 @@ static int farm_init(void)
 	if (create_directory(obj_path) < 0)
 		goto err;
 
-	if (!is_xattr_enabled(obj_path)) {
-		sd_eprintf("xattrs are not enabled on %s", obj_path);
-		goto err;
-	}
-
 	if (snap_init() < 0)
 		goto err;
 
diff --git a/sheep/plain_store.c b/sheep/plain_store.c
index 3b71467..5f0a131 100644
--- a/sheep/plain_store.c
+++ b/sheep/plain_store.c
@@ -12,6 +12,7 @@
 #include <fcntl.h>
 #include <sys/stat.h>
 #include <sys/types.h>
+#include <sys/xattr.h>
 #include <unistd.h>
 #include <libgen.h>
 
@@ -220,6 +221,12 @@ int default_init(void)
 	int ret;
 
 	sd_dprintf("use plain store driver");
+
+	if (!is_xattr_enabled(obj_path)) {
+		sd_eprintf("xattrs are not enabled on %s", obj_path);
+		return SD_RES_EIO;
+	}
+
 	ret = for_each_obj_path(make_stale_dir);
 	if (ret != SD_RES_SUCCESS)
 		return ret;
@@ -476,6 +483,41 @@ int default_remove_object(uint64_t oid)
 	return SD_RES_SUCCESS;
 }
 
+#define SHA1NAME "user.obj.sha1"
+
+static int get_sha1_cache(uint64_t oid, uint32_t epoch, uint8_t *sha1)
+{
+	char path[PATH_MAX];
+
+	if (!oid_is_readonly(oid))
+		return -1;
+
+	if (default_exist(oid))
+		get_obj_path(oid, path);
+	else
+		get_stale_obj_path(oid, epoch, path);
+
+	if (getxattr(path, SHA1NAME, sha1, SHA1_LEN) != SHA1_LEN)
+		return -1;
+
+	return 0;
+}
+
+static int set_sha1_cache(uint64_t oid, uint32_t epoch, const uint8_t *sha1)
+{
+	char path[PATH_MAX];
+
+	if (!oid_is_readonly(oid))
+		return -1;
+
+	if (default_exist(oid))
+		get_obj_path(oid, path);
+	else
+		get_stale_obj_path(oid, epoch, path);
+
+	return setxattr(path, SHA1NAME, sha1, SHA1_LEN, 0);
+}
+
 int default_get_hash(uint64_t oid, uint32_t epoch, uint8_t *sha1)
 {
 	int ret;
@@ -485,6 +527,11 @@ int default_get_hash(uint64_t oid, uint32_t epoch, uint8_t *sha1)
 	uint64_t offset = 0;
 	uint32_t length;
 
+	if (get_sha1_cache(oid, epoch, sha1) == 0) {
+		sd_dprintf("use cached sha1 digest %s", sha1_to_hex(sha1));
+		return SD_RES_SUCCESS;
+	}
+
 	length = get_objsize(oid);
 	buf = malloc(length);
 	if (buf == NULL)
@@ -512,6 +559,8 @@ int default_get_hash(uint64_t oid, uint32_t epoch, uint8_t *sha1)
 	sd_dprintf("the message digest of %"PRIx64" at epoch %d is %s", oid,
 		   epoch, sha1_to_hex(sha1));
 
+	set_sha1_cache(oid, epoch, sha1);
+
 	return ret;
 }
 
-- 
1.8.1.3.566.gaa39828