[sheepdog] [PATCH 2/2] sheep: implement atomic create and write mechanism for config

[Hitoshi Mitake]

Signed-off-by: Hitoshi Mitake <mitake.hito...@lab.ntt.co.jp>
---
 sheep/config.c |   33 ++++++++++++++++++++++++++++++---
 1 files changed, 30 insertions(+), 3 deletions(-)

diff --git a/sheep/config.c b/sheep/config.c
index 49916e7..a2ffd8c 100644
--- a/sheep/config.c
+++ b/sheep/config.c
@@ -29,17 +29,18 @@ static struct sheepdog_config {
        uint64_t space;
 } config;
 
-char *config_path;
+char *config_path, *tmp_config_path;
 
 #define CONFIG_PATH "/config"
+#define TMP_CONFIG_PATH "/config.tmp"
 
 static int write_config(void)
 {
        int fd, ret;
 
-       fd = open(config_path, O_RDWR | O_CREAT | O_DSYNC, def_fmode);
+       fd = open(tmp_config_path, O_WRONLY | O_CREAT | O_SYNC, def_fmode);
        if (fd < 0) {
-               sd_eprintf("failed to open config file, %m");
+               sd_eprintf("failed to temporal file for config, %m");
                return SD_RES_EIO;
        }
 
@@ -51,13 +52,35 @@ static int write_config(void)
                ret = SD_RES_SUCCESS;
        close(fd);
 
+       ret = rename(tmp_config_path, config_path);
+       if (ret < 0) {
+               sd_eprintf("failed to rename, %m");
+               ret = SD_RES_EIO;
+       }
+
+       unlink(tmp_config_path);
+
        return ret;
 }
 
+static void check_tmp_config(void)
+{
+       int fd;
+
+       fd = open(tmp_config_path, O_RDONLY);
+       if (fd < 0 && errno == ENOENT)
+               return;
+
+       sd_iprintf("temporal file for config exists");
+       unlink(tmp_config_path);
+}
+
 int init_config_file(void)
 {
        int fd, ret;
 
+       check_tmp_config();
+
        fd = open(config_path, O_RDONLY);
        if (fd < 0) {
                if (errno != ENOENT) {
@@ -119,6 +142,10 @@ void init_config_path(const char *base_path)
 
        config_path = xzalloc(len);
        snprintf(config_path, len, "%s" CONFIG_PATH, base_path);
+
+       len = strlen(base_path) + strlen(TMP_CONFIG_PATH) + 1;
+       tmp_config_path = xzalloc(len);
+       snprintf(tmp_config_path, len, "%s" TMP_CONFIG_PATH, base_path);
 }
 
 int set_cluster_ctime(uint64_t ct)
-- 
1.7.5.1

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