[sheepdog] [PATCH v4 2/2] sheep: implement atomic create and write mechanism for config

[Hitoshi Mitake]

From: Hitoshi Mitake <mitake.hito...@gmail.com>

Because we cannot utilize the journaling mechanism for config, this
patch implements atomic creation and writing for it.

Signed-off-by: Hitoshi Mitake <mitake.hito...@lab.ntt.co.jp>
---
v4: remove the unnecessary global variable

v3:
 - rephrase the message of check_tmp_config()
 - remove a redundant constant

v2: use access(2) for checking remained temporal file

 sheep/config.c |   30 ++++++++++++++++++++++++++++--
 1 files changed, 28 insertions(+), 2 deletions(-)

diff --git a/sheep/config.c b/sheep/config.c
index 49916e7..6bc092b 100644
--- a/sheep/config.c
+++ b/sheep/config.c
@@ -36,10 +36,13 @@ char *config_path;
 static int write_config(void)
 {
        int fd, ret;
+       char tmp_config_path[PATH_MAX];
 
-       fd = open(config_path, O_RDWR | O_CREAT | O_DSYNC, def_fmode);
+       snprintf(tmp_config_path, PATH_MAX, "%s.tmp", config_path);
+
+       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 +54,36 @@ 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)
+{
+       char tmp_config_path[PATH_MAX];
+
+       snprintf(tmp_config_path, PATH_MAX, "%s.tmp", config_path);
+
+       if (!access(tmp_config_path, F_OK))
+               return;
+
+       sd_iprintf("remove temporal config file");
+       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) {
-- 
1.7.2.5

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