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Make JSON create atomic #2661

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Make JSON create atomic #2661

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34 changes: 32 additions & 2 deletions keepalived/vrrp/vrrp_json.c
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Original file line number Diff line number Diff line change
Expand Up @@ -25,8 +25,10 @@
#include "config.h"
#include "vrrp_json.h"

#include <fcntl.h>
#include <errno.h>
#include <stdio.h>
#include <unistd.h>

#include "vrrp.h"
#include "vrrp_track.h"
Expand Down Expand Up @@ -360,19 +362,47 @@ vrrp_json_dump(FILE *fp)
void
vrrp_print_json(void)
{
int fd;
FILE *fp;
const char *filename;
char file_tmp_name[PATH_MAX];
int sav_errno;

if (list_empty(&vrrp_data->vrrp))
return;

filename = make_tmp_filename("keepalived.json");
fp = fopen_safe(filename, "we");

/* write to a temporary file and rename it afterwards to avoid dealing with filesystem locks */
strcpy_safe(file_tmp_name, filename);
if (strlen(filename) + 6 < sizeof(file_tmp_name))
strcat(file_tmp_name, "XXXXXX");
else
strcpy(file_tmp_name + sizeof(file_tmp_name) - 6 - 1, "XXXXXX");

fd = mkostemp(file_tmp_name, O_CLOEXEC);
if (fd == -1) {
sav_errno = errno;
log_message(LOG_INFO, "Unable to create temporary json file '%s' - errno %d (%m)", file_tmp_name, errno);
errno = sav_errno;
FREE_CONST(filename);
return;
} else
close(fd);

fp = fopen_safe(file_tmp_name, "ae");
if (fp) {
vrrp_json_dump(fp);
fclose(fp);
if (rename(file_tmp_name, filename)) {
sav_errno = errno;
log_message(LOG_INFO, "Failed to rename %s to %s - errno %d (%m)", file_tmp_name, filename, errno);
errno = sav_errno;
FREE_CONST(filename);
return;
}
} else
log_message(LOG_INFO, "Can't open %s/keepalived.json (%d: %m)", tmp_dir, errno);
log_message(LOG_INFO, "Can't create %s (%d: %m)", filename, errno);

FREE_CONST(filename);
}