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libdevmapper: _do_event waits for working dmeventd

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Refactor _start_daemon and add synchronization delay waiting
untill new forked dmeventd actually open fifos and is ready
to process messages.

This closes some race window in testing.
This commit is contained in:
Zdenek Kabelac 2024-04-19 20:45:00 +02:00
parent 85b711caae
commit 79bb9e3172
1 changed files with 47 additions and 19 deletions
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66
daemons/dmeventd/libdevmapper-event.c
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@ -400,25 +400,16 @@ int daemon_talk(struct dm_event_fifos *fifos,
return (int32_t) msg->cmd;
}
/*
* start_daemon
* Check for usable client fifo file
*
* This function forks off a process (dmeventd) that will handle
* the events. I am currently test opening one of the fifos to
* ensure that the daemon is running and listening... I thought
* this would be less expensive than fork/exec'ing every time.
* Perhaps there is an even quicker/better way (no, checking the
* lock file is _not_ a better way).
*
* Returns: 1 on success, 0 otherwise
* Returns: 2 cliant path does not exists, dmeventd should be restarted
* 1 on success, 0 otherwise
*/
static int _start_daemon(char *dmeventd_path, struct dm_event_fifos *fifos)
static int _check_for_usable_fifos(char *dmeventd_path, struct dm_event_fifos *fifos)
{
int pid, ret = 0;
int status;
struct stat statbuf;
char default_dmeventd_path[] = DMEVENTD_PATH;
char *args[] = { dmeventd_path ? : default_dmeventd_path, NULL };
/*
* FIXME Explicitly verify the code's requirement that client_path is secure:
@ -429,7 +420,7 @@ static int _start_daemon(char *dmeventd_path, struct dm_event_fifos *fifos)
if ((lstat(fifos->client_path, &statbuf) < 0)) {
if (errno == ENOENT)
/* Jump ahead if fifo does not already exist. */
goto start_server;
return 2;
else {
log_sys_error("stat", fifos->client_path);
return 0;
@ -461,6 +452,7 @@ static int _start_daemon(char *dmeventd_path, struct dm_event_fifos *fifos)
/* server is running and listening */
if (close(fifos->client))
log_sys_debug("close", fifos->client_path);
fifos->client = -1;
return 1;
}
if (errno != ENXIO && errno != ENOENT) {
@ -469,9 +461,36 @@ static int _start_daemon(char *dmeventd_path, struct dm_event_fifos *fifos)
return 0;
}
start_server:
/* server is not running */
return 2;
}
/*
* start_daemon
*
* This function forks off a process (dmeventd) that will handle
* the events. I am currently test opening one of the fifos to
* ensure that the daemon is running and listening... I thought
* this would be less expensive than fork/exec'ing every time.
* Perhaps there is an even quicker/better way (no, checking the
* lock file is _not_ a better way).
*
* Returns: 1 on success, 0 otherwise
*/
static int _start_daemon(char *dmeventd_path, struct dm_event_fifos *fifos)
{
struct stat statbuf;
char default_dmeventd_path[] = DMEVENTD_PATH;
char *args[] = { dmeventd_path ? : default_dmeventd_path, NULL };
int pid, ret = 0;
int status;
switch (_check_for_usable_fifos(dmeventd_path, fifos)) {
case 0: return_0;
case 1: return 1; /* Already running dmeventd */
}
/* server is not running */
if ((args[0][0] == '/') && stat(args[0], &statbuf)) {
log_sys_error("stat", args[0]);
return 0;
@ -492,8 +511,17 @@ start_server:
strerror(errno));
else if (WEXITSTATUS(status))
log_error("Unable to start dmeventd.");
else
ret = 1;
else {
/* Loop here till forked dmeventd is serving fifos */
for (ret = 100; ret > 0; --ret)
switch (_check_for_usable_fifos(dmeventd_path, fifos)) {
case 0: return_0;
case 1: return 1;
case 2: usleep(1000); continue;
}
/* ret == 0 */
log_error("Dmeventd is not serving fifos.");
}
}
return ret;