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Subject[PATCH 12/22] perf daemon: Allow only one daemon over base directory
Date
Add 'lock' file under daemon base and flock it, so only one
perf daemon can run on top of it.

Example:

# cat ~/.perfconfig
[daemon]
base=/opt/perfdata

[session-cycles]
run = -m 10M -e cycles --overwrite --switch-output -a

[session-sched]
run = -m 20M -e sched:* --overwrite --switch-output -a

Starting the daemon:

# perf daemon start

And try once more:

# perf daemon start
failed: another perf daemon (pid 775594) owns /opt/perfdata

will end up with an error, because there's already one running
on top of /opt/perfdata.

Signed-off-by: Jiri Olsa <jolsa@kernel.org>
---
tools/perf/builtin-daemon.c | 49 +++++++++++++++++++++++++++++++++++++
1 file changed, 49 insertions(+)

diff --git a/tools/perf/builtin-daemon.c b/tools/perf/builtin-daemon.c
index 45748bb471ec..1982eedd3f3f 100644
--- a/tools/perf/builtin-daemon.c
+++ b/tools/perf/builtin-daemon.c
@@ -8,6 +8,7 @@
#include <string.h>
#include <sys/types.h>
#include <sys/wait.h>
+#include <sys/file.h>
#include <signal.h>
#include <stdlib.h>
#include <time.h>
@@ -562,12 +563,18 @@ static int cmd_session_list(struct daemon *daemon, union cmd *cmd, FILE *out)
/* output */
csv_sep, daemon->base, SESSION_OUTPUT);

+ fprintf(out, "%c%s/%s",
+ /* lock */
+ csv_sep, daemon->base, "lock");
+
fprintf(out, "\n");
} else {
fprintf(out, "[%d:daemon] base: %s\n", getpid(), daemon->base);
if (cmd->list.verbose) {
fprintf(out, " output: %s/%s\n",
daemon->base, SESSION_OUTPUT);
+ fprintf(out, " lock: %s/lock\n",
+ daemon->base);
}
}

@@ -761,6 +768,42 @@ static int handle_config_changes(struct daemon *daemon, int conf_fd,
return 0;
}

+static int check_lock(struct daemon *daemon)
+{
+ char path[PATH_MAX];
+ char buf[20];
+ int fd, pid;
+ ssize_t len;
+
+ scnprintf(path, sizeof(path), "%s/lock", daemon->base);
+
+ fd = open(path, O_RDWR|O_CREAT|O_CLOEXEC, 0640);
+ if (fd < 0)
+ return -1;
+
+ if (lockf(fd, F_TLOCK, 0) < 0) {
+ filename__read_int(path, &pid);
+ fprintf(stderr, "failed: another perf daemon (pid %d) owns %s\n",
+ pid, daemon->base);
+ return -1;
+ }
+
+ scnprintf(buf, sizeof(buf), "%d", getpid());
+ len = strlen(buf);
+
+ if (write(fd, buf, len) != len) {
+ perror("write failed");
+ return -1;
+ }
+
+ if (ftruncate(fd, len)) {
+ perror("ftruncate failed");
+ return -1;
+ }
+
+ return 0;
+}
+
static int go_background(struct daemon *daemon)
{
int pid, fd;
@@ -775,6 +818,9 @@ static int go_background(struct daemon *daemon)
if (setsid() < 0)
return -1;

+ if (check_lock(daemon))
+ return -1;
+
umask(0);

if (chdir(daemon->base)) {
@@ -861,6 +907,9 @@ static int __cmd_start(struct daemon *daemon, struct option parent_options[],
if (setup_server_config(daemon))
return -1;

+ if (foreground && check_lock(daemon))
+ return -1;
+
if (!foreground && go_background(daemon))
return -1;

--
2.26.2
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