[PATCH v2] trace-cmd: Move trace_msg cache file to memfd

[PATCH v2] trace-cmd: Move trace_msg cache file to memfd

[Joel Fernandes]

This is cleaner and also fixes issues in Android where /tmp does not
exist.

With this, host-guest tracing works on Android VM running on ChromeOS
Linux.

Signed-off-by: Joel Fernandes <joel@joelfernandes.org>
---
 lib/trace-cmd/include/private/trace-cmd-private.h | 2 --
 lib/trace-cmd/trace-msg.c                         | 4 +---
 2 files changed, 1 insertion(+), 5 deletions(-)

diff --git a/lib/trace-cmd/include/private/trace-cmd-private.h b/lib/trace-cmd/include/private/trace-cmd-private.h
index 6934376..3aee139 100644
--- a/lib/trace-cmd/include/private/trace-cmd-private.h
+++ b/lib/trace-cmd/include/private/trace-cmd-private.h
@@ -377,7 +377,6 @@ enum tracecmd_msg_flags {
 };
 
 /* for both client and server */
-#define MSG_CACHE_FILE "/tmp/trace_msg_cacheXXXXXX"
 struct tracecmd_msg_handle {
 	int			fd;
 	short			cpu_count;
@@ -386,7 +385,6 @@ struct tracecmd_msg_handle {
 	bool			done;
 	bool			cache;
 	int			cfd;
-	char			cfile[sizeof(MSG_CACHE_FILE)];
 };
 
 struct tracecmd_tsync_protos {
diff --git a/lib/trace-cmd/trace-msg.c b/lib/trace-cmd/trace-msg.c
index 03b853e..1472f20 100644
--- a/lib/trace-cmd/trace-msg.c
+++ b/lib/trace-cmd/trace-msg.c
@@ -593,11 +593,9 @@ tracecmd_msg_handle_alloc(int fd, unsigned long flags)
 int tracecmd_msg_handle_cache(struct tracecmd_msg_handle *msg_handle)
 {
 	if (msg_handle->cfd < 0) {
-		strcpy(msg_handle->cfile, MSG_CACHE_FILE);
-		msg_handle->cfd = mkstemp(msg_handle->cfile);
+		msg_handle->cfd = memfd_create("trace_msg_cache", 0);
 		if (msg_handle->cfd < 0)
 			return -1;
-		unlink(msg_handle->cfile);
 	}
 	msg_handle->cache = true;
 	return 0;
-- 
2.35.1.1094.g7c7d902a7c-goog

Re: [PATCH v2] trace-cmd: Move trace_msg cache file to memfd

[Steven Rostedt]

On Sun,  3 Apr 2022 23:18:25 +0000
Joel Fernandes <joel@joelfernandes.org> wrote:

> +++ b/lib/trace-cmd/trace-msg.c
> @@ -593,11 +593,9 @@ tracecmd_msg_handle_alloc(int fd, unsigned long flags)
>  int tracecmd_msg_handle_cache(struct tracecmd_msg_handle *msg_handle)
>  {
>  	if (msg_handle->cfd < 0) {
> -		strcpy(msg_handle->cfile, MSG_CACHE_FILE);
> -		msg_handle->cfd = mkstemp(msg_handle->cfile);
> +		msg_handle->cfd = memfd_create("trace_msg_cache", 0);
>  		if (msg_handle->cfd < 0)
>  			return -1;
> -		unlink(msg_handle->cfile);
>  	}

This causes:

trace-profile.c:23:3: warning: #warning "lib audit not found, using raw syscalls " "(install audit-libs-devel(for fedora) or libaudit-dev(for debian/ubuntu) and try again)" [-Wcpp]
   23 | # warning "lib audit not found, using raw syscalls "    \
      |   ^~~~~~~


Care to send a v3 update?

Man page shows:

SYNOPSIS
       #define _GNU_SOURCE         /* See feature_test_macros(7) */
       #include <sys/mman.h>

       int memfd_create(const char *name, unsigned int flags);

Note, all of trace-cmd is compiled with _GNU_SOURCE set.

-- Steve