[PATCH 1/2] rtla: Remove procps-ng dependency

[PATCH 1/2] rtla: Remove procps-ng dependency

[Daniel Bristot de Oliveira]

Daniel Wagner reported to me that readproc.h got deprecated. Also,
while the procps-ng library was available on Fedora, it was not available
on RHEL, which is a piece of evidence that it was not that used.

rtla uses procps-ng only to find the PID of the tracers' workload.

I used the procps-ng library to avoid reinventing the wheel. But in this
case, reinventing the wheel took me less time than the time we already
took trying to work around problems.

Implement a function that reads /proc/ entries, checking if:
	- the entry is a directory
	- the directory name is composed only of digits (PID)
	- the directory contains the comm file
	- the comm file contains a comm that matches the tracers'
	  workload prefix.
	- then return true; otherwise, return false.

And use it instead of procps-ng.

Cc: John Kacur <jkacur@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Fixes: b1696371d865 ("rtla: Helper functions for rtla")
Reported-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
 tools/tracing/rtla/Makefile    |  2 +-
 tools/tracing/rtla/README.txt  |  1 -
 tools/tracing/rtla/src/utils.c | 83 +++++++++++++++++++++++++++-------
 tools/tracing/rtla/src/utils.h |  1 +
 4 files changed, 68 insertions(+), 19 deletions(-)

diff --git a/tools/tracing/rtla/Makefile b/tools/tracing/rtla/Makefile
index 11fb417abb42..90b8e20d1118 100644
--- a/tools/tracing/rtla/Makefile
+++ b/tools/tracing/rtla/Makefile
@@ -31,7 +31,7 @@ TRACEFS_HEADERS	:= $$($(PKG_CONFIG) --cflags libtracefs)
 
 CFLAGS	:=	-O -g -DVERSION=\"$(VERSION)\" $(FOPTS) $(MOPTS) $(WOPTS) $(TRACEFS_HEADERS)
 LDFLAGS	:=	-ggdb
-LIBS	:=	$$($(PKG_CONFIG) --libs libtracefs) -lprocps
+LIBS	:=	$$($(PKG_CONFIG) --libs libtracefs)
 
 SRC	:=	$(wildcard src/*.c)
 HDR	:=	$(wildcard src/*.h)
diff --git a/tools/tracing/rtla/README.txt b/tools/tracing/rtla/README.txt
index 6c88446f7e74..7bc0b931ddfd 100644
--- a/tools/tracing/rtla/README.txt
+++ b/tools/tracing/rtla/README.txt
@@ -13,7 +13,6 @@ following libraries:
 
  - libtracefs
  - libtraceevent
- - procps
 
 It also depends on python3-docutils to compile man pages.
 
diff --git a/tools/tracing/rtla/src/utils.c b/tools/tracing/rtla/src/utils.c
index da2b590edaed..baf9003d5d41 100644
--- a/tools/tracing/rtla/src/utils.c
+++ b/tools/tracing/rtla/src/utils.c
@@ -3,7 +3,7 @@
  * Copyright (C) 2021 Red Hat Inc, Daniel Bristot de Oliveira <bristot@kernel.org>
  */
 
-#include <proc/readproc.h>
+#include <dirent.h>
 #include <stdarg.h>
 #include <stdlib.h>
 #include <string.h>
@@ -262,6 +262,62 @@ int __set_sched_attr(int pid, struct sched_attr *attr)
 
 	return 0;
 }
+
+/*
+ * procfs_is_workload_pid - check if a procfs entry contains a workload_prefix* comm
+ *
+ * Check if the procfs entry is a directory of a process, and then check if the
+ * process has a comm with the prefix set in char *workload_prefix. As the
+ * current users of this function only check for kernel threads, there is no
+ * need to check for the threads for the process.
+ *
+ * Return: True if the proc_entry contains a comm file with workload_prefix*.
+ * Otherwise returns false.
+ */
+static int procfs_is_workload_pid(const char *workload_prefix, struct dirent *proc_entry)
+{
+	char comm_path[MAX_PATH], comm[MAX_PATH];
+	int comm_fd, retval;
+	char *t_name;
+
+	if (proc_entry->d_type != DT_DIR)
+		return 0;
+
+	if (*proc_entry->d_name == '.')
+		return 0;
+
+	/* check if the string is a pid */
+	for (t_name = proc_entry->d_name; t_name; t_name++) {
+		if (!isdigit(*t_name))
+			break;
+	}
+
+	if (*t_name != '\0')
+		return 0;
+
+	snprintf(comm_path, MAX_PATH, "/proc/%s/comm", proc_entry->d_name);
+	comm_fd = open(comm_path, O_RDONLY);
+	if (comm_fd < 0)
+		return 0;
+
+	memset(comm, 0, MAX_PATH);
+	retval = read(comm_fd, comm, MAX_PATH);
+
+	close(comm_fd);
+
+	if (retval <= 0)
+		return 0;
+
+	retval = !strncmp(workload_prefix, comm, strlen(workload_prefix));
+	if (!retval)
+		return 0;
+
+	/* comm already have \n */
+	debug_msg("Found workload pid:%s comm:%s", proc_entry->d_name, comm);
+
+	return 1;
+}
+
 /*
  * set_comm_sched_attr - set sched params to threads starting with char *comm
  *
@@ -272,33 +328,26 @@ int __set_sched_attr(int pid, struct sched_attr *attr)
  */
 int set_comm_sched_attr(const char *comm, struct sched_attr *attr)
 {
-	int flags = PROC_FILLCOM | PROC_FILLSTAT;
-	PROCTAB *ptp;
-	proc_t task;
+	struct dirent *proc_entry;
+	DIR *procfs;
 	int retval;
 
-	ptp = openproc(flags);
-	if (!ptp) {
-		err_msg("error openproc()\n");
-		return -ENOENT;
-	}
+	procfs = opendir("/proc");
 
-	memset(&task, 0, sizeof(task));
+	while ((proc_entry = readdir(procfs))) {
 
-	while (readproc(ptp, &task)) {
-		retval = strncmp(comm, task.cmd, strlen(comm));
-		if (retval)
+		retval = procfs_is_workload_pid(comm, proc_entry);
+		if (!retval)
 			continue;
-		retval = __set_sched_attr(task.tid, attr);
+
+		/* procfs_is_workload_pid confirmed it is a pid */
+		retval = __set_sched_attr(atoi(proc_entry->d_name), attr);
 		if (retval)
 			goto out_err;
 	}
-
-	closeproc(ptp);
 	return 0;
 
 out_err:
-	closeproc(ptp);
 	return 1;
 }
 
diff --git a/tools/tracing/rtla/src/utils.h b/tools/tracing/rtla/src/utils.h
index fa08e374870a..4959a3e2c0d5 100644
--- a/tools/tracing/rtla/src/utils.h
+++ b/tools/tracing/rtla/src/utils.h
@@ -6,6 +6,7 @@
  * '18446744073709551615\0'
  */
 #define BUFF_U64_STR_SIZE	24
+#define MAX_PATH		1024
 
 #define container_of(ptr, type, member)({			\
 	const typeof(((type *)0)->member) *__mptr = (ptr);	\
-- 
2.35.1

[PATCH 2/2] rtla: Fix __set_sched_attr error message

[Daniel Bristot de Oliveira]

rtla's function __set_sched_attr() was borrowed from stalld, but I
forgot to update the error message to something meaningful for rtla.

 Update the error message from:
        boost_with_deadline failed to boost pid PID: STRERROR
 to a proper one:
        Failed to set sched attributes to the pid PID: STRERROR

Cc: Steven Rostedt <rostedt@goodmis.org>
Fixes: b1696371d865 ("rtla: Helper functions for rtla")
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
---
 tools/tracing/rtla/src/utils.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/tracing/rtla/src/utils.c b/tools/tracing/rtla/src/utils.c
index baf9003d5d41..60dd48315315 100644
--- a/tools/tracing/rtla/src/utils.c
+++ b/tools/tracing/rtla/src/utils.c
@@ -255,7 +255,7 @@ int __set_sched_attr(int pid, struct sched_attr *attr)
 
 	retval = sched_setattr(pid, attr, flags);
 	if (retval < 0) {
-		err_msg("boost_with_deadline failed to boost pid %d: %s\n",
+		err_msg("Failed to set sched attributes to the pid %d: %s\n",
 			pid, strerror(errno));
 		return 1;
 	}
-- 
2.35.1

Re: [PATCH 1/2] rtla: Remove procps-ng dependency

[Steven Rostedt]

On Fri, 22 Apr 2022 12:01:31 +0200
Daniel Bristot de Oliveira <bristot@kernel.org> wrote:


> +
> +/*
> + * procfs_is_workload_pid - check if a procfs entry contains a workload_prefix* comm
> + *
> + * Check if the procfs entry is a directory of a process, and then check if the
> + * process has a comm with the prefix set in char *workload_prefix. As the
> + * current users of this function only check for kernel threads, there is no
> + * need to check for the threads for the process.
> + *
> + * Return: True if the proc_entry contains a comm file with workload_prefix*.
> + * Otherwise returns false.
> + */
> +static int procfs_is_workload_pid(const char *workload_prefix, struct dirent *proc_entry)
> +{
> +	char comm_path[MAX_PATH], comm[MAX_PATH];

This is probably fine (but there is one issue), but I would have done this
a little different.

	int len = strlen(workload_prefix);
	char comm[len + 1];

> +	int comm_fd, retval;
> +	char *t_name;
> +
> +	if (proc_entry->d_type != DT_DIR)
> +		return 0;
> +
> +	if (*proc_entry->d_name == '.')
> +		return 0;
> +
> +	/* check if the string is a pid */
> +	for (t_name = proc_entry->d_name; t_name; t_name++) {
> +		if (!isdigit(*t_name))
> +			break;
> +	}
> +
> +	if (*t_name != '\0')
> +		return 0;
> +
> +	snprintf(comm_path, MAX_PATH, "/proc/%s/comm", proc_entry->d_name);
> +	comm_fd = open(comm_path, O_RDONLY);
> +	if (comm_fd < 0)
> +		return 0;
> +
> +	memset(comm, 0, MAX_PATH);

No need for the memset.

> +	retval = read(comm_fd, comm, MAX_PATH);

	retval = read(comm_fd, comm, len + 1);

> +
> +	close(comm_fd);
> +
> +	if (retval <= 0)
> +		return 0;

	if (comm[len] != '\n')
		return 0;

> +
> +	retval = !strncmp(workload_prefix, comm, strlen(workload_prefix));

What happens if strlen(workload_prefix) is greater than MAX_PATH? ;-)

	retval = !strncmp(workload_prefix, comm, len);

But that's me. If you want to keep this as is, let me know.

-- Steve



> +	if (!retval)
> +		return 0;
> +
> +	/* comm already have \n */
> +	debug_msg("Found workload pid:%s comm:%s", proc_entry->d_name, comm);
> +
> +	return 1;
> +}
> +

Re: [PATCH 1/2] rtla: Remove procps-ng dependency

[Daniel Bristot de Oliveira]

On 4/26/22 03:45, Steven Rostedt wrote:
> On Fri, 22 Apr 2022 12:01:31 +0200
> Daniel Bristot de Oliveira <bristot@kernel.org> wrote:
> 
> 
>> +
>> +/*
>> + * procfs_is_workload_pid - check if a procfs entry contains a workload_prefix* comm
>> + *
>> + * Check if the procfs entry is a directory of a process, and then check if the
>> + * process has a comm with the prefix set in char *workload_prefix. As the
>> + * current users of this function only check for kernel threads, there is no
>> + * need to check for the threads for the process.
>> + *
>> + * Return: True if the proc_entry contains a comm file with workload_prefix*.
>> + * Otherwise returns false.
>> + */
>> +static int procfs_is_workload_pid(const char *workload_prefix, struct dirent *proc_entry)
>> +{
>> +	char comm_path[MAX_PATH], comm[MAX_PATH];
> 
> This is probably fine (but there is one issue), but I would have done this
> a little different.
> 
> 	int len = strlen(workload_prefix);
> 	char comm[len + 1];
> 
>> +	int comm_fd, retval;
>> +	char *t_name;
>> +
>> +	if (proc_entry->d_type != DT_DIR)
>> +		return 0;
>> +
>> +	if (*proc_entry->d_name == '.')
>> +		return 0;
>> +
>> +	/* check if the string is a pid */
>> +	for (t_name = proc_entry->d_name; t_name; t_name++) {
>> +		if (!isdigit(*t_name))
>> +			break;
>> +	}
>> +
>> +	if (*t_name != '\0')
>> +		return 0;
>> +
>> +	snprintf(comm_path, MAX_PATH, "/proc/%s/comm", proc_entry->d_name);
>> +	comm_fd = open(comm_path, O_RDONLY);
>> +	if (comm_fd < 0)
>> +		return 0;
>> +
>> +	memset(comm, 0, MAX_PATH);
> 
> No need for the memset.
> 
>> +	retval = read(comm_fd, comm, MAX_PATH);
> 
> 	retval = read(comm_fd, comm, len + 1);
> 
>> +
>> +	close(comm_fd);
>> +
>> +	if (retval <= 0)
>> +		return 0;
> 
> 	if (comm[len] != '\n')
> 		return 0;
> 
>> +
>> +	retval = !strncmp(workload_prefix, comm, strlen(workload_prefix));
> 
> What happens if strlen(workload_prefix) is greater than MAX_PATH? ;-)

That is a concern I had, but we have only two use cases on rtla so far, and they
are both bounded: 'timerlat/' 'osnoise/'...

I will add a check though.

> 
> 	retval = !strncmp(workload_prefix, comm, len);
> 
> But that's me. If you want to keep this as is, let me know.

I made these changes... but I am loosing the debug_msg() with the comm/pid that
matched. I am adding these messages (and I plan to add more) so I can use on
testing scripts...

At the same time, I can share a char buffer[MAX_PATH] for both the comm and
comm_path...

I think I will go this way (using a single buffer), adding a warning... and...

> -- Steve
> 
> 
> 
>> +	if (!retval)
>> +		return 0;

also removing ! in the the revtal = !strcmp(...); if (!retval).

Thoughts?

-- Daniel

>> +
>> +	/* comm already have \n */
>> +	debug_msg("Found workload pid:%s comm:%s", proc_entry->d_name, comm);
>> +
>> +	return 1;
>> +}
>> +