[PATCH 5.18 702/879] rtla: Remove procps-ng dependency

Greg Kroah-Hartman
2022-06-08T02:03:27Z

From: Daniel Bristot de Oliveira <bristot@kernel.org>

[ Upstream commit dada03db9bb1984826e61cfcf1418ac73848324d ]

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.

Link: https://lkml.kernel.org/r/e8276e122ee9eb2c5a0ba8e673fb6488b924b825.1652423574.git.bristot@kernel.org

Cc: John Kacur <jkacur@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Tao Zhou <tao.zhou@linux.dev>
Fixes: b1696371d865 ("rtla: Helper functions for rtla")
Reported-by: Daniel Wagner <dwagner@suse.de>
Reviewed-by: Daniel Wagner <dwagner@suse.de>
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
tools/tracing/rtla/Makefile | 2 +-
tools/tracing/rtla/README.txt | 1 -
tools/tracing/rtla/src/utils.c | 106 ++++++++++++++++++++++++++-------
tools/tracing/rtla/src/utils.h | 3 +-
4 files changed, 88 insertions(+), 24 deletions(-)

diff --git a/tools/tracing/rtla/Makefile b/tools/tracing/rtla/Makefile
index 5a3226e436ef..523f0a8c38c2 100644
--- a/tools/tracing/rtla/Makefile
+++ b/tools/tracing/rtla/Makefile
@@ -32,7 +32,7 @@ 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 0fbad2640b8c..4af3fd40f171 100644
--- a/tools/tracing/rtla/README.txt
+++ b/tools/tracing/rtla/README.txt
@@ -11,7 +11,6 @@ RTLA depends on the following libraries and tools:

- 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 3bd6f64780cf..5352167a1e75 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>
@@ -262,43 +262,107 @@ int __set_sched_attr(int pid, struct sched_attr *attr)

return 0;
}
+
+/*
+ * procfs_is_workload_pid - check if a procfs entry contains a comm_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 *comm_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 comm_prefix*.
+ * Otherwise returns false.
+ */
+static int procfs_is_workload_pid(const char *comm_prefix, struct dirent *proc_entry)
+{
+ char buffer[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(buffer, MAX_PATH, "/proc/%s/comm", proc_entry->d_name);
+ comm_fd = open(buffer, O_RDONLY);
+ if (comm_fd < 0)
+ return 0;
+
+ memset(buffer, 0, MAX_PATH);
+ retval = read(comm_fd, buffer, MAX_PATH);
+
+ close(comm_fd);
+
+ if (retval <= 0)
+ return 0;
+
+ retval = strncmp(comm_prefix, buffer, strlen(comm_prefix));
+ if (retval)
+ return 0;
+
+ /* comm already have \n */
+ debug_msg("Found workload pid:%s comm:%s", proc_entry->d_name, buffer);
+
+ return 1;
+}
+
/*
- * set_comm_sched_attr - set sched params to threads starting with char *comm
+ * set_comm_sched_attr - set sched params to threads starting with char *comm_prefix
*
- * This function uses procps to list the currently running threads and then
- * set the sched_attr *attr to the threads that start with char *comm. It is
+ * This function uses procfs to list the currently running threads and then set the
+ * sched_attr *attr to the threads that start with char *comm_prefix. It is
* mainly used to set the priority to the kernel threads created by the
* tracers.
*/
-int set_comm_sched_attr(const char *comm, struct sched_attr *attr)
+int set_comm_sched_attr(const char *comm_prefix, 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;
+ if (strlen(comm_prefix) >= MAX_PATH) {
+ err_msg("Command prefix is too long: %d < strlen(%s)\n",
+ MAX_PATH, comm_prefix);
+ return 1;
}

- memset(&task, 0, sizeof(task));
+ procfs = opendir("/proc");
+ if (!procfs) {
+ err_msg("Could not open procfs\n");
+ return 1;
+ }

- while (readproc(ptp, &task)) {
- retval = strncmp(comm, task.cmd, strlen(comm));
- if (retval)
+ while ((proc_entry = readdir(procfs))) {
+
+ retval = procfs_is_workload_pid(comm_prefix, proc_entry);
+ if (!retval)
continue;
- retval = __set_sched_attr(task.tid, attr);
- if (retval)
+
+ /* procfs_is_workload_pid confirmed it is a pid */
+ retval = __set_sched_attr(atoi(proc_entry->d_name), attr);
+ if (retval) {
+ err_msg("Error setting sched attributes for pid:%s\n", proc_entry->d_name);
goto out_err;
- }
+ }

- closeproc(ptp);
+ debug_msg("Set sched attributes for pid:%s\n", proc_entry->d_name);
+ }
return 0;

out_err:
- closeproc(ptp);
+ closedir(procfs);
return 1;
}

diff --git a/tools/tracing/rtla/src/utils.h b/tools/tracing/rtla/src/utils.h
index fa08e374870a..5571afd3b549 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); \
@@ -53,5 +54,5 @@ struct sched_attr {
};

int parse_prio(char *arg, struct sched_attr *sched_param);
-int set_comm_sched_attr(const char *comm, struct sched_attr *attr);
+int set_comm_sched_attr(const char *comm_prefix, struct sched_attr *attr);
int set_cpu_dma_latency(int32_t latency);
--
2.35.1