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Subject[PATCH] tracing: Add saved_tgids file to show cached pid to tgid mappings
Export the cached pid / tgid mappings to userspace. This allows user
apps to translate the pids from a trace to their respective thread
group.

Example saved_tgids file with pid / tgid values separated by ' ':

# cat saved_tgids
1048 1048
1047 1047
7 7
1049 1047
1054 1047
1053 1047

[ Impact: let userspace apps reading binary buffer know tgid's ]

Signed-off-by: Michael Sartain <mikesart@fastmail.com>
---
kernel/trace/trace.c | 60 +++++++++++++++++++++++++++++++++++++++++++++++++++-
1 file changed, 59 insertions(+), 1 deletion(-)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 68c214b..ca84c97 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4692,6 +4692,7 @@ static const struct file_operations tracing_readme_fops = {
static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
{
unsigned int *ptr = v;
+ long tgid_check = (long) m->private;

if (*pos || m->count)
ptr++;
@@ -4702,6 +4703,8 @@ static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
ptr++) {
if (*ptr == -1 || *ptr == NO_CMDLINE_MAP)
continue;
+ if (tgid_check && !trace_find_tgid(*ptr))
+ continue;

return ptr;
}
@@ -4713,6 +4716,10 @@ static void *saved_cmdlines_start(struct seq_file *m, loff_t *pos)
{
void *v;
loff_t l = 0;
+ long tgid_check = (long) m->private;
+
+ if (tgid_check && !tgid_map)
+ return NULL;

preempt_disable();
arch_spin_lock(&trace_cmdline_lock);
@@ -4743,6 +4750,14 @@ static int saved_cmdlines_show(struct seq_file *m, void *v)
return 0;
}

+static int saved_tgids_show(struct seq_file *m, void *v)
+{
+ unsigned int *pid = v;
+
+ seq_printf(m, "%d %d\n", *pid, trace_find_tgid(*pid));
+ return 0;
+}
+
static const struct seq_operations tracing_saved_cmdlines_seq_ops = {
.start = saved_cmdlines_start,
.next = saved_cmdlines_next,
@@ -4750,12 +4765,45 @@ static const struct seq_operations tracing_saved_cmdlines_seq_ops = {
.show = saved_cmdlines_show,
};

+static const struct seq_operations tracing_saved_tgids_seq_ops = {
+ .start = saved_cmdlines_start,
+ .next = saved_cmdlines_next,
+ .stop = saved_cmdlines_stop,
+ .show = saved_tgids_show,
+};
+
static int tracing_saved_cmdlines_open(struct inode *inode, struct file *filp)
{
+ int ret;
+
+ if (tracing_disabled)
+ return -ENODEV;
+
+ ret = seq_open(filp, &tracing_saved_cmdlines_seq_ops);
+ if (!ret) {
+ struct seq_file *m = filp->private_data;
+
+ m->private = (void *) 0; /* Do not check for valid tgids */
+ }
+
+ return ret;
+}
+
+static int tracing_saved_tgids_open(struct inode *inode, struct file *filp)
+{
+ int ret;
+
if (tracing_disabled)
return -ENODEV;

- return seq_open(filp, &tracing_saved_cmdlines_seq_ops);
+ ret = seq_open(filp, &tracing_saved_tgids_seq_ops);
+ if (!ret) {
+ struct seq_file *m = filp->private_data;
+
+ m->private = (void *) 1; /* Check for valid tgids */
+ }
+
+ return ret;
}

static const struct file_operations tracing_saved_cmdlines_fops = {
@@ -4765,6 +4813,13 @@ static const struct file_operations tracing_saved_cmdlines_fops = {
.release = seq_release,
};

+static const struct file_operations tracing_saved_tgids_fops = {
+ .open = tracing_saved_tgids_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
static ssize_t
tracing_saved_cmdlines_size_read(struct file *filp, char __user *ubuf,
size_t cnt, loff_t *ppos)
@@ -7933,6 +7988,9 @@ static __init int tracer_init_tracefs(void)
trace_create_file("saved_cmdlines_size", 0644, d_tracer,
NULL, &tracing_saved_cmdlines_size_fops);

+ trace_create_file("saved_tgids", 0444, d_tracer,
+ NULL, &tracing_saved_tgids_fops);
+
trace_eval_init();

trace_create_eval_file(d_tracer);
--
2.11.0
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