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Subject[PATCH v2] tracing: Add saved_tgids file to show cached pid to tgid mappings
Export the cached pid / tgid mappings added by Joel Fernandes' patch [1]
in debugfs tracing saved_tgids file. 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

Let userspace apps reading binary buffer know tgid's.

[1] https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg1434654.html

Reviewed-by: Joel Fernandes <joelaf@google.com>
Signed-off-by: Michael Sartain <mikesart@fastmail.com>
---
[v2] Don't reuse cmdlines code for saved_tgids file.

kernel/trace/trace.c | 73 ++++++++++++++++++++++++++++++++++++++++++++++++++++
1 file changed, 73 insertions(+)

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c72c36c..e962fb3 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -4701,6 +4701,76 @@ static const struct file_operations tracing_readme_fops = {
.llseek = generic_file_llseek,
};

+static void *saved_tgids_next(struct seq_file *m, void *v, loff_t *pos)
+{
+ int *ptr = v;
+
+ if (*pos || m->count)
+ ptr++;
+
+ (*pos)++;
+
+ for (; ptr <= &tgid_map[PID_MAX_DEFAULT]; ptr++) {
+ if (trace_find_tgid(*ptr))
+ return ptr;
+ }
+
+ return NULL;
+}
+
+static void *saved_tgids_start(struct seq_file *m, loff_t *pos)
+{
+ void *v;
+ loff_t l = 0;
+
+ if (!tgid_map)
+ return NULL;
+
+ v = &tgid_map[0];
+ while (l <= *pos) {
+ v = saved_tgids_next(m, v, &l);
+ if (!v)
+ return NULL;
+ }
+
+ return v;
+}
+
+static void saved_tgids_stop(struct seq_file *m, void *v)
+{
+}
+
+static int saved_tgids_show(struct seq_file *m, void *v)
+{
+ int pid = (int *)v - tgid_map;
+
+ seq_printf(m, "%d %d\n", pid, trace_find_tgid(pid));
+ return 0;
+}
+
+static const struct seq_operations tracing_saved_tgids_seq_ops = {
+ .start = saved_tgids_start,
+ .stop = saved_tgids_stop,
+ .next = saved_tgids_next,
+ .show = saved_tgids_show,
+};
+
+static int tracing_saved_tgids_open(struct inode *inode, struct file *filp)
+{
+ if (tracing_disabled)
+ return -ENODEV;
+
+ return seq_open(filp, &tracing_saved_tgids_seq_ops);
+}
+
+
+static const struct file_operations tracing_saved_tgids_fops = {
+ .open = tracing_saved_tgids_open,
+ .read = seq_read,
+ .llseek = seq_lseek,
+ .release = seq_release,
+};
+
static void *saved_cmdlines_next(struct seq_file *m, void *v, loff_t *pos)
{
unsigned int *ptr = v;
@@ -7945,6 +8015,9 @@ 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);
--
2.13.2
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