Provides a generic read and write implementation to save/read u64 values
from a file on tracefs. The trace_ull_config structure defines where to
read/write the value, the min and the max acceptable values, and a lock
to protect the write.
Cc: Jonathan Corbet <corbet@xxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: Ingo Molnar <mingo@xxxxxxxxxx>
Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Alexandre Chartre <alexandre.chartre@xxxxxxxxxx>
Cc: Clark Willaims <williams@xxxxxxxxxx>
Cc: John Kacur <jkacur@xxxxxxxxxx>
Cc: Juri Lelli <juri.lelli@xxxxxxxxxx>
Cc: linux-doc@xxxxxxxxxxxxxxx
Cc: linux-kernel@xxxxxxxxxxxxxxx
Signed-off-by: Daniel Bristot de Oliveira <bristot@xxxxxxxxxx>
---
kernel/trace/trace.c | 88 +++++++++++++++++++++++++++++++++++++++++++-
kernel/trace/trace.h | 20 ++++++++++
2 files changed, 107 insertions(+), 1 deletion(-)
diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5c777627212f..61713a08bb79 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -7185,7 +7185,6 @@ static int snapshot_raw_open(struct inode *inode, struct file *filp)
#endif /* CONFIG_TRACER_SNAPSHOT */
-
static const struct file_operations tracing_thresh_fops = {
.open = tracing_open_generic,
.read = tracing_thresh_read,
@@ -7287,6 +7286,93 @@ static const struct file_operations snapshot_raw_fops = {
#endif /* CONFIG_TRACER_SNAPSHOT */
+/*
+ * trace_ull_config_write - Generic write function to save u64 value
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * This function provides a generic write implementation to save u64 values
+ * from a file on tracefs. The filp->private_data must point to a
+ * trace_ull_config structure that defines where to write the value, the
+ * min and the max acceptable values, and a lock to protect the write.
+ */
+ssize_t
+trace_ull_config_write(struct file *filp, const char __user *ubuf, size_t cnt,
+ loff_t *ppos)
+{
+ struct trace_ull_config *config = filp->private_data;
+ u64 val;
+ int err;
+
+ if (!config)
+ return -EFAULT;
+
+ err = kstrtoull_from_user(ubuf, cnt, 10, &val);
+ if (err)
+ return err;
+
+ if (config->lock)
+ mutex_lock(config->lock);
+
+ if (config->min && val < *config->min)
+ err = -EINVAL;
+
+ if (config->max && val > *config->max)
+ err = -EINVAL;
+
+ if (!err)
+ *config->val = val;
+
+ if (config->lock)
+ mutex_unlock(config->lock);
+
+ if (err)
+ return err;
+
+ return cnt;
+}
+
+/*
+ * trace_ull_config_read - Generic write function to read u64 value via tracefs
+ * @filp: The active open file structure
+ * @ubuf: The userspace provided buffer to read value into
+ * @cnt: The maximum number of bytes to read
+ * @ppos: The current "file" position
+ *
+ * This function provides a generic read implementation to read a u64 value
+ * from a file on tracefs. The filp->private_data must point to a
+ * trace_ull_config structure with valid data.
+ */
+ssize_t
+trace_ull_config_read(struct file *filp, char __user *ubuf, size_t cnt,
+ loff_t *ppos)
+{
+ struct trace_ull_config *config = filp->private_data;
+ char buf[ULL_STR_SIZE];
+ u64 val;
+ int len;
+
+ if (!config)
+ return -EFAULT;
+
+ val = *config->val;
+
+ if (cnt > sizeof(buf))
+ cnt = sizeof(buf);
+
+ len = snprintf(buf, sizeof(buf), "%llu\n", val);
+
+ return simple_read_from_buffer(ubuf, cnt, ppos, buf, len);
+}
+
+const struct file_operations trace_ull_config_fops = {
+ .open = tracing_open_generic,
+ .read = trace_ull_config_read,
+ .write = trace_ull_config_write,
+};
+
#define TRACING_LOG_ERRS_MAX 8
#define TRACING_LOG_LOC_MAX 128
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index a6446c03cfbc..5a47c27b768f 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -1929,4 +1929,24 @@ static inline bool is_good_name(const char *name)
return true;
}
+/*
+ * This is a generic way to read and write a u64 config value from a file
+ * in tracefs.
+ *
+ * The value is stored on the variable pointed by *val. The value needs
+ * to be at least *min and at most *max. The write is protected by an
+ * existing *lock.
+ */
+struct trace_ull_config {
+ struct mutex *lock;
+ u64 *val;
+ u64 *min;
+ u64 *max;
+};
+
+#define ULL_STR_SIZE 22 /* 20 digits max */
+
+extern const struct file_operations trace_ull_config_fops;
+
+
#endif /* _LINUX_KERNEL_TRACE_H */
--
2.26.3
