ftrace: add readpos to struct trace_seq; add trace_seq_to_user()

Refactor code from tracing_read_pipe() and create trace_seq_to_user().
Moved trace_seq_reset() call before iter->trace->read() call so that
when all leftover data is returned, trace_seq is reset automatically.

Signed-off-by: Pekka Paalanen <pq@iki.fi>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

2 files changed, 39 insertions, 37 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index c232d8248a09..82ced406aacf 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -400,6 +400,26 @@ static void
 trace_seq_reset(struct trace_seq *s)
 {
         s->len = 0;
+        s->readpos = 0;
+}
+
+ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf, size_t cnt)
+{
+        int len;
+        int ret;
+
+        if (s->len <= s->readpos)
+                return -EBUSY;
+
+        len = s->len - s->readpos;
+        if (cnt > len)
+                cnt = len;
+        ret = copy_to_user(ubuf, s->buffer + s->readpos, cnt);
+        if (ret)
+                return -EFAULT;
+
+        s->readpos += len;
+        return cnt;
 }
 
 static void
@@ -2361,46 +2381,32 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
         struct trace_iterator *iter = filp->private_data;
         struct trace_array_cpu *data;
         static cpumask_t mask;
-        static int start;
         unsigned long flags;
 #ifdef CONFIG_FTRACE
         int ftrace_save;
 #endif
-        int read = 0;
         int cpu;
-        int len;
-        int ret;
+        ssize_t sret;
 
         /* return any leftover data */
-        if (iter->seq.len > start) {
-                len = iter->seq.len - start;
-                if (cnt > len)
-                        cnt = len;
-                ret = copy_to_user(ubuf, iter->seq.buffer + start, cnt);
-                if (ret)
-                        cnt = -EFAULT;
-
-                start += len;
+        sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
+        if (sret != -EBUSY)
+                return sret;
+        sret = 0;
 
-                return cnt;
-        }
+        trace_seq_reset(&iter->seq);
 
         mutex_lock(&trace_types_lock);
         if (iter->trace->read) {
-                ret = iter->trace->read(iter, filp, ubuf, cnt, ppos);
-                if (ret) {
-                        read = ret;
+                sret = iter->trace->read(iter, filp, ubuf, cnt, ppos);
+                if (sret)
                         goto out;
-                }
         }
 
-        trace_seq_reset(&iter->seq);
-        start = 0;
-
         while (trace_empty(iter)) {
 
                 if ((filp->f_flags & O_NONBLOCK)) {
-                        read = -EAGAIN;
+                        sret = -EAGAIN;
                         goto out;
                 }
 
@@ -2426,7 +2432,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
                 iter->tr->waiter = NULL;
 
                 if (signal_pending(current)) {
-                        read = -EINTR;
+                        sret = -EINTR;
                         goto out;
                 }
 
@@ -2496,6 +2502,7 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
         }
 
         while (find_next_entry_inc(iter) != NULL) {
+                int ret;
                 int len = iter->seq.len;
 
                 ret = print_trace_line(iter);
@@ -2526,24 +2533,16 @@ tracing_read_pipe(struct file *filp, char __user *ubuf,
         local_irq_restore(flags);
 
         /* Now copy what we have to the user */
-        read = iter->seq.len;
-        if (read > cnt)
-                read = cnt;
-
-        ret = copy_to_user(ubuf, iter->seq.buffer, read);
-
-        if (read < iter->seq.len)
-                start = read;
-        else
+        sret = trace_seq_to_user(&iter->seq, ubuf, cnt);
+        if (iter->seq.readpos >= iter->seq.len)
                 trace_seq_reset(&iter->seq);
-
-        if (ret)
-                read = -EFAULT;
+        if (sret == -EBUSY)
+                sret = 0;
 
 out:
         mutex_unlock(&trace_types_lock);
 
-        return read;
+        return sret;
 }
 
 static ssize_t
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index ee53d706066f..8845033ab49d 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -155,6 +155,7 @@ struct tracer {
 struct trace_seq {
         unsigned char           buffer[PAGE_SIZE];
         unsigned int            len;
+        unsigned int            readpos;
 };
 
 /*
@@ -301,6 +302,8 @@ extern int trace_selftest_startup_sched_switch(struct tracer *trace,
 
 extern void *head_page(struct trace_array_cpu *data);
 extern int trace_seq_printf(struct trace_seq *s, const char *fmt, ...);
+extern ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf,
+                                 size_t cnt);
 extern long ns2usecs(cycle_t nsec);
 
 extern unsigned long trace_flags;