tracing: splice support for tracing_pipe

Added and implemented tracing_pipe_fops->splice_read(). This allows
userspace programs to get tracing data more efficiently.

Signed-off-by: Eduard - Gabriel Munteanu <eduard.munteanu@linux360.ro>
Signed-off-by: Steven Rostedt <srostedt@redhat.com>

1 files changed, 136 insertions, 0 deletions

diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
index 5b1e9a9e9906..9e29fdb0dfe5 100644
--- a/kernel/trace/trace.c
+++ b/kernel/trace/trace.c
@@ -31,6 +31,7 @@
 #include <linux/fs.h>
 #include <linux/kprobes.h>
 #include <linux/writeback.h>
+#include <linux/splice.h>
 
 #include <linux/stacktrace.h>
 #include <linux/ring_buffer.h>
@@ -364,6 +365,25 @@ ssize_t trace_seq_to_user(struct trace_seq *s, char __user *ubuf, size_t cnt)
         return cnt;
 }
 
+ssize_t trace_seq_to_buffer(struct trace_seq *s, void *buf, size_t cnt)
+{
+        int len;
+        void *ret;
+
+        if (s->len <= s->readpos)
+                return -EBUSY;
+
+        len = s->len - s->readpos;
+        if (cnt > len)
+                cnt = len;
+        ret = memcpy(buf, s->buffer + s->readpos, cnt);
+        if (!ret)
+                return -EFAULT;
+
+        s->readpos += len;
+        return cnt;
+}
+
 static void
 trace_print_seq(struct seq_file *m, struct trace_seq *s)
 {
@@ -2493,6 +2513,121 @@ out:
         return sret;
 }
 
+static void tracing_pipe_buf_release(struct pipe_inode_info *pipe,
+                                     struct pipe_buffer *buf)
+{
+        __free_page(buf->page);
+}
+
+static void tracing_spd_release_pipe(struct splice_pipe_desc *spd,
+                                     unsigned int idx)
+{
+        __free_page(spd->pages[idx]);
+}
+
+static struct pipe_buf_operations tracing_pipe_buf_ops = {
+        .can_merge = 0,
+        .map = generic_pipe_buf_map,
+        .unmap = generic_pipe_buf_unmap,
+        .confirm = generic_pipe_buf_confirm,
+        .release = tracing_pipe_buf_release,
+        .steal = generic_pipe_buf_steal,
+        .get = generic_pipe_buf_get,
+};
+
+static ssize_t tracing_splice_read_pipe(struct file *filp,
+                                        loff_t *ppos,
+                                        struct pipe_inode_info *pipe,
+                                        size_t len,
+                                        unsigned int flags)
+{
+        struct page *pages[PIPE_BUFFERS];
+        struct partial_page partial[PIPE_BUFFERS];
+        struct trace_iterator *iter = filp->private_data;
+        struct splice_pipe_desc spd = {
+                .pages = pages,
+                .partial = partial,
+                .nr_pages = 0, /* This gets updated below. */
+                .flags = flags,
+                .ops = &tracing_pipe_buf_ops,
+                .spd_release = tracing_spd_release_pipe,
+        };
+        ssize_t ret;
+        size_t count, rem;
+        unsigned int i;
+
+        mutex_lock(&trace_types_lock);
+
+        if (iter->trace->splice_read) {
+                ret = iter->trace->splice_read(iter, filp,
+                                               ppos, pipe, len, flags);
+                if (ret)
+                        goto out;
+        }
+
+        ret = tracing_wait_pipe(filp);
+        if (ret <= 0)
+                goto out;
+
+        if (!iter->ent && !find_next_entry_inc(iter)) {
+                ret = -EFAULT;
+                goto out;
+        }
+
+        /* Fill as many pages as possible. */
+        for (i = 0, rem = len; i < PIPE_BUFFERS && rem; i++) {
+                pages[i] = alloc_page(GFP_KERNEL);
+
+                /* Seq buffer is page-sized, exactly what we need. */
+                for (;;) {
+                        count = iter->seq.len;
+                        ret = print_trace_line(iter);
+                        count = iter->seq.len - count;
+                        if (rem < count) {
+                                rem = 0;
+                                iter->seq.len -= count;
+                                break;
+                        }
+                        if (ret == TRACE_TYPE_PARTIAL_LINE) {
+                                iter->seq.len -= count;
+                                break;
+                        }
+
+                        trace_consume(iter);
+                        rem -= count;
+                        if (!find_next_entry_inc(iter)) {
+                                rem = 0;
+                                iter->ent = NULL;
+                                break;
+                        }
+                }
+
+                /* Copy the data into the page, so we can start over. */
+                ret = trace_seq_to_buffer(&iter->seq,
+                                          page_address(pages[i]),
+                                          iter->seq.len);
+                if (ret < 0) {
+                        __free_page(pages[i]);
+                        break;
+                }
+                partial[i].offset = 0;
+                partial[i].len = iter->seq.len;
+
+                trace_seq_reset(&iter->seq);
+        }
+
+        mutex_unlock(&trace_types_lock);
+
+        spd.nr_pages = i;
+
+        return splice_to_pipe(pipe, &spd);
+
+out:
+        mutex_unlock(&trace_types_lock);
+
+        return ret;
+}
+
 static ssize_t
 tracing_entries_read(struct file *filp, char __user *ubuf,
                      size_t cnt, loff_t *ppos)
@@ -2656,6 +2791,7 @@ static struct file_operations tracing_pipe_fops = {
         .open           = tracing_open_pipe,
         .poll           = tracing_poll_pipe,
         .read           = tracing_read_pipe,
+        .splice_read    = tracing_splice_read_pipe,
         .release        = tracing_release_pipe,
 };