@@ -26,4 +26,6 @@ struct trace_buffer_meta {
__u32 meta_struct_len; /* Len of this struct */
};
+#define TRACE_MMAP_IOCTL_GET_READER _IO('T', 0x1)
+
#endif /* _UAPI_TRACE_MMAP_H_ */
@@ -8590,15 +8590,31 @@ tracing_buffers_splice_read(struct file *file, loff_t *ppos,
return ret;
}
-/* An ioctl call with cmd 0 to the ring buffer file will wake up all waiters */
static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned long arg)
{
struct ftrace_buffer_info *info = file->private_data;
struct trace_iterator *iter = &info->iter;
+ int err;
- if (cmd)
- return -ENOIOCTLCMD;
+ if (cmd == TRACE_MMAP_IOCTL_GET_READER) {
+ if (!(file->f_flags & O_NONBLOCK)) {
+ err = ring_buffer_wait(iter->array_buffer->buffer,
+ iter->cpu_file,
+ iter->tr->buffer_percent);
+ if (err)
+ return err;
+ }
+ return ring_buffer_map_get_reader(iter->array_buffer->buffer,
+ iter->cpu_file);
+ } else if (cmd) {
+ return -ENOTTY;
+ }
+
+ /*
+ * An ioctl call with cmd 0 to the ring buffer file will wake up all
+ * waiters
+ */
mutex_lock(&trace_types_lock);
iter->wait_index++;
@@ -8611,6 +8627,62 @@ static long tracing_buffers_ioctl(struct file *file, unsigned int cmd, unsigned
return 0;
}
+static vm_fault_t tracing_buffers_mmap_fault(struct vm_fault *vmf)
+{
+ struct ftrace_buffer_info *info = vmf->vma->vm_file->private_data;
+ struct trace_iterator *iter = &info->iter;
+ vm_fault_t ret = VM_FAULT_SIGBUS;
+ struct page *page;
+
+ page = ring_buffer_map_fault(iter->array_buffer->buffer, iter->cpu_file,
+ vmf->pgoff);
+ if (!page)
+ return ret;
+
+ get_page(page);
+ vmf->page = page;
+ vmf->page->mapping = vmf->vma->vm_file->f_mapping;
+ vmf->page->index = vmf->pgoff;
+
+ return 0;
+}
+
+static void tracing_buffers_mmap_close(struct vm_area_struct *vma)
+{
+ struct ftrace_buffer_info *info = vma->vm_file->private_data;
+ struct trace_iterator *iter = &info->iter;
+
+ ring_buffer_unmap(iter->array_buffer->buffer, iter->cpu_file);
+}
+
+static void tracing_buffers_mmap_open(struct vm_area_struct *vma)
+{
+ struct ftrace_buffer_info *info = vma->vm_file->private_data;
+ struct trace_iterator *iter = &info->iter;
+
+ WARN_ON(ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file));
+}
+
+static const struct vm_operations_struct tracing_buffers_vmops = {
+ .open = tracing_buffers_mmap_open,
+ .close = tracing_buffers_mmap_close,
+ .fault = tracing_buffers_mmap_fault,
+};
+
+static int tracing_buffers_mmap(struct file *filp, struct vm_area_struct *vma)
+{
+ struct ftrace_buffer_info *info = filp->private_data;
+ struct trace_iterator *iter = &info->iter;
+
+ if (vma->vm_flags & VM_WRITE)
+ return -EPERM;
+
+ vm_flags_mod(vma, VM_DONTCOPY | VM_DONTDUMP, VM_MAYWRITE);
+ vma->vm_ops = &tracing_buffers_vmops;
+
+ return ring_buffer_map(iter->array_buffer->buffer, iter->cpu_file);
+}
+
static const struct file_operations tracing_buffers_fops = {
.open = tracing_buffers_open,
.read = tracing_buffers_read,
@@ -8619,6 +8691,7 @@ static const struct file_operations tracing_buffers_fops = {
.splice_read = tracing_buffers_splice_read,
.unlocked_ioctl = tracing_buffers_ioctl,
.llseek = no_llseek,
+ .mmap = tracing_buffers_mmap,
};
static ssize_t
Currently, user-space extracts data from the ring-buffer via splice, which is handy for storage or network sharing. However, due to splice limitations, it is imposible to do real-time analysis without a copy. A solution for that problem is to let the user-space map the ring-buffer directly. The mapping is exposed via the per-CPU file trace_pipe_raw. The first element of the mapping is the meta-page. It is followed by each bpage constituting the ring-buffer, ordered by their unique page ID: * Meta-page -- include/uapi/linux/trace_mmap.h for a description * buffer-page ID 0 * buffer-page ID 1 ... It is therefore easy to translate a buffer page ID into an offset in the mapping: reader_id = meta->reader->id; reader_offset = meta->meta_page_size + reader_id * meta->bpage_size; When new data is available, the mapper must call a newly introduced ioctl: TRACE_MMAP_IOCTL_GET_READER. This will update the Meta-page reader ID to point to the next reader containing unread data. Signed-off-by: Vincent Donnefort <vdonnefort@google.com>