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SubjectRe: [for-next][PATCH 5/7] tracing: Automatically mount tracefs on debugfs/tracing
On Wed, Feb 04, 2015 at 09:34:25AM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Red Hat)" <rostedt@goodmis.org>
>
> As tools currently rely on the tracing directory in debugfs, we can not
> just created a tracefs infrastructure and expect sysadmins to mount
> the new tracefs to have their old tools work.
>
> Instead, the debugfs tracing directory is still created and the tracefs
> file system is mounted there when the debugfs filesystem is mounted.
>
> No longer does the tracing infrastructure update the debugfs file system,
> but instead interacts with the tracefs file system. But now, it still
> appears to the user like nothing changed, except you also have the feature
> of mounting just the tracing system without needing all of debugfs!

One question. Is it possible to have both of the old
/sys/kernel/debug/tracing and new /sys/kernel/tracing directories?


>
> Cc: Al Viro <viro@zeniv.linux.org.uk>
> Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
> ---
> kernel/trace/trace.c | 36 +++++++++++++++++++++++++++++++++---
> 1 file changed, 33 insertions(+), 3 deletions(-)
>
> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
> index 6c4739bee4bb..b4aa936509d2 100644
> --- a/kernel/trace/trace.c
> +++ b/kernel/trace/trace.c
> @@ -32,6 +32,7 @@
> #include <linux/splice.h>
> #include <linux/kdebug.h>
> #include <linux/string.h>
> +#include <linux/mount.h>
> #include <linux/rwsem.h>
> #include <linux/slab.h>
> #include <linux/ctype.h>
> @@ -6535,6 +6536,28 @@ init_tracer_tracefs(struct trace_array *tr, struct dentry *d_tracer)
>
> }
>
> +static struct vfsmount *trace_automount(void *ingore)
> +{
> + struct vfsmount *mnt;
> + struct file_system_type *type;
> +
> + /*
> + * To maintain backward compatibility for tools that mount
> + * debugfs to get to the tracing facility, tracefs is automatically
> + * mounted to the debugfs/tracing directory.
> + */
> + type = get_fs_type("tracefs");
> + if (!type)
> + return NULL;
> + mnt = vfs_kern_mount(type, 0, "tracefs", NULL);
> + put_filesystem(type);
> + if (IS_ERR(mnt))
> + return NULL;
> + mntget(mnt);
> +
> + return mnt;
> +}
> +
> /**
> * tracing_init_dentry - initialize top level trace array
> *
> @@ -6546,14 +6569,21 @@ struct dentry *tracing_init_dentry(void)
> {
> struct trace_array *tr = &global_trace;
>
> + /* The top level trace array uses NULL as parent */
> if (tr->dir)
> - return tr->dir;
> + return NULL;
>
> if (WARN_ON(!debugfs_initialized()))
> return ERR_PTR(-ENODEV);
>
> - tr->dir = debugfs_create_dir("tracing", NULL);
> -
> + /*
> + * As there may still be users that expect the tracing
> + * files to exist in debugfs/tracing, we must automount
> + * the tracefs file system there, so older tools still
> + * work with the newer kerenl.

s/kerenl/kernel/

Thanks,
Namhyung


> + */
> + tr->dir = debugfs_create_automount("tracing", NULL,
> + trace_automount, NULL);
> if (!tr->dir) {
> pr_warn_once("Could not create debugfs directory 'tracing'\n");
> return ERR_PTR(-ENOMEM);
> --
> 2.1.4
>
>
> --
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