[v4,1/4] trace-cmd: Add new tracefs APIs for checking if a ftrace file / directory exists
diff mbox series

Message ID 20200225180733.89344-2-tz.stoyanov@gmail.com
State Superseded
Delegated to: Steven Rostedt
Headers show
Series
  • Extend coverage of "trace-cmd reset" command
Related show

Commit Message

Tzvetomir Stoyanov (VMware) Feb. 25, 2020, 6:07 p.m. UTC
Some ftrace files and directories are optional, depending on specific kernel configuration or version.
It is a good practice to check if the file / directory exist, before trying to access it. There are a lot of places in trace-cmd implementation with such checks.
The new libtracefs APIs can be used for this, they are ftarce instance aware:
 bool tracefs_file_exist(struct tracefs_instance *instance, char *name);
 bool tracefs_dir_exist(struct tracefs_instance *instance, char *name);

Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
---
 include/tracefs/tracefs.h      |  3 +++
 lib/tracefs/tracefs-instance.c | 49 +++++++++++++++++++++++++++++++++-
 2 files changed, 51 insertions(+), 1 deletion(-)

Comments

Steven Rostedt April 9, 2020, 6:22 p.m. UTC | #1
On Tue, 25 Feb 2020 20:07:30 +0200
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:

> Some ftrace files and directories are optional, depending on specific kernel configuration or version.
> It is a good practice to check if the file / directory exist, before trying to access it. There are a lot of places in trace-cmd implementation with such checks.
> The new libtracefs APIs can be used for this, they are ftarce instance aware:
>  bool tracefs_file_exist(struct tracefs_instance *instance, char *name);
>  bool tracefs_dir_exist(struct tracefs_instance *instance, char *name);
> 
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
> ---
>  include/tracefs/tracefs.h      |  3 +++
>  lib/tracefs/tracefs-instance.c | 49 +++++++++++++++++++++++++++++++++-
>  2 files changed, 51 insertions(+), 1 deletion(-)
> 
> diff --git a/include/tracefs/tracefs.h b/include/tracefs/tracefs.h
> index 85690b66..bc8bebcb 100644
> --- a/include/tracefs/tracefs.h
> +++ b/include/tracefs/tracefs.h
> @@ -33,6 +33,9 @@ int tracefs_instance_file_write(struct tracefs_instance *instance,
>  char *tracefs_instance_file_read(struct tracefs_instance *instance,
>  				 char *file, int *psize);
>  
> +bool tracefs_file_exist(struct tracefs_instance *instance, char *name);
> +bool tracefs_dir_exist(struct tracefs_instance *instance, char *name);
> +
>  /* events */
>  void tracefs_list_free(char **list);
>  char **tracefs_event_systems(const char *tracing_dir);
> diff --git a/lib/tracefs/tracefs-instance.c b/lib/tracefs/tracefs-instance.c
> index b96ab61c..67123e7c 100644
> --- a/lib/tracefs/tracefs-instance.c
> +++ b/lib/tracefs/tracefs-instance.c
> @@ -13,7 +13,7 @@
>  #include <errno.h>
>  #include <sys/stat.h>
>  #include <fcntl.h>
> -
> +#include <linux/limits.h>
>  #include "tracefs.h"
>  #include "tracefs-local.h"
>  
> @@ -247,3 +247,50 @@ char *tracefs_instance_file_read(struct tracefs_instance *instance,
>  
>  	return buf;
>  }
> +
> +static bool check_file_exist(struct tracefs_instance *instance,
> +			     char *name, bool dir)
> +{
> +	char file[PATH_MAX];
> +	struct stat st;
> +	char *path;
> +	int ret;
> +
> +	path = tracefs_instance_get_dir(instance);
> +	snprintf(file, PATH_MAX, "%s/%s", path, name);
> +	tracefs_put_tracing_file(path);
> +	ret = stat(file, &st);
> +	if (ret < 0)
> +		return false;
> +
> +	if (dir && !S_ISDIR(st.st_mode))
> +		return false;
> +	if (!dir && S_ISDIR(st.st_mode))
> +		return false;
> +
> +	return true;

BTW, the above can be converted to just:

	return !dir == !S_ISDIR(st.st_mode);


> +}
> +
> +/**
> + * tracefs_file_exist - Check if a file with given name exists in given instance
> + * @instance: ftrace instance, can be NULL for the top instance
> + * @name: name of the file
> + *
> + * Returns true if the file exists, false otherwise

Probably should comment that this will return false if the "file" exists
but is a directory.

Is there any reason we would not want to return true here if it was a
directory? A directory is just another kind of "file" (in the Unix world).

-- Steve

> + */
> +bool tracefs_file_exist(struct tracefs_instance *instance, char *name)
> +{
> +	return check_file_exist(instance, name, false);
> +}
> +
> +/**
> + * tracefs_dir_exist - Check if a directory with given name exists in given instance
> + * @instance: ftrace instance, can be NULL for the top instance
> + * @name: name of the directory
> + *
> + * Returns true if the directory exists, false otherwise
> + */
> +bool tracefs_dir_exist(struct tracefs_instance *instance, char *name)
> +{
> +	return check_file_exist(instance, name, true);
> +}
Tzvetomir Stoyanov (VMware) April 13, 2020, 6:52 a.m. UTC | #2
On Thu, Apr 9, 2020 at 9:22 PM Steven Rostedt <rostedt@goodmis.org> wrote:
>
> On Tue, 25 Feb 2020 20:07:30 +0200
> "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@gmail.com> wrote:
>
> > Some ftrace files and directories are optional, depending on specific kernel configuration or version.
> > It is a good practice to check if the file / directory exist, before trying to access it. There are a lot of places in trace-cmd implementation with such checks.
> > The new libtracefs APIs can be used for this, they are ftarce instance aware:
> >  bool tracefs_file_exist(struct tracefs_instance *instance, char *name);
> >  bool tracefs_dir_exist(struct tracefs_instance *instance, char *name);
> >
> > Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@gmail.com>
> > ---
> >  include/tracefs/tracefs.h      |  3 +++
> >  lib/tracefs/tracefs-instance.c | 49 +++++++++++++++++++++++++++++++++-
> >  2 files changed, 51 insertions(+), 1 deletion(-)
> >
> > diff --git a/include/tracefs/tracefs.h b/include/tracefs/tracefs.h
> > index 85690b66..bc8bebcb 100644
> > --- a/include/tracefs/tracefs.h
> > +++ b/include/tracefs/tracefs.h
> > @@ -33,6 +33,9 @@ int tracefs_instance_file_write(struct tracefs_instance *instance,
> >  char *tracefs_instance_file_read(struct tracefs_instance *instance,
> >                                char *file, int *psize);
> >
> > +bool tracefs_file_exist(struct tracefs_instance *instance, char *name);
> > +bool tracefs_dir_exist(struct tracefs_instance *instance, char *name);
> > +
> >  /* events */
> >  void tracefs_list_free(char **list);
> >  char **tracefs_event_systems(const char *tracing_dir);
> > diff --git a/lib/tracefs/tracefs-instance.c b/lib/tracefs/tracefs-instance.c
> > index b96ab61c..67123e7c 100644
> > --- a/lib/tracefs/tracefs-instance.c
> > +++ b/lib/tracefs/tracefs-instance.c
> > @@ -13,7 +13,7 @@
> >  #include <errno.h>
> >  #include <sys/stat.h>
> >  #include <fcntl.h>
> > -
> > +#include <linux/limits.h>
> >  #include "tracefs.h"
> >  #include "tracefs-local.h"
> >
> > @@ -247,3 +247,50 @@ char *tracefs_instance_file_read(struct tracefs_instance *instance,
> >
> >       return buf;
> >  }
> > +
> > +static bool check_file_exist(struct tracefs_instance *instance,
> > +                          char *name, bool dir)
> > +{
> > +     char file[PATH_MAX];
> > +     struct stat st;
> > +     char *path;
> > +     int ret;
> > +
> > +     path = tracefs_instance_get_dir(instance);
> > +     snprintf(file, PATH_MAX, "%s/%s", path, name);
> > +     tracefs_put_tracing_file(path);
> > +     ret = stat(file, &st);
> > +     if (ret < 0)
> > +             return false;
> > +
> > +     if (dir && !S_ISDIR(st.st_mode))
> > +             return false;
> > +     if (!dir && S_ISDIR(st.st_mode))
> > +             return false;
> > +
> > +     return true;
>
> BTW, the above can be converted to just:
>
>         return !dir == !S_ISDIR(st.st_mode);
>
>
> > +}
> > +
> > +/**
> > + * tracefs_file_exist - Check if a file with given name exists in given instance
> > + * @instance: ftrace instance, can be NULL for the top instance
> > + * @name: name of the file
> > + *
> > + * Returns true if the file exists, false otherwise
>
> Probably should comment that this will return false if the "file" exists
> but is a directory.
>
> Is there any reason we would not want to return true here if it was a
> directory? A directory is just another kind of "file" (in the Unix world).
>

The use case of the API is to check if a given file exists in tracefs, before
writing to / reading from it. If the user expects file, but it is a directory -
the operation will fail. We can think of adding additional input parameter
to the API, to let the user specify the desired behavior of the API ?
Something like :
bool tracefs_file_exist(struct tracefs_instance *instance, char *name,
bool any);


> -- Steve
>
> > + */
> > +bool tracefs_file_exist(struct tracefs_instance *instance, char *name)
> > +{
> > +     return check_file_exist(instance, name, false);
> > +}
> > +
> > +/**
> > + * tracefs_dir_exist - Check if a directory with given name exists in given instance
> > + * @instance: ftrace instance, can be NULL for the top instance
> > + * @name: name of the directory
> > + *
> > + * Returns true if the directory exists, false otherwise
> > + */
> > +bool tracefs_dir_exist(struct tracefs_instance *instance, char *name)
> > +{
> > +     return check_file_exist(instance, name, true);
> > +}
>

Patch
diff mbox series

diff --git a/include/tracefs/tracefs.h b/include/tracefs/tracefs.h
index 85690b66..bc8bebcb 100644
--- a/include/tracefs/tracefs.h
+++ b/include/tracefs/tracefs.h
@@ -33,6 +33,9 @@  int tracefs_instance_file_write(struct tracefs_instance *instance,
 char *tracefs_instance_file_read(struct tracefs_instance *instance,
 				 char *file, int *psize);
 
+bool tracefs_file_exist(struct tracefs_instance *instance, char *name);
+bool tracefs_dir_exist(struct tracefs_instance *instance, char *name);
+
 /* events */
 void tracefs_list_free(char **list);
 char **tracefs_event_systems(const char *tracing_dir);
diff --git a/lib/tracefs/tracefs-instance.c b/lib/tracefs/tracefs-instance.c
index b96ab61c..67123e7c 100644
--- a/lib/tracefs/tracefs-instance.c
+++ b/lib/tracefs/tracefs-instance.c
@@ -13,7 +13,7 @@ 
 #include <errno.h>
 #include <sys/stat.h>
 #include <fcntl.h>
-
+#include <linux/limits.h>
 #include "tracefs.h"
 #include "tracefs-local.h"
 
@@ -247,3 +247,50 @@  char *tracefs_instance_file_read(struct tracefs_instance *instance,
 
 	return buf;
 }
+
+static bool check_file_exist(struct tracefs_instance *instance,
+			     char *name, bool dir)
+{
+	char file[PATH_MAX];
+	struct stat st;
+	char *path;
+	int ret;
+
+	path = tracefs_instance_get_dir(instance);
+	snprintf(file, PATH_MAX, "%s/%s", path, name);
+	tracefs_put_tracing_file(path);
+	ret = stat(file, &st);
+	if (ret < 0)
+		return false;
+
+	if (dir && !S_ISDIR(st.st_mode))
+		return false;
+	if (!dir && S_ISDIR(st.st_mode))
+		return false;
+
+	return true;
+}
+
+/**
+ * tracefs_file_exist - Check if a file with given name exists in given instance
+ * @instance: ftrace instance, can be NULL for the top instance
+ * @name: name of the file
+ *
+ * Returns true if the file exists, false otherwise
+ */
+bool tracefs_file_exist(struct tracefs_instance *instance, char *name)
+{
+	return check_file_exist(instance, name, false);
+}
+
+/**
+ * tracefs_dir_exist - Check if a directory with given name exists in given instance
+ * @instance: ftrace instance, can be NULL for the top instance
+ * @name: name of the directory
+ *
+ * Returns true if the directory exists, false otherwise
+ */
+bool tracefs_dir_exist(struct tracefs_instance *instance, char *name)
+{
+	return check_file_exist(instance, name, true);
+}