On Thu, Apr 9, 2020 at 9:22 PM Steven Rostedt <rostedt@xxxxxxxxxxx> wrote:
>
> On Tue, 25 Feb 2020 20:07:30 +0200
> "Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx> 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@xxxxxxxxx>
> > ---
> > 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);
> > +}
>
--
Tzvetomir (Ceco) Stoyanov
VMware Open Source Technology Center
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