On Thu, 7 Jan 2021 10:32:46 +0200
"Tzvetomir Stoyanov (VMware)" <tz.stoyanov@xxxxxxxxx> wrote:
> These new APIs can be used to enable / disable tracing in given ftrace
> instance:
> tracefs_trace_is_on();
> tracefs_trace_on();
> tracefs_trace_off();
> tracefs_trace_on_fd();
> tracefs_trace_off_fd();
>
> Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@xxxxxxxxx>
> ---
> include/tracefs.h | 6 +++
> src/Makefile | 1 +
> src/tracefs-tools.c | 123 ++++++++++++++++++++++++++++++++++++++++++++
> 3 files changed, 130 insertions(+)
> create mode 100644 src/tracefs-tools.c
>
> diff --git a/include/tracefs.h b/include/tracefs.h
> index 460fa4c..bc799c7 100644
> --- a/include/tracefs.h
> +++ b/include/tracefs.h
> @@ -40,6 +40,12 @@ bool tracefs_instance_exists(const char *name);
> bool tracefs_file_exists(struct tracefs_instance *instance, char *name);
> bool tracefs_dir_exists(struct tracefs_instance *instance, char *name);
>
> +int tracefs_trace_is_on(struct tracefs_instance *instance);
> +int tracefs_trace_on(struct tracefs_instance *instance);
> +int tracefs_trace_off(struct tracefs_instance *instance);
> +int tracefs_trace_on_fd(int fd);
> +int tracefs_trace_off_fd(int fd);
> +
> /* events */
> void tracefs_list_free(char **list);
> char **tracefs_event_systems(const char *tracing_dir);
> diff --git a/src/Makefile b/src/Makefile
> index 3f64905..dabdbb4 100644
> --- a/src/Makefile
> +++ b/src/Makefile
> @@ -6,6 +6,7 @@ OBJS =
> OBJS += tracefs-utils.o
> OBJS += tracefs-instance.o
> OBJS += tracefs-events.o
> +OBJS += tracefs-tools.o
>
> OBJS := $(OBJS:%.o=$(bdir)/%.o)
> DEPS := $(OBJS:$(bdir)/%.o=$(bdir)/.%.d)
> diff --git a/src/tracefs-tools.c b/src/tracefs-tools.c
> new file mode 100644
> index 0000000..89e2d6d
> --- /dev/null
> +++ b/src/tracefs-tools.c
> @@ -0,0 +1,123 @@
> +// SPDX-License-Identifier: LGPL-2.1
> +/*
> + * Copyright (C) 2008, 2009, 2010 Red Hat Inc, Steven Rostedt <srostedt@xxxxxxxxxx>
> + *
> + * Updates:
> + * Copyright (C) 2021, VMware, Tzvetomir Stoyanov <tz.stoyanov@xxxxxxxxx>
> + *
> + */
> +#include <stdlib.h>
> +#include <unistd.h>
> +#include <fcntl.h>
> +
> +#include "tracefs.h"
> +#include "tracefs-local.h"
> +
> +#define TRACE_CTRL "tracing_on"
> +
> +static int trace_on_off(int fd, bool on)
> +{
> + int ret;
> +
> + if (on)
> + ret = write(fd, "1", 1);
> + else
> + ret = write(fd, "0", 1);
Instead of having both blocks of the if statement call write, it would be
simpler to have:
const char *val = on ? "1" : "0";
ret = write(fd, val, 1);
> +
> + if (ret == 1)
> + return 0;
> +
> + return -1;
> +}
> +
> +static int trace_on_off_file(struct tracefs_instance *instance, bool on)
> +{
> + int ret;
> + int fd;
> +
> + fd = tracefs_instance_file_open(instance, TRACE_CTRL, O_WRONLY);
> + if (fd < 0)
> + return -1;
> + ret = trace_on_off(fd, on);
> + close(fd);
> +
> + return ret;
> +}
> +
> +/**
> + * tracefs_trace_is_on - Check if writing traces to the ring buffer is enabled
> + * @instance: ftrace instance, can be NULL for the top instance
> + *
> + * Returns -1 in case of an error, 0 if tracing is disable or 1 if tracing
> + * is enabled.
> + */
> +int tracefs_trace_is_on(struct tracefs_instance *instance)
> +{
> + char buf[10];
> + int ret;
> + int fd;
> +
> + fd = tracefs_instance_file_open(instance, TRACE_CTRL, O_RDONLY);
> + if (fd < 0)
> + return -1;
> + ret = read(fd, buf, 10);
> + if (ret > 0) {
> + buf[9] = 0;
> + ret = atoi(buf);
> + } else {
> + ret = -1;
> + }
> + close(fd);
Wouldn't the above be better to use tracefs_instance_file_read_number()?
long long val;
ret = tracefs_instance_file_read_number(instance, TRACE_CTRL, &val);
if (ret < 0)
return -1;
return !!val;
-- Steve
> +
> + return ret;
> +}
> +
> +/**
> + * tracefs_trace_on - Enable writing traces to the ring buffer of the given instance
> + * @instance: ftrace instance, can be NULL for the top instance
> + *
> + * Returns -1 in case of an error or 0 otherwise
> + */
> +int tracefs_trace_on(struct tracefs_instance *instance)
> +{
> + return trace_on_off_file(instance, true);
> +}
> +
> +/**
> + * tracefs_trace_off - Disable writing traces to the ring buffer of the given instance
> + * @instance: ftrace instance, can be NULL for the top instance
> + *
> + * Returns -1 in case of an error or 0 otherwise
> + */
> +int tracefs_trace_off(struct tracefs_instance *instance)
> +{
> + return trace_on_off_file(instance, false);
> +}
> +
> +/**
> + * tracefs_trace_on_fd - Enable writing traces to the ring buffer
> + * @fd: File descriptor to ftrace tracing_on file, previously opened for reading
> + * with tracefs_instance_file_open()
> + *
> + * Returns -1 in case of an error or 0 otherwise
> + */
> +int tracefs_trace_on_fd(int fd)
> +{
> + if (fd < 0)
> + return -1;
> + return trace_on_off(fd, true);
> +}
> +
> +/**
> + * tracefs_trace_off_fd - Disable writing traces to the ring buffer
> + * @fd: File descriptor to ftrace tracing_on file, previously opened for reading
> + * with tracefs_instance_file_open()
> + *
> + * Returns -1 in case of an error or 0 otherwise
> + */
> +int tracefs_trace_off_fd(int fd)
> +{
> + if (fd < 0)
> + return -1;
> + return trace_on_off(fd, false);
> +}
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