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    SubjectRe: [PATCH] tracer for sys_open() - sreadahead
    On Tue, Jan 27, 2009 at 11:43:03PM +0100, Frederic Weisbecker wrote:
    > On Tue, Jan 27, 2009 at 12:08:04PM -0800, Kok, Auke wrote:
    > >
    > > This tracer monitors regular file open() syscalls. This is a fast
    > > and low-overhead alternative to strace, and does not allow or
    > > require to be attached to every process.
    > >
    > > The tracer only logs succesfull calls, as those are the only ones we
    > > are currently interested in, and we can determine the absolute path
    > > of these files as we log.
    > >
    > > Signed-off-by: Auke Kok <auke-jan.h.kok@intel.com>
    >
    >
    > Hi Auke,
    >
    > Speaking about a global syscall tracer, I made a patch to trace only the syscalls
    > with the function-graph-tracer.
    >
    > http://lkml.org/lkml/2008/12/30/267
    >
    > Its approach and purpose is different than a tracer dedicated only to syscalls.
    > The function graph tracer traces execution graph of the functions and is more about
    > execution time spent and code flow whereas a syscall tracer can provide more specific
    > informations about syscalls.
    >
    > So both are not overlaping.
    >
    > But the low level part of my patch creates a thread flag _TIF_SYSCALL_TRACE which triggers

    s/_TIF_SYSCALL_TRACE/_TIF_SYSCALL_FTRACE

    _TIF_SYSCALL_TRACE is the one used by ptrace.


    > a ptrace hook when set.
    > This low-level part can easily be used by all tracers that would like to inspect syscalls.
    >
    > Just a change is needed: Steven requested that the part inside syscall_trace_enter become
    > a tracepoint, making it totally shareable between tracers and easy to turn on and off.
    >
    > And perhaps the parts that set/clear the flag on all tasks can be shared too.
    >
    > So we can start with this low-level syscall tracing facility. If you want, I can adapt
    > this low-level part and submit a patch this week or the next one to give you this base
    > infrastructure.
    >
    >
    > Once we have it, I think a syscall tracer can be fed with new syscalls events through
    > several patch iterations, starting with the open and close one :-)
    >
    > Are you ok with that?
    >
    > Steven, Ingo, do you agree?
    >
    >
    > >
    > > diff --git a/fs/open.c b/fs/open.c
    > > index a3a78ce..8cf2a6b 100644
    > > --- a/fs/open.c
    > > +++ b/fs/open.c
    > > @@ -30,6 +30,10 @@
    > > #include <linux/audit.h>
    > > #include <linux/falloc.h>
    > >
    > > +#include <trace/fs.h>
    > > +
    > > +DEFINE_TRACE(do_sys_open);
    > > +
    > > int vfs_statfs(struct dentry *dentry, struct kstatfs *buf)
    > > {
    > > int retval = -ENODEV;
    > > @@ -1040,6 +1044,7 @@ long do_sys_open(int dfd, const char __user *filename, int
    > > flags, int mode)
    > > fsnotify_open(f->f_path.dentry);
    > > fd_install(fd, f);
    > > }
    > > + trace_do_sys_open(f, flags, mode, fd);
    > > }
    > > putname(tmp);
    > > }
    > > diff --git a/include/trace/fs.h b/include/trace/fs.h
    > > new file mode 100644
    > > index 0000000..870eec2
    > > --- /dev/null
    > > +++ b/include/trace/fs.h
    > > @@ -0,0 +1,11 @@
    > > +#ifndef _TRACE_FS_H
    > > +#define _TRACE_FS_H
    > > +
    > > +#include <linux/fs.h>
    > > +#include <linux/tracepoint.h>
    > > +
    > > +DECLARE_TRACE(do_sys_open,
    > > + TPPROTO(struct file *filp, int flags, int mode, long fd),
    > > + TPARGS(filp, flags, mode, fd));
    > > +
    > > +#endif
    > > diff --git a/kernel/trace/Kconfig b/kernel/trace/Kconfig
    > > index e2a4ff6..0400815 100644
    > > --- a/kernel/trace/Kconfig
    > > +++ b/kernel/trace/Kconfig
    > > @@ -149,6 +149,15 @@ config CONTEXT_SWITCH_TRACER
    > > This tracer gets called from the context switch and records
    > > all switching of tasks.
    > >
    > > +config OPEN_CLOSE_TRACER
    > > + bool "Trace open() calls"
    > > + depends on DEBUG_KERNEL
    > > + select TRACING
    > > + select MARKERS
    > > + help
    > > + This tracer records open() syscalls. These calls are made when
    > > + files are accessed on disk.
    > > +
    > > config BOOT_TRACER
    > > bool "Trace boot initcalls"
    > > depends on DEBUG_KERNEL
    > > diff --git a/kernel/trace/Makefile b/kernel/trace/Makefile
    > > index 349d5a9..25cec6c 100644
    > > --- a/kernel/trace/Makefile
    > > +++ b/kernel/trace/Makefile
    > > @@ -20,6 +20,7 @@ obj-$(CONFIG_RING_BUFFER) += ring_buffer.o
    > >
    > > obj-$(CONFIG_TRACING) += trace.o
    > > obj-$(CONFIG_CONTEXT_SWITCH_TRACER) += trace_sched_switch.o
    > > +obj-$(CONFIG_OPEN_CLOSE_TRACER) += trace_open_close.o
    > > obj-$(CONFIG_SYSPROF_TRACER) += trace_sysprof.o
    > > obj-$(CONFIG_FUNCTION_TRACER) += trace_functions.o
    > > obj-$(CONFIG_IRQSOFF_TRACER) += trace_irqsoff.o
    > > diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
    > > index 4d3d381..24c17d2 100644
    > > --- a/kernel/trace/trace.h
    > > +++ b/kernel/trace/trace.h
    > > @@ -30,6 +30,7 @@ enum trace_type {
    > > TRACE_USER_STACK,
    > > TRACE_HW_BRANCHES,
    > > TRACE_POWER,
    > > + TRACE_OPEN,
    > >
    > > __TRACE_LAST_TYPE
    > > };
    > > diff --git a/kernel/trace/trace_open_close.c b/kernel/trace/trace_open_close.c
    > > new file mode 100644
    > > index 0000000..4250efc
    > > --- /dev/null
    > > +++ b/kernel/trace/trace_open_close.c
    > > @@ -0,0 +1,148 @@
    > > +/*
    > > + * trace open calls
    > > + * Copyright (C) 2009 Intel Corporation
    > > + *
    > > + * Based extensively on trace_sched_switch.c
    > > + * Copyright (C) 2007 Steven Rostedt <srostedt@redhat.com>
    > > + *
    > > + */
    > > +
    > > +#include <linux/module.h>
    > > +#include <linux/fs.h>
    > > +#include <linux/debugfs.h>
    > > +#include <linux/kallsyms.h>
    > > +#include <linux/uaccess.h>
    > > +#include <linux/ftrace.h>
    > > +#include <trace/fs.h>
    > > +
    > > +#include "trace.h"
    > > +
    > > +
    > > +static struct trace_array *ctx_trace;
    > > +static int __read_mostly open_trace_enabled;
    > > +static atomic_t open_ref;
    > > +
    > > +static void probe_do_sys_open(struct file *filp, int flags, int mode, long fd)
    > > +{
    > > + char *buf;
    > > + char *fname;
    > > +
    > > + if (!atomic_read(&open_ref))
    > > + return;
    > > +
    > > + if (!open_trace_enabled)
    > > + return;
    > > +
    > > + buf = kzalloc(PAGE_SIZE, GFP_KERNEL);
    > > + if (!buf)
    > > + return;
    > > + fname = d_path(&filp->f_path, buf, PAGE_SIZE);
    > > +
    > > + if (IS_ERR(fname))
    > > + goto out;
    > > +
    > > + ftrace_printk("%s: open(\"%s\", %d, %d) = %ld\n",
    > > + current->comm, fname, flags, mode, fd);
    > > +out:
    > > + kfree(buf);
    > > +}
    > > +
    > > +static void open_trace_reset(struct trace_array *tr)
    > > +{
    > > + tr->time_start = ftrace_now(tr->cpu);
    > > + tracing_reset_online_cpus(tr);
    > > +}
    > > +
    > > +static int open_trace_register(void)
    > > +{
    > > + int ret;
    > > +
    > > + ret = register_trace_do_sys_open(probe_do_sys_open);
    > > + if (ret) {
    > > + pr_info("open trace: Could not activate tracepoint"
    > > + " probe to do_open\n");
    > > + }
    > > +
    > > + return ret;
    > > +}
    > > +
    > > +static void open_trace_unregister(void)
    > > +{
    > > + unregister_trace_do_sys_open(probe_do_sys_open);
    > > +}
    > > +
    > > +static void open_trace_start(void)
    > > +{
    > > + long ref;
    > > +
    > > + ref = atomic_inc_return(&open_ref);
    > > + if (ref == 1)
    > > + open_trace_register();
    > > +}
    > > +
    > > +static void open_trace_stop(void)
    > > +{
    > > + long ref;
    > > +
    > > + ref = atomic_dec_and_test(&open_ref);
    > > + if (ref)
    > > + open_trace_unregister();
    > > +}
    > > +
    > > +void open_trace_start_cmdline_record(void)
    > > +{
    > > + open_trace_start();
    > > +}
    > > +
    > > +void open_trace_stop_cmdline_record(void)
    > > +{
    > > + open_trace_stop();
    > > +}
    > > +
    > > +static void open_start_trace(struct trace_array *tr)
    > > +{
    > > + open_trace_reset(tr);
    > > + open_trace_start_cmdline_record();
    > > + open_trace_enabled = 1;
    > > +}
    > > +
    > > +static void open_stop_trace(struct trace_array *tr)
    > > +{
    > > + open_trace_enabled = 0;
    > > + open_trace_stop_cmdline_record();
    > > +}
    > > +
    > > +static int open_trace_init(struct trace_array *tr)
    > > +{
    > > + ctx_trace = tr;
    > > +
    > > + open_start_trace(tr);
    > > + return 0;
    > > +}
    > > +
    > > +static void reset_open_trace(struct trace_array *tr)
    > > +{
    > > + open_stop_trace(tr);
    > > +}
    > > +
    > > +static struct tracer open_trace __read_mostly =
    > > +{
    > > + .name = "open",
    > > + .init = open_trace_init,
    > > + .reset = reset_open_trace,
    > > +};
    > > +
    > > +__init static int init_open_trace(void)
    > > +{
    > > + int ret = 0;
    > > +
    > > + if (atomic_read(&open_ref))
    > > + ret = open_trace_register();
    > > + if (ret) {
    > > + pr_info("error registering open trace\n");
    > > + return ret;
    > > + }
    > > + return register_tracer(&open_trace);
    > > +}
    > > +device_initcall(init_open_trace);
    > > +
    > > --
    > > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
    > > the body of a message to majordomo@vger.kernel.org
    > > More majordomo info at http://vger.kernel.org/majordomo-info.html
    > > Please read the FAQ at http://www.tux.org/lkml/



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