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    SubjectRe: [PATCH] tracer for sys_open() - sreadahead
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    2009/1/28 Ananth N Mavinakayanahalli <ananth@in.ibm.com>:
    > On Wed, Jan 28, 2009 at 03:21:24PM +0100, Frédéric Weisbecker wrote:
    >> 2009/1/28 Ananth N Mavinakayanahalli <ananth@in.ibm.com>:
    >> > On Tue, Jan 27, 2009 at 11:43:05PM +0100, Frederic Weisbecker wrote:
    >> >> On Tue, Jan 27, 2009 at 12:08:04PM -0800, Kok, Auke wrote:
    >
    > ...
    >
    >> > Here is something I did sometime ago that uses utrace. It is per task
    >> > doesn't use ftrace and is just intended as a prototype. It traces both
    >> > syscalls and returns.
    >> >
    >> > ---
    >> >
    >> > Here is the beginnings of a simple utrace based strace. Right now, one
    >> > needs to invoke this program with a 'insmod <modname> tid=<tid>'.
    >> >
    >> > The output looks something like this:
    >> > [267352.641112] Attached to 32604 => 0xd8f60090
    >> > [267353.981046] 2
    >> > [267353.981085] 197 0x1 0xbff8cd84 0x86cff4 0x86d4c0 0x86d4c0 0xbff8cd50a = 0
    >> > [267353.981097] 192 0x0 0x1000 0x3 0x22 0xffffffff 0x0 = b7f8d000
    >> > [267353.981124] 4 0x1 0xb7f8d000 0xd 0xd 0xb7f8d000 0xbff8cda8 = d
    >> > [267353.981174] 4 0x1 0xb7f8d000 0x3 0x3 0xb7f8d000 0xbff8c7dc = 3
    >> > [267353.981209] 252 0x0 0x0 0x86e0d0 0x0 0x86b274 0xbff8cee8 =
    >> > [267353.981215] Task 32604 exited
    >> > [267355.460180] Cannot find PID 32604
    >> >
    >> > I know strace does a pretty print, but this is a quick and dirty
    >> > prototype.
    >> > ---
    >> >
    >> > #include <linux/module.h>
    >> > #include <linux/utrace.h>
    >> > #include <linux/err.h>
    >> > #include <asm/syscall.h>
    >> >
    >> > MODULE_DESCRIPTION("syscall trace");
    >> > MODULE_LICENSE("GPL");
    >> >
    >> > static int target_tid;
    >> >
    >> > module_param_named(tid, target_tid, int, 0);
    >> >
    >> > static u32 task_syscall_entry(u32 action, struct utrace_attached_engine *engine,
    >> > struct task_struct *task, struct pt_regs *regs)
    >> > {
    >> > long callno;
    >> > unsigned long args[6];
    >> >
    >> > callno = syscall_get_nr(task, regs);
    >> > syscall_get_arguments(task, regs, 0, 6, args);
    >> >
    >> > printk(KERN_INFO "%ld 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx 0x%lx = ",
    >> > callno, args[0], args[1], args[2], args[3], args[4], args[5]);
    >> > return UTRACE_RESUME;
    >> > }
    >> >
    >> > static u32 task_syscall_exit(u32 action, struct utrace_attached_engine *engine,
    >> > struct task_struct *task, struct pt_regs *regs)
    >> > {
    >> > long retval = syscall_get_return_value(task, regs);
    >> > printk("%lx\n", retval);
    >> > return UTRACE_RESUME;
    >> > }
    >> >
    >> > static u32 task_exit(enum utrace_resume_action action,
    >> > struct utrace_attached_engine *engine, struct task_struct *task,
    >> > long orig_code, long *code)
    >> > {
    >> > printk("\n");
    >> > printk(KERN_INFO "Task %d exited\n", target_tid);
    >> > return UTRACE_DETACH;
    >> > }
    >> >
    >> > static const struct utrace_engine_ops syscall_ops =
    >> > {
    >> > .report_syscall_entry = task_syscall_entry,
    >> > .report_syscall_exit = task_syscall_exit,
    >> > .report_exit = task_exit,
    >> > };
    >> >
    >> > static int __init strace_init(void)
    >> > {
    >> > struct pid *pid;
    >> > int ret = 0;
    >> > struct task_struct *target;
    >> > struct utrace_attached_engine *engine;
    >> >
    >> > pid = find_get_pid(target_tid);
    >> > if (pid == NULL) {
    >> > printk(KERN_ERR "Cannot find PID %d\n", target_tid);
    >> > ret = -ESRCH;
    >> > goto out;
    >> > }
    >> >
    >> > engine = utrace_attach_pid(pid, UTRACE_ATTACH_CREATE, &syscall_ops, 0);
    >> > if (IS_ERR(engine)) {
    >> > printk(KERN_ERR "utrace_attach_pid: %ld\n", PTR_ERR(engine));
    >> > ret = -EINVAL;
    >> > goto out;
    >> > } else if (engine == NULL) {
    >> > printk(KERN_ERR "utrace_attach_pid => NULL\n");
    >> > ret = -EINVAL;
    >> > goto out;
    >> > } else
    >> > printk(KERN_INFO "Attached to %d => 0x%p\n",
    >> > target_tid, engine);
    >> >
    >> > /*
    >> > * If utrace_attach_pid() succeeded above, we are sure the target
    >> > * is valid here
    >> > */
    >> > target = pid_task(pid, PIDTYPE_PID);
    >> > put_pid(pid);
    >> >
    >> > ret = utrace_set_events(target, engine, UTRACE_EVENT_SYSCALL |
    >> > UTRACE_EVENT(EXIT));
    >> > if (ret)
    >> > printk(KERN_ERR "utrace_set_events returned %d\n", ret);
    >> >
    >> > out:
    >> > return ret;
    >> > }
    >> >
    >> > static void __exit strace_exit(void)
    >> > {
    >> > int ret = 0;
    >> > struct pid *pid;
    >> > struct utrace_attached_engine *engine;
    >> > struct task_struct *target;
    >> >
    >> > pid = find_get_pid(target_tid);
    >> > if (pid == NULL) {
    >> > printk(KERN_ERR "Cannot find PID %d\n", target_tid);
    >> > return;
    >> > }
    >> >
    >> > target = pid_task(pid, PIDTYPE_PID);
    >> > put_pid(pid);
    >> > engine = utrace_attach_task(target, UTRACE_ATTACH_MATCH_OPS,
    >> > &syscall_ops, 0);
    >> > if (IS_ERR(engine))
    >> > printk(KERN_ERR "Can't find self: %ld\n", PTR_ERR(engine));
    >> > else if (engine == NULL)
    >> > printk(KERN_ERR "Can't find self: no match\n");
    >> > else {
    >> > printk(KERN_INFO "Trying detach 0x%p from %d\n",
    >> > engine, target_tid);
    >> > ret = utrace_control(target, engine, UTRACE_DETACH);
    >> > if (ret)
    >> > printk(KERN_ERR "utrace_control returned %d\n",
    >> > ret);
    >> > }
    >> > }
    >> >
    >> > module_init(strace_init);
    >> > module_exit(strace_exit);
    >> >
    >>
    >>
    >> This is a very convenient Api. I would be glad to use it with ftrace.
    >> But, what is it's status currently? Some projects to merge it?
    >
    > Its currently available as a git tree:
    > git://git.kernel.org/pub/scm/linux/kernel/git/frob/linux-2.6-utrace.git
    >
    > There is work going on to merge it upstream. Roland McGrath will be able
    > to better answer when. However, one of the biggest requirements to merge
    > it is an in-kernel user. Hopefully Frank's prototype and/or an ftrace
    > integration of the above snippet should be incentive to push for some
    > in-tree users :-)
    >
    > Ananth
    >

    I hope so. That would be used by the function graph tracer and a
    syscall tracer, and probably for other special tracers
    needs. If Ingo and Steven are ok with it.
    --
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