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SubjectRe: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm
On Mon, Jul 20, 2009 at 09:11:34PM -0400, Steven Rostedt wrote:
>
> On Thu, 16 Jul 2009, Jiri Olsa wrote:
>
> > If user setup set_ftrace_filter/set_ftrace_notrace files and then opens them
> > with read&write permissions, the previous setup will be removed.
>
> This is exactly what it was suppose to do.
>
> man fopen:
>
> w+ Open for reading and writing. The file is created if it does
> not exist, otherwise it is truncated. The stream is positioned
> at the beginning of the file.
>
> Which means that if you open a file for "w+" it will truncate it. Hence,
> you will remove all previous settings.
>
> What you want is:
>
> a+ Open for reading and appending (writing at end of file). The
> file is created if it does not exist. The initial file position
> for reading is at the beginning of the file, but output is
> always appended to the end of the file.
>
> Change the belowe code from "w+" to "a+" and you get your expected result.

My point was that if you open set_ftrace_filter/set_ftrace_notrace with just O_RDWR
perm. and will use the file just for reading, the filter will reset.

You're right about the "w+", there's the O_CREAT|O_TRUNC, sry I missed that.. ;)
Anyway with "r+" you'll get O_RDWR perm. only, showing the issue:

sh-4.0# echo "sys_open sys_write" > ./set_ftrace_filter
sh-4.0# cat ./set_ftrace_filter
sys_open
sys_write
sh-4.0# /ft ./set_ftrace_filter r+
#### all functions enabled ####
sh-4.0# cat ./set_ftrace_filter
#### all functions enabled ####
sh-4.0#

wbr,
jirka

>
> Thus, the current code is correct.
>
> -- Steve
>
>
>
> >
> > Tested with following program:
> >
> > [snip]
> > #include <stdio.h>
> > #include <string.h>
> >
> > int main(int argc, char **argv)
> > {
> > FILE *f;
> > char *mode = "w+";
> > char *file = argv[1];
> >
> > if (argc == 3)
> > mode = argv[2];
> >
> > if (NULL == (f = fopen(file, mode))) {
> > perror("fopen failed");
> > return -1;
> > }
> >
> > while(!feof(f)) {
> > #define BUFLEN 100
> > char buf[BUFLEN];
> > memset(buf, 0, BUFLEN);
> > fgets(buf, BUFLEN, f);
> > printf(buf);
> > }
> >
> > fclose(f);
> > return 0;
> > }
> > [snip]
> >
> > wbr,
> > jirka
> >
> >
> > Signed-off-by: Jiri Olsa <jolsa@redhat.com>
> >
> > ---
> > diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> > index 4521c77..11394bc 100644
> > --- a/kernel/trace/ftrace.c
> > +++ b/kernel/trace/ftrace.c
> > @@ -1661,10 +1661,6 @@ ftrace_regex_open(struct inode *inode, struct file *file, int enable)
> > return -ENOMEM;
> >
> > mutex_lock(&ftrace_regex_lock);
> > - if ((file->f_mode & FMODE_WRITE) &&
> > - !(file->f_flags & O_APPEND))
> > - ftrace_filter_reset(enable);
> > -
> > if (file->f_mode & FMODE_READ) {
> > iter->pg = ftrace_pages_start;
> > iter->flags = enable ? FTRACE_ITER_FILTER :
> > @@ -2260,6 +2256,9 @@ ftrace_regex_write(struct file *file, const char __user *ubuf,
> > return 0;
> >
> > mutex_lock(&ftrace_regex_lock);
> > + if ((file->f_mode & FMODE_WRITE) &&
> > + !(file->f_flags & O_APPEND))
> > + ftrace_filter_reset(enable);
> >
> > if (file->f_mode & FMODE_READ) {
> > struct seq_file *m = file->private_data;
> >


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