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SubjectRe: [PATCH] tracing: dont reset set_ftrace_filter/notrace when opened with r/w perm

On Wed, 22 Jul 2009, Jiri Olsa wrote:

> 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:

Ah, then the fix would be to check against O_TRUNC.

-- Steve


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