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SubjectRe: [PATCH v2] [RFC] tracepoint: Add signal coredump tracepoint
Date
> KOSAKI Motohiro wrote:
> > 2009/12/3 Masami Hiramatsu<mhiramat@redhat.com>:
> >> Add signal coredump tracepoint which shows signal number,
> >> mm->flags, limits, pointer to file structure and core
> >> file name.
> >>
> >> This tracepoint requirement comes mainly from the viewpoint of
> >> administrators. Since now we have introduced many coredump
> >> configurations (e.g. dumpable, coredump_filter, core_pattern,
> >> etc) and some of them can be modified by users, it will be hard
> >> to know what was actually dumped (or not dumped) after some
> >> problem happened on the system. For example, a process didn't
> >> generated core, coredump doesn't have some sections, etc.
> >> In those cases, the coredump tracepoint can help us to know
> >> why the core file is so big or small, or not generated, by
> >> recording all configurations for all processes on the system.
> >> That will reduce system-administration cost.
> >
> > AFAIK, not-dumped case is important than dump successful case.
> > IOW, admin need to know why the crashed process was not dumped.
>
> Certainly, failure cases are important, but also, the cases
> that dumped-core doesn't or does include some sections
> are also important.

correct.

> > This tracepoint doesn't cover all failure case. especially
> > binfmt->core_dump() et.al.
> > IOW, this tracepoint seems too specialized piped-coredump feature.
>
> Hmm, so would you mean that after calling binfmt->core_dump()
> is better place?

I think your following use-case desired so. if you have unwritten reason, please correct me.

For example, a process didn't generated core, coredump doesn't have
some sections, etc.


> > What do you think this tracepoint's use case?
>
> Frankly to say, our first attempt was tracing mm->flags because
> it can be changed by users without asking, and they sometimes
> ask why core is not perfect or why core file is so big.
>
> Perhaps, covering all of those failure cases and succeed cases,
> gives better information for them. In that case, we might better
> tweak execution(goto) path to leave some error code on retval.

This is enough acceptable to me.

>
> e.g.
> if (IS_ERR(file))
> goto fail_dropcount;
> + retval = -EBADF;
> inode = file->f_path.dentry->d_inode;
> if (inode->i_nlink > 1)
> goto close_fail; /* multiple links - don't dump */
> if (!ispipe && d_unhashed(file->f_path.dentry))
> goto close_fail;
>
> /* AK: actually i see no reason to not allow this for named pipes etc.,
> but keep the previous behaviour for now. */
> if (!ispipe && !S_ISREG(inode->i_mode))
> goto close_fail;
> /*
> * Dont allow local users get cute and trick others to coredump
> * into their pre-created files:
> */
> + retval = -EPERM;
> if (inode->i_uid != current_fsuid())
> goto close_fail;
> + retval = -EINVAL;
> if (!file->f_op)
> goto close_fail;
> if (!file->f_op->write)
> goto close_fail;
> + retval = -EEXIST;
> if (!ispipe && do_truncate(file->f_path.dentry, 0, 0, file) != 0)
> goto close_fail;
>
>
> Thank you,
>
> --
> Masami Hiramatsu
>
> Software Engineer
> Hitachi Computer Products (America), Inc.
> Software Solutions Division
>
> e-mail: mhiramat@redhat.com
>





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