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SubjectRe: [PATCH v4 14/15] livepatch: add /proc/<pid>/patch_state
On Tue, 31 Jan 2017, Josh Poimboeuf wrote:

> On Tue, Jan 31, 2017 at 03:31:39PM +0100, Miroslav Benes wrote:
> > On Thu, 19 Jan 2017, Josh Poimboeuf wrote:
> >
> > > Expose the per-task patch state value so users can determine which tasks
> > > are holding up completion of a patching operation.
> > >
> > > Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
> > > Reviewed-by: Petr Mladek <pmladek@suse.com>
> > > Reviewed-by: Miroslav Benes <mbenes@suse.cz>
> > > ---
> > > Documentation/filesystems/proc.txt | 18 ++++++++++++++++++
> > > fs/proc/base.c | 15 +++++++++++++++
> > > 2 files changed, 33 insertions(+)
> > >
> > > diff --git a/Documentation/filesystems/proc.txt b/Documentation/filesystems/proc.txt
> > > index 72624a1..85c501b 100644
> > > --- a/Documentation/filesystems/proc.txt
> > > +++ b/Documentation/filesystems/proc.txt
> > > @@ -44,6 +44,7 @@ Table of Contents
> > > 3.8 /proc/<pid>/fdinfo/<fd> - Information about opened file
> > > 3.9 /proc/<pid>/map_files - Information about memory mapped files
> > > 3.10 /proc/<pid>/timerslack_ns - Task timerslack value
> > > + 3.11 /proc/<pid>/patch_state - Livepatch patch operation state
> > >
> > > 4 Configuring procfs
> > > 4.1 Mount options
> > > @@ -1886,6 +1887,23 @@ Valid values are from 0 - ULLONG_MAX
> > > An application setting the value must have PTRACE_MODE_ATTACH_FSCREDS level
> > > permissions on the task specified to change its timerslack_ns value.
> > >
> > > +3.11 /proc/<pid>/patch_state - Livepatch patch operation state
> > > +-----------------------------------------------------------------
> > > +When CONFIG_LIVEPATCH is enabled, this file displays the value of the
> > > +patch state for the task.
> > > +
> > > +A value of '-1' indicates that no patch is in transition.
> > > +
> > > +A value of '0' indicates that a patch is in transition and the task is
> > > +unpatched. If the patch is being enabled, then the task hasn't been
> > > +patched yet. If the patch is being disabled, then the task has already
> > > +been unpatched.
> > > +
> > > +A value of '1' indicates that a patch is in transition and the task is
> > > +patched. If the patch is being enabled, then the task has already been
> > > +patched. If the patch is being disabled, then the task hasn't been
> > > +unpatched yet.
> > > +
> >
> > Despite my review I thought about this some more. I think the logic make
> > sense internally but when exposed it can be confusing. We do not export
> > klp_target_state value, so users have to know if a patch is being enabled
> > or disabled. Of course, they should know that, but I guess they'd like to
> > use an userspace tool for this. Such tool needs to look at
> > /proc/<pid>/patch_state to find out which tasks are blocking the
> > completion and that is it. No more information anywhere.
> >
> > We can either export klp_target_state, or change /proc/<pid>/patch_state
> > to show only two states - task is in transition (1), task is patched (0).
> >
> > What do you think?
>
> Isn't this information already available in
> /sys/kernel/livepatch/<patch>/{enabled,transition}?

transition no. That only gives the hint that something is happening with
the patch. But yes, enabled is the one I wanted. I don't know how I missed
that. Combined with /proc/<pid>/task it is exactly what a tool needs.

Miroslav

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