Re: [PATCH v7 0/5] printk: Userspace format indexing support

[Jessica Yu]

+++ Petr Mladek [17/06/21 12:10 +0200]:
> On Tue 2021-06-15 17:52:20, Chris Down wrote:
> > We have a number of systems industry-wide that have a subset of their
> > functionality that works as follows:
> >
> > 1. Receive a message from local kmsg, serial console, or netconsole;
> > 2. Apply a set of rules to classify the message;
> > 3. Do something based on this classification (like scheduling a
> >    remediation for the machine), rinse, and repeat.
> >
> > This provides a solution to the issue of silently changed or deleted
> > printks: we record pointers to all printk format strings known at
> > compile time into a new .printk_index section, both in vmlinux and
> > modules. At runtime, this can then be iterated by looking at
> > <debugfs>/printk/index/<module>, which emits the following format, both
> > readable by humans and able to be parsed by machines:
> >
> >     $ head -1 vmlinux; shuf -n 5 vmlinux
> >     # <level[,flags]> filename:line function "format"
> >     <5> block/blk-settings.c:661 disk_stack_limits "%s: Warning: Device %s is misaligned\n"
> >     <4> kernel/trace/trace.c:8296 trace_create_file "Could not create tracefs '%s' entry\n"
> >     <6> arch/x86/kernel/hpet.c:144 _hpet_print_config "hpet: %s(%d):\n"
> >     <6> init/do_mounts.c:605 prepare_namespace "Waiting for root device %s...\n"
> >     <6> drivers/acpi/osl.c:1410 acpi_no_auto_serialize_setup "ACPI: auto-serialization disabled\n"
> >
> > This mitigates the majority of cases where we have a highly-specific
> > printk which we want to match on, as we can now enumerate and check
> > whether the format changed or the printk callsite disappeared entirely
> > in userspace. This allows us to catch changes to printks we monitor
> > earlier and decide what to do about it before it becomes problematic.
> >
> > There is no additional runtime cost for printk callers or printk itself,
> > and the assembly generated is exactly the same.
> >
> > Chris Down (5):
> >   string_helpers: Escape double quotes in escape_special
> >   printk: Straighten out log_flags into printk_info_flags
> >   printk: Rework parse_prefix into printk_parse_prefix
> >   printk: Userspace format indexing support
> >   printk: index: Add indexing support to dev_printk
>
> The patchset looks ready for linux-next from my POV. I could fixup the
> messages as suggested by Andy when pushing.
>
> Well, I would still like to get acks from:
>
>   + Andy for the 1st patch
>   + Jessica for the changes in the module loader code in 4th patch.

Hi Petr, the module.{c,h} changes are fine by me:

    Acked-by: Jessica Yu <jeyu@xxxxxxxxxx>

Thank you,

Jessica