From: Petr Mladek <pmladek@suse.com>
To: Kent Overstreet <kent.overstreet@gmail.com>
Cc: linux-kernel@vger.kernel.org, linux-mm@vger.kernel.org,
rostedt@goodmis.org, senozhatsky@chromium.org,
andriy.shevchenko@linux.intel.com, willy@infradead.org
Subject: Re: [PATCH v2 01/28] lib/printbuf: New data structure for printing strings
Date: Fri, 27 May 2022 12:29:20 +0200 [thread overview]
Message-ID: <YpCoADIEWi9flgSf@alley> (raw)
In-Reply-To: <20220526152127.gw7gb4jnoikop4hl@moria.home.lan>
On Thu 2022-05-26 11:21:27, Kent Overstreet wrote:
> On Thu, May 26, 2022 at 05:06:15PM +0200, Petr Mladek wrote:
> > On Thu 2022-05-19 13:23:54, Kent Overstreet wrote:
> > > This adds printbufs: a printbuf points to a char * buffer and knows the
> > > size of the output buffer as well as the current output position.
> > >
> > > Future patches will be adding more features to printbuf, but initially
> > > printbufs are targeted at refactoring and improving our existing code in
> > > lib/vsprintf.c - so this initial printbuf patch has the features
> > > required for that.
> >
> > > diff --git a/include/linux/printbuf.h b/include/linux/printbuf.h
> > > new file mode 100644
> > > index 0000000000..40dc07040d
> > > --- /dev/null
> > > +++ b/include/linux/printbuf.h
> > > +static inline void pr_chars(struct printbuf *out, char c, unsigned n)
> > > +{
> > > + memset(out->buf + out->pos,
> > > + c,
> > > + min(n, printbuf_remaining(out)));
> > > + out->pos += n;
> > > + printbuf_nul_terminate(out);
> > > +}
> >
> > This function is not later used. Please, do not add API
> > that will not have users in the same patchset.
> >
> > There are several other cases. I am not going to comment
> > all of them.
>
> It is used in this patchset, in lib/vsnprintf.c. You sure about the other cases?
Ah, I used outdated cscope. This was bad example.
> > > +static inline void __pr_char(struct printbuf *out, char c)
> > > +{
> > > + if (printbuf_remaining(out))
> > > + out->buf[out->pos] = c;
> > > + out->pos++;
> > > +}
> > > +
> > > +static inline void pr_char(struct printbuf *out, char c)
> > > +{
> > > + __pr_char(out, c);
> > > + printbuf_nul_terminate(out);
> > > +}
> >
> > The "pr_" prefix is a nightmare for me because the same prefix
> > is used also for printk() API ;-)
> >
> > Could we please use "pb_" instead?
>
> I'm not entirely against that, but I see printbufs as already in this patchset
> tightly coupled to vsprintf.c and thus quite related to printk, as well - and
> there aren't that many different pr_ things. So I think the shared prefix makes
> some sense, I'd like to hear what others think before making that change.
I would really like to keep the three APIs separated and easy to
distinguish. They are principally different:
1. pr_*() API:
+ wrapper to printk(). They makes the messages available on
console and for user-space log daemons while printf()
+ the various pr_*() variants are used to define kernel
specific features and behavior, for example:
loglevel, ratelimit, only once. deferred console handling.
+ uses implicit (system) buffer
+ The message format is defined by the 1st parameter. It
is the same way as printf() in user-space.
+ It is inspired by printf() from user-space that prints
the messages to the standard output.
2. *s*printf() APIs:
+ basically duplicate the same user-space API. It supports
some extra %p modifiers. There might be few more
incompatibilities.
+ use simple "char *" buffer provided as the 1st parameter
+ the messages format is defined the same way as in
the user-space counterparts.
3. printbuf API:
+ append messages into the given printbuf by small pieces
+ format defined by the suffix, for example, _char(),
bytes(), units_64(), _tab(), indent()
+ allows to do special operations on the buffer,
for example, _reset(), make_room(), atomic_inc()
+ it will be used as low-level API for vscnprinf()
implementation, pretty printing API, or
stand alone uses.
+ I wonder if there will be variant that will allow
to pass the format in the printf() way, e.g.
int pb_printf(printbuf *buf, const char *fmt, ...);
+ is there any user space counter part?
Now, it is clear that printfbuf API must be distinguished by another
prefix:
+ it must be clear that it stores the output into printbuf.
It is similar to dprintf(), fprintf(), sprintf().
+ It can't be done by the suffix because it is already used
to define format of the appended string or extra operation.
+ It must be clear what is low-level API used to implement
vsprintf() and high-level API that uses vsprintf().
I mean pb_char() vs. pb_printf().
Best Regards,
Petr
PS: I probably won't find time to write more comments on this patchset
today. I'll continue the following week. It seems that it will
be a long journey.
next prev parent reply other threads:[~2022-05-27 10:29 UTC|newest]
Thread overview: 62+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-19 17:23 [PATCH v2 00/28] Printbufs (now with more printbufs!) Kent Overstreet
2022-05-19 17:23 ` [PATCH v2 01/28] lib/printbuf: New data structure for printing strings Kent Overstreet
2022-05-19 18:21 ` Matthew Wilcox
2022-05-20 4:44 ` Kent Overstreet
2022-05-26 15:06 ` Petr Mladek
2022-05-26 15:21 ` Kent Overstreet
2022-05-26 15:36 ` Joe Perches
2022-05-27 10:29 ` Petr Mladek [this message]
2022-05-29 18:15 ` Kent Overstreet
2022-05-31 22:03 ` Kent Overstreet
2022-05-19 17:23 ` [PATCH v2 02/28] vsprintf: Convert to printbuf Kent Overstreet
2022-05-19 17:23 ` [PATCH v2 03/28] vsprintf: %pf(%p) Kent Overstreet
2022-05-19 18:33 ` Matthew Wilcox
2022-05-20 4:43 ` Kent Overstreet
2022-05-19 21:06 ` David Laight
2022-05-19 21:15 ` Matthew Wilcox
2022-05-20 8:03 ` David Laight
2022-05-20 13:08 ` Matthew Wilcox
2022-05-20 4:49 ` Kent Overstreet
2022-05-20 14:17 ` andriy.shevchenko
2022-05-19 21:20 ` Matthew Wilcox
2022-05-20 7:40 ` Michal Hocko
2022-05-20 15:01 ` Kent Overstreet
2022-05-20 17:56 ` Kent Overstreet
2022-05-19 17:23 ` [PATCH v2 04/28] lib/string_helpers: string_get_size() now returns characters wrote Kent Overstreet
2022-05-19 17:23 ` [PATCH v2 05/28] lib/printbuf: Heap allocation Kent Overstreet
2022-05-19 17:23 ` [PATCH v2 06/28] lib/printbuf: Tabstops, indenting Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 07/28] lib/printbuf: Unit specifiers Kent Overstreet
2022-05-19 20:21 ` Andy Shevchenko
2022-05-19 20:26 ` Kent Overstreet
2022-05-19 21:11 ` Matthew Wilcox
2022-05-20 4:40 ` Kent Overstreet
2022-05-19 21:16 ` Andy Shevchenko
2022-05-19 21:22 ` Matthew Wilcox
2022-05-20 4:36 ` Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 08/28] lib/pretty-printers: pr_string_option(), pr_bitflags() Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 09/28] vsprintf: Improve number() Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 10/28] vsprintf: pr_u64_minwidth(), pr_u64() Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 11/28] vsprintf: Lift pr_hex_bytes() out from hex_string() Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 12/28] test_printf: Drop requirement that sprintf not write past nul Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 13/28] vsprintf: Start consolidating printf_spec handling Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 14/28] vsprintf: Refactor resource_string() Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 15/28] vsprintf: Refactor fourcc_string() Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 16/28] vsprintf: Refactor ip_addr_string() Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 17/28] vsprintf: Refactor mac_address_string() Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 18/28] vsprintf: time_and_date() no longer takes printf_spec Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 19/28] vsprintf: flags_string() " Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 20/28] vsprintf: Refactor device_node_string, fwnode_string Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 21/28] vsprintf: Refactor hex_string, bitmap_string_list, bitmap_string Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 22/28] Input/joystick/analog: Convert from seq_buf -> printbuf Kent Overstreet
2022-05-19 20:04 ` Andy Shevchenko
2022-05-19 20:19 ` Kent Overstreet
2022-05-19 21:09 ` Andy Shevchenko
2022-05-19 17:24 ` [PATCH v2 23/28] mm/memcontrol.c: Convert to printbuf Kent Overstreet
2022-05-20 7:59 ` Michal Hocko
2022-05-19 17:24 ` [PATCH v2 24/28] clk: tegra: bpmp: " Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 25/28] tools/testing/nvdimm: " Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 26/28] powerpc: " Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 27/28] x86/resctrl: " Kent Overstreet
2022-05-19 17:24 ` [PATCH v2 28/28] PCI/P2PDMA: " Kent Overstreet
2022-05-26 14:44 ` [PATCH v2 00/28] Printbufs (now with more printbufs!) Petr Mladek
2022-05-26 15:11 ` Kent Overstreet
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