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Subject[PATCH v2 00/28] Printbufs (now with more printbufs!)
Date
So there's a lot of new stuff since the first posting:

- Printbufs have been broken up into multiple patches that each add distinct
functionality - this is intended to make it easier to review and to see
what's used for what

- Printbufs now support both auto-heap allocated buffers, and external/static
buffers: this was required for the vsprintf.c refactoring, and means they're
(almost) a direct replacement for seq_buf

- The big thing: a new %pf(%p) format string extension for calling pretty
printers from printf (idea from Matthew Wilcox)

This is intended to replace most of our other format string extensions: e.g.
instead of writing
printf("%pg", bdev);

You'd now write
printf("%pf(%p)", bdev_name, bdev);

The advantage of this is that pretty printers no longer have to live in
lib/vsprintf.c, and they're much more discoverable - you can cscope to the
pretty printer!

And my hope is that this will help induce people to write lots more pretty
printers; since they can now live with the code they're printing and don't
require touching code in vsprintf.c, there's less friction to creating new
ones.

We hope to standardize this extension as %(%p), but since gcc's printf format
checking doesn't yet understand that we're going with %pf(%p) for now.

Currently, we only support pointer arguments to pretty-printers. I think we
can improve this in the future to support at least integer arguments as well,
i.e. "%(%u)" will eventually work. This will require using libffi to do it
correctly, but it looks like libffi is nearly suitable for in kernel use (it
supports all linux architectures, and configured with the features we want it
compiles down to practically nothing).

- Massive vsprintf.c refactoring

printbufs are now the core data structure used by vsprintf.c - we're not
passing around a bunch of raw char pointers anymore! yay!

This gets us a sane standard calling convention for pretty printers - i.e.,
we need this for %pf(%p).

Couple notes on the refactoring:

- printf_spec has become a dumping ground of state, passed everywhere and
used inconsistently. The refactoring attempts to improve this, and
centralize printf_spec handling as much as possible near/in the top level
code that handles format strings. Some %p extensions use
field/width/precision in nonstandard ways; the refactoring patches make it
clearer where this is going on.

- a _lot_ of pretty printers were allocating secondary buffers on the stack,
mainly to avoid ever writing past the terminating null in the output
buffer. There was a test that checked for this, but it had no documentation
where the requirement came from nor does that requirement make any sense,
so I deleted it (if anyone knows anything about it, speak up!). The code
now takes the approach of just writing to the output buffer and then
truncating afterwards if required by the precision argument.

Yay, less stack usage!

- format string parsing is still a mess: I'd like to consolidate that to only
happen in one place, but that's going to be a much more involved
refactoring - and if we just switch to new-style calling pretty printers
directly, we'll be able to just delete all that code.

- More seq_buf conversions

Using printbufs to clean up vsprintf.c meant adding a second, non
heap-allocated mode, so printbufs now do almost everything seq_buf does -
seq_buf has a read_pos member for some reason (tracing?) that I didn't get
into.

So now seq_buf is just used by the tracing code, and that can also probably
be converted to printbuf, but seq_buf is Steven's thing so I'll let him take
a look before getting into that.

Kent Overstreet (28):
lib/printbuf: New data structure for printing strings
vsprintf: Convert to printbuf
vsprintf: %pf(%p)
lib/string_helpers: string_get_size() now returns characters wrote
lib/printbuf: Heap allocation
lib/printbuf: Tabstops, indenting
lib/printbuf: Unit specifiers
lib/pretty-printers: pr_string_option(), pr_bitflags()
vsprintf: Improve number()
vsprintf: pr_u64_minwidth(), pr_u64()
vsprintf: Lift pr_hex_bytes() out from hex_string()
test_printf: Drop requirement that sprintf not write past nul
vsprintf: Start consolidating printf_spec handling
vsprintf: Refactor resource_string()
vsprintf: Refactor fourcc_string()
vsprintf: Refactor ip_addr_string()
vsprintf: Refactor mac_address_string()
vsprintf: time_and_date() no longer takes printf_spec
vsprintf: flags_string() no longer takes printf_spec
vsprintf: Refactor device_node_string, fwnode_string
vsprintf: Refactor hex_string, bitmap_string_list, bitmap_string
Input/joystick/analog: Convert from seq_buf -> printbuf
mm/memcontrol.c: Convert to printbuf
clk: tegra: bpmp: Convert to printbuf
tools/testing/nvdimm: Convert to printbuf
powerpc: Convert to printbuf
x86/resctrl: Convert to printbuf
PCI/P2PDMA: Convert to printbuf

Documentation/core-api/printk-formats.rst | 19 +
arch/powerpc/kernel/process.c | 16 +-
arch/powerpc/kernel/security.c | 75 +-
arch/powerpc/platforms/pseries/papr_scm.c | 34 +-
arch/x86/kernel/cpu/resctrl/rdtgroup.c | 16 +-
drivers/clk/tegra/clk-bpmp.c | 21 +-
drivers/input/joystick/analog.c | 37 +-
drivers/pci/p2pdma.c | 17 +-
include/linux/kernel.h | 4 +
include/linux/pretty-printers.h | 11 +
include/linux/printbuf.h | 225 +++
include/linux/string_helpers.h | 8 +-
lib/Makefile | 2 +-
lib/pretty-printers.c | 81 ++
lib/printbuf.c | 252 ++++
lib/string_helpers.c | 18 +-
lib/test_printf.c | 23 +-
lib/vsprintf.c | 1612 ++++++++++-----------
mm/memcontrol.c | 68 +-
tools/testing/nvdimm/test/ndtest.c | 22 +-
20 files changed, 1527 insertions(+), 1034 deletions(-)
create mode 100644 include/linux/pretty-printers.h
create mode 100644 include/linux/printbuf.h
create mode 100644 lib/pretty-printers.c
create mode 100644 lib/printbuf.c

--
2.36.0

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