From: Kent Overstreet > Sent: 20 June 2022 01:42 > > Previous discussions: > https://lore.kernel.org/all/20220419203202.2670193-1-kent.overstreet@xxxxxxxxx/ > https://lore.kernel.org/all/20220519172421.162394-1-kent.overstreet@xxxxxxxxx/ > https://lore.kernel.org/all/20220604193042.1674951-1-kent.overstreet@xxxxxxxxx/ > > Git repo: > https://evilpiepirate.org/git/bcachefs.git/log/?h=printbuf_v4 > > Changes since v3: > Bugfixes and performance improvements, the latest iteration of this patch > series has been baking in the bcachefs tree and that shook out some bugs. > > Rasmus pointed out that -fno-strict-aliasing is going to cause gcc to generate > nasty code, and indeed it unfortunately does but according to worst case > scenario microbenchmarks it's not a problem for actual performance. Just copy some of the structure members to local variables and, if necessary, write them back at the end. > Using > memcpy() and memset() in the printbuf helpers _was_ a problem for performance, > so that's been fixed. > > ----------- > > Core idea: Wouldn't it be nice if we had a common data structure and calling > convention for outputting strings? > > The core concept this patch series is aimed at cleaning up and standardizing is > that of a "pretty-printer", which is now a function like prt_foo() or > foo_to_text(): > > void foo_to_text(struct printbuf *out, struct foo) > > What this patch series does or enables: > > - It becomes quite a bit easier to write composable pretty printers! This is > huge. > > - A ton of code that works in terms of raw char * pointers and lengths > (snprintf style, and many weird variations) gets cleaned up, with error prone > raw pointers arithmetic replaced by proper helpers > > - A ton of code that emits either directly via printk() or to other places > (sysfs, debugfs) can now output to printbufs, and becomes more reusable and > composable > > - Countesy of Matthew Wilcox, the new and very cool %pf() format string, which > allows passing a pretty printer function and its arguments to sprintf() and > family. This means we can now call type specific pretty-printers without > adding them to lib/vsprintf.c and writing a bunch of crazy > parsing-and-dispatch code. For example, > > printk("%pd", dentry); > > becomes > > printk("%pf(%p)", prt_dentry, dentry); > > My OOM debugging & reporting patch series that builds off of this uses this > to solve a very real problem that Michal Hocko brought up at LSF - with this > we write shrinkers_to_text(), slab_to_text() which can _also_ now be used for > reporting in debugfs (which Roman has been working on), as well as in the > show_mem() report - the "%pf()" syntax lets us print the output of those > functions without allocating (and having to preallocate) a separate buffer. I really think that is a bad idea. printk() already uses a lot of stack, anything doing a recursive call is just making that worse. Especially since these calls can often be in error paths which are not often tested and can already be on deep stacks. David > > - Some new formatting helpers: > > Nicely aligned text is much easier to read, and something that we want a > _lot, but outputting nicely aligned text with printf() is a pain in the ass. > Printbufs add tabstops, which can be used for right or left justification - > simple, easy. prt_tab() emits spaces up to the next tabstop, prt_tab_rjust() > advances to the next tabstop right justifying text since the previous > tabstop. > > Printbufs also add an indent level, obeyed by prt_newline() which can be very > useful for multi line output. > > In the future, \n and \t in format strings may learn to obey these as well. > > - Optional heap allocation - no need to statically allocate buffers on the > stack and guess at the output size. > > - Lots of consolidating and refactoring > > This series replaces seq_buf, which does basically what an earlier version of > printbufs did. > > A good chunk of lib/string_helpers.c, as well as lib/hexdump.c are converted > (and simplified!). > > Pretty printers in lib/vsprintf.c previously outputted to buffers on the > stack and then copied _that_ to the actual output buffer, that's all gone > (replaced by proper helpers for outputting chars and strings), and they also > used printf_spec for argument passing in ad-hoc ways. This patch series does > a lot towards converting them to more standard pretty printers that can be > called via %pf() instead of having to live in lib/vsprintf.c. Still to do: > format string decoding for argument passing is a mess that's scattered all > over the place. > > In the course of working on this patch series, I've spotted a _lot_ more > consolidation and refactoring that needs to be done - we've got a ton of API > fragmentation leading to lots of code duplication. > > But I'm already really excited about what this patch series enables. > > Cheers! > > Kent Overstreet (34): > lib/printbuf: New data structure for printing strings > lib/string_helpers: Convert string_escape_mem() to printbuf > vsprintf: Convert to printbuf > lib/hexdump: 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: prt_string_option(), prt_bitflags() > vsprintf: Improve number() > vsprintf: prt_u64_minwidth(), prt_u64() > 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 > tracing: trace_events_synth: Convert to printbuf > d_path: prt_path() > ACPI/APEI: Add missing include > tracing: Convert to printbuf > Delete seq_buf > > Documentation/core-api/printk-formats.rst | 22 + > 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/acpi/apei/erst-dbg.c | 1 + > drivers/clk/tegra/clk-bpmp.c | 21 +- > drivers/input/joystick/analog.c | 23 +- > drivers/pci/p2pdma.c | 21 +- > fs/d_path.c | 35 + > include/linux/dcache.h | 1 + > include/linux/kernel.h | 12 + > include/linux/pretty-printers.h | 10 + > include/linux/printbuf.h | 253 +++ > include/linux/seq_buf.h | 162 -- > include/linux/string.h | 5 + > include/linux/string_helpers.h | 8 +- > include/linux/trace_events.h | 2 +- > include/linux/trace_seq.h | 17 +- > kernel/trace/trace.c | 45 +- > kernel/trace/trace_dynevent.c | 34 +- > kernel/trace/trace_events_filter.c | 2 +- > kernel/trace/trace_events_synth.c | 32 +- > kernel/trace/trace_functions_graph.c | 6 +- > kernel/trace/trace_kprobe.c | 2 +- > kernel/trace/trace_seq.c | 111 +- > lib/Makefile | 4 +- > lib/hexdump.c | 246 +-- > lib/pretty-printers.c | 60 + > lib/printbuf.c | 253 +++ > lib/seq_buf.c | 397 ----- > lib/string_helpers.c | 224 +-- > lib/test_hexdump.c | 30 +- > lib/test_printf.c | 33 +- > lib/vsprintf.c | 1723 ++++++++++----------- > mm/memcontrol.c | 68 +- > tools/testing/nvdimm/test/ndtest.c | 22 +- > 37 files changed, 2050 insertions(+), 1976 deletions(-) > create mode 100644 include/linux/pretty-printers.h > create mode 100644 include/linux/printbuf.h > delete mode 100644 include/linux/seq_buf.h > create mode 100644 lib/pretty-printers.c > create mode 100644 lib/printbuf.c > delete mode 100644 lib/seq_buf.c > > -- > 2.36.1 - Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK Registration No: 1397386 (Wales)
