btrfs-progs: docs: update kernel coding style

[ci skip]

Signed-off-by: David Sterba <dsterba@suse.com>

Author: kdave

Documentation/dev/Development-notes.rst

@@ -224,6 +224,9 @@ attention to detail. Once written the code could stay unchanged for years but
 will be read many times. `Read more
 <https://simpleprogrammer.com/maintaining-code/>`__.
 
+General advice: *Try to keep the same style and formatting of the code that's
+already there.*
+
 Patches
 ^^^^^^^
 
@@ -277,6 +280,8 @@ Headers
 ^^^^^^^
 
 -  leave one newline before #endif in headers
+-  include headers that add usage of a data structure or API, also remove such
+   header with last use of the API
 
 Comments
 ^^^^^^^^
@@ -330,6 +335,9 @@ Misc
 -  fix spelling, grammar and formatting of comments that get moved or changed
 -  fix coding style in code that's only moved
 -  one newline between functions
+-  80 chars per line are recommended but longer lines are OK (up to 90) if the
+   code "looks better" without the line break, e.g. if half of the word is beyond 80 chars
+   but it's clear what it is, or function prototypes do not need to wrap arguments
 
 Locking
 ^^^^^^^
@@ -346,8 +354,20 @@ Code
 -  default function return value is *int ret*, temporary return values should
    be named like *ret2* etc
 -  structure initializers should use *{ 0 }*
--  do not use *short* type if possible, if it fits to char/u8 use it instead,
-   or plain int
+-  do not use *short int* type if possible, if it fits to char/u8 use it instead,
+   or plain int/u32
+-  memory barriers need to be always documented
+-  add *const* to parameters that are not modified
+-  use bool for indicators and bool status variables (not int)
+-  use matching int types (size, signedness), with exceptions
+-  use ENUM_BIT for enumerated bit values (that don't have assigned fixed numbers)
+-  add function annotations __cold, __init, __attribute_const__ if applicable
+-  use automatic variable cleanup for:
+   -  *struct btrfs_path* with BTRFS_PATH_AUTO_FREE
+-  use of ``unlikely()`` annotation is OK and recommended for the following cases:
+
+   -  control flow of the function is changed due to error handling and it
+      leads to *never-happens* errors like EUCLEAN, EIO
 
 Output
 ^^^^^^
@@ -368,7 +388,8 @@ Expressions, operators
    -  *a \* b + c*, *(a << b) + c*, *(a % b) + c*
 
 -  64bit division is not allowed, either avoid it completely, or use bit
-   shifts or use div_u64 helpers
+   shifts or use div_u64 helpers; do not use *do_div* for division as it's a
+   macro and has side effects
 -  do not use chained assignments: no *a = b = c;*
 
 Variable declarations, parameters
@@ -380,6 +401,8 @@ Variable declarations, parameters
 -  use *const* extensively
 -  add temporary variable to store a value if it's used multiple times in the
    function, or if reading the value needs to chase a long pointer chain
+-  do not mix declarations and statements (although kernel uses C standard that
+   allos that)
 
 Kernel config options
 ---------------------
@@ -449,9 +472,9 @@ Please refer to the option documentation for further details.
 BUG: MAX_LOCKDEP_CHAIN_HLOCKS too low!
 ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
 
-Not a bug. The lockdep structures can get in some cases full and cannot
-properly track locks anymore. There's only a workaround to increase the kernel
-config value of CONFIG_LOCKDEP_CHAINS_BITS, default is
+Not a bug and please don't report it. The lockdep structures can get in some
+cases full and cannot properly track locks anymore. There's only a workaround
+to increase the kernel config value of CONFIG_LOCKDEP_CHAINS_BITS, default is
 16, 18 tends to work, increase if needed.
 
 fstests setup
@@ -520,10 +543,11 @@ Note: This list may be incomplete.
 Storage environment
 ^^^^^^^^^^^^^^^^^^^
 
--  At least 4 identically sized partitions/disks/virtual disks, specified using
-   ``$SCRATCH_DEV_POOL``, some tests may require 8 such partitions
+-  at least 4 identically sized partitions/disks/virtual disks, specified using
+   ``$SCRATCH_DEV_POOL``
+-  some tests may require 8 equally sized``SCRATCH_DEV_POOL`` partitions
 -  some tests need at least 10G of free space, as determined by ``df``, i.e.
-   the size of the device may need to be larger
+   the size of the device may need to be larger, 12G should work
 -  some tests require ``$LOGWRITES_DEV``, yet another separate block device,
    for power fail testing
 -  for testing trim and discard, the devices must be capable of that (physical