Merge branch 'net-sysctl-sentinel'

Merge branch 'net-sysctl-sentinel'

Joel Granados says:

====================
sysctl: Remove sentinel elements from networking

What?
These commits remove the sentinel element (last empty element) from the
sysctl arrays of all the files under the "net/" directory that register
a sysctl array. The merging of the preparation patches [4] to mainline
allows us to just remove sentinel elements without changing behavior.
This is safe because the sysctl registration code (register_sysctl() and
friends) use the array size in addition to checking for a sentinel [1].

Why?
By removing the sysctl sentinel elements we avoid kernel bloat as
ctl_table arrays get moved out of kernel/sysctl.c into their own
respective subsystems. This move was started long ago to avoid merge
conflicts; the sentinel removal bit came after Mathew Wilcox suggested
it to avoid bloating the kernel by one element as arrays moved out. This
patchset will reduce the overall build time size of the kernel and run
time memory bloat by about ~64 bytes per declared ctl_table array (more
info here [5]).

When are we done?
There are 4 patchest (25 commits [2]) that are still outstanding to
completely remove the sentinels: files under "net/" (this patchset),
files under "kernel/" dir, misc dirs (files under mm/ security/ and
others) and the final set that removes the unneeded check for ->procname
== NULL.

Testing:
* Ran sysctl selftests (./tools/testing/selftests/sysctl/sysctl.sh)
* Ran this through 0-day with no errors or warnings

Savings in vmlinux:
  A total of 64 bytes per sentinel is saved after removal; I measured in
  x86_64 to give an idea of the aggregated savings. The actual savings
  will depend on individual kernel configuration.
    * bloat-o-meter
        - The "yesall" config saves 3976 bytes (bloat-o-meter output [6])
        - A reduced config [3] saves 1263 bytes (bloat-o-meter output [7])

Savings in allocated memory:
  None in this set but will occur when the superfluous allocations are
  removed from proc_sysctl.c. I include it here for context. The
  estimated savings during boot for config [3] are 6272 bytes. See [8]
  for how to measure it.

Comments/feedback greatly appreciated

Changes in v6:
- Rebased onto net-next/main.
- Besides re-running my cocci scripts, I ran a new find script [9].
  Found 0 hits in net/
- Moved "i" variable declaraction out of for() in sysctl_core_net_init
- Removed forgotten sentinel in mpls_table
- Removed CONFIG_AX25_DAMA_SLAVE guard from net/ax25/ax25_ds_timer.c. It
  is not needed because that file is compiled only when
  CONFIG_AX25_DAMA_SLAVE is set.
- When traversing smc_table, stop on ARRAY_SIZE instead of ARRAY_SIZE-1.
- Link to v5: https://lore.kernel.org/r/20240426-jag-sysctl_remset_net-v5-0-e3b12f6111a6@samsung.com

Changes in v5:
- Added net files with additional variable to my test .config so the
  typo can be caught next time.
- Fixed typo tabel_size -> table_size
- Link to v4: https://lore.kernel.org/r/20240425-jag-sysctl_remset_net-v4-0-9e82f985777d@samsung.com

Changes in v4:
- Keep reverse xmas tree order when introducing new variables
- Use a table_size variable to keep the value of ARRAY_SIZE
- Separated the original "networking: Remove the now superfluous
  sentinel elements from ctl_table arra" into smaller commits to ease
  review
- Merged x.25 and ax.25 commits together.
- Removed any SOB from the commits that were changed
- Link to v3: https://lore.kernel.org/r/20240412-jag-sysctl_remset_net-v3-0-11187d13c211@samsung.com

Changes in v3:
- Reworkded ax.25
  - Added a BUILD_BUG_ON for the ax.25 commit
  - Added a CONFIG_AX25_DAMA_SLAVE guard where needed
- Link to v2: https://lore.kernel.org/r/20240328-jag-sysctl_remset_net-v2-0-52c9fad9a1af@samsung.com

Changes in v2:
- Rebased to v6.9-rc1
- Removed unneeded comment from sysctl_net_ax25.c
- Link to v1: https://lore.kernel.org/r/20240314-jag-sysctl_remset_net-v1-0-aa26b44d29d9@samsung.com
====================

Signed-off-by: David S. Miller <davem@davemloft.net>