Docs: Move magic-number from process to staging

'Other material' section on 'process/index' is for unsorted documents.
However we also have a dedicated place for the purpose, 'staging/'.
Move 'magic-number' from the section to 'staging/' directory.

Signed-off-by: SeongJae Park <sj@kernel.org>
Acked-by: Federico Vaga <federico.vaga@vaga.pv.it>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Link: https://lore.kernel.org/r/20240624185312.94537-4-sj@kernel.org

Documentation/process/index.rst

@@ -113,7 +113,6 @@ lack of a better place.
 .. toctree::
    :maxdepth: 1
 
-   magic-number
    clang-format
 
 .. only::  subproject and html

Documentation/process/magic-number.rst

@@ -1,84 +0,0 @@
-.. _magicnumbers:
-
-Linux magic numbers
-===================
-
-This file is a registry of magic numbers which are in use.  When you
-add a magic number to a structure, you should also add it to this
-file, since it is best if the magic numbers used by various structures
-are unique.
-
-It is a **very** good idea to protect kernel data structures with magic
-numbers.  This allows you to check at run time whether (a) a structure
-has been clobbered, or (b) you've passed the wrong structure to a
-routine.  This last is especially useful --- particularly when you are
-passing pointers to structures via a void * pointer.  The tty code,
-for example, does this frequently to pass driver-specific and line
-discipline-specific structures back and forth.
-
-The way to use magic numbers is to declare them at the beginning of
-the structure, like so::
-
-	struct tty_ldisc {
-		int	magic;
-		...
-	};
-
-Please follow this discipline when you are adding future enhancements
-to the kernel!  It has saved me countless hours of debugging,
-especially in the screwy cases where an array has been overrun and
-structures following the array have been overwritten.  Using this
-discipline, these cases get detected quickly and safely.
-
-Changelog::
-
-					Theodore Ts'o
-					31 Mar 94
-
-  The magic table is current to Linux 2.1.55.
-
-					Michael Chastain
-					<mailto:mec@shout.net>
-					22 Sep 1997
-
-  Now it should be up to date with Linux 2.1.112. Because
-  we are in feature freeze time it is very unlikely that
-  something will change before 2.2.x. The entries are
-  sorted by number field.
-
-					Krzysztof G. Baranowski
-					<mailto: kgb@knm.org.pl>
-					29 Jul 1998
-
-  Updated the magic table to Linux 2.5.45. Right over the feature freeze,
-  but it is possible that some new magic numbers will sneak into the
-  kernel before 2.6.x yet.
-
-					Petr Baudis
-					<pasky@ucw.cz>
-					03 Nov 2002
-
-  Updated the magic table to Linux 2.5.74.
-
-					Fabian Frederick
-					<ffrederick@users.sourceforge.net>
-					09 Jul 2003
-
-
-===================== ================ ======================== ==========================================
-Magic Name            Number           Structure                File
-===================== ================ ======================== ==========================================
-PG_MAGIC              'P'              pg_{read,write}_hdr      ``include/linux/pg.h``
-APM_BIOS_MAGIC        0x4101           apm_user                 ``arch/x86/kernel/apm_32.c``
-FASYNC_MAGIC          0x4601           fasync_struct            ``include/linux/fs.h``
-SLIP_MAGIC            0x5302           slip                     ``drivers/net/slip.h``
-BAYCOM_MAGIC          0x19730510       baycom_state             ``drivers/net/baycom_epp.c``
-HDLCDRV_MAGIC         0x5ac6e778       hdlcdrv_state            ``include/linux/hdlcdrv.h``
-KV_MAGIC              0x5f4b565f       kernel_vars_s            ``arch/mips/include/asm/sn/klkernvars.h``
-CODA_MAGIC            0xC0DAC0DA       coda_file_info           ``fs/coda/coda_fs_i.h``
-YAM_MAGIC             0xF10A7654       yam_port                 ``drivers/net/hamradio/yam.c``
-CCB_MAGIC             0xf2691ad2       ccb                      ``drivers/scsi/ncr53c8xx.c``
-QUEUE_MAGIC_FREE      0xf7e1c9a3       queue_entry              ``drivers/scsi/arm/queue.c``
-QUEUE_MAGIC_USED      0xf7e1cc33       queue_entry              ``drivers/scsi/arm/queue.c``
-NMI_MAGIC             0x48414d4d455201 nmi_s                    ``arch/mips/include/asm/sn/nmi.h``
-===================== ================ ======================== ==========================================