Orange Pi5 kernel

^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   2) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   3) ====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   4) kAFS: AFS FILESYSTEM
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   5) ====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   6) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   7) .. Contents:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   8) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300   9)  - Overview.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  10)  - Usage.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  11)  - Mountpoints.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  12)  - Dynamic root.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  13)  - Proc filesystem.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  14)  - The cell database.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  15)  - Security.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  16)  - The @sys substitution.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  17) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  18) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  19) Overview
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  20) ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  21) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  22) This filesystem provides a fairly simple secure AFS filesystem driver. It is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  23) under development and does not yet provide the full feature set.  The features
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  24) it does support include:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  25) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  26)  (*) Security (currently only AFS kaserver and KerberosIV tickets).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  27) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  28)  (*) File reading and writing.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  29) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  30)  (*) Automounting.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  31) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  32)  (*) Local caching (via fscache).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  33) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  34) It does not yet support the following AFS features:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  35) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  36)  (*) pioctl() system call.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  37) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  38) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  39) Compilation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  40) ===========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  41) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  42) The filesystem should be enabled by turning on the kernel configuration
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  43) options::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  44) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  45) 	CONFIG_AF_RXRPC		- The RxRPC protocol transport
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  46) 	CONFIG_RXKAD		- The RxRPC Kerberos security handler
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  47) 	CONFIG_AFS		- The AFS filesystem
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  48) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  49) Additionally, the following can be turned on to aid debugging::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  50) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  51) 	CONFIG_AF_RXRPC_DEBUG	- Permit AF_RXRPC debugging to be enabled
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  52) 	CONFIG_AFS_DEBUG	- Permit AFS debugging to be enabled
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  53) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  54) They permit the debugging messages to be turned on dynamically by manipulating
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  55) the masks in the following files::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  56) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  57) 	/sys/module/af_rxrpc/parameters/debug
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  58) 	/sys/module/kafs/parameters/debug
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  59) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  60) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  61) Usage
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  62) =====
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  63) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  64) When inserting the driver modules the root cell must be specified along with a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  65) list of volume location server IP addresses::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  66) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  67) 	modprobe rxrpc
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  68) 	modprobe kafs rootcell=cambridge.redhat.com:172.16.18.73:172.16.18.91
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  69) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  70) The first module is the AF_RXRPC network protocol driver.  This provides the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  71) RxRPC remote operation protocol and may also be accessed from userspace.  See:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  72) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  73) 	Documentation/networking/rxrpc.rst
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  74) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  75) The second module is the kerberos RxRPC security driver, and the third module
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  76) is the actual filesystem driver for the AFS filesystem.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  77) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  78) Once the module has been loaded, more modules can be added by the following
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  79) procedure::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  80) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  81) 	echo add grand.central.org 18.9.48.14:128.2.203.61:130.237.48.87 >/proc/fs/afs/cells
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  82) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  83) Where the parameters to the "add" command are the name of a cell and a list of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  84) volume location servers within that cell, with the latter separated by colons.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  85) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  86) Filesystems can be mounted anywhere by commands similar to the following::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  87) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  88) 	mount -t afs "%cambridge.redhat.com:root.afs." /afs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  89) 	mount -t afs "#cambridge.redhat.com:root.cell." /afs/cambridge
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  90) 	mount -t afs "#root.afs." /afs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  91) 	mount -t afs "#root.cell." /afs/cambridge
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  92) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  93) Where the initial character is either a hash or a percent symbol depending on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  94) whether you definitely want a R/W volume (percent) or whether you'd prefer a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  95) R/O volume, but are willing to use a R/W volume instead (hash).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  96) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  97) The name of the volume can be suffixes with ".backup" or ".readonly" to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  98) specify connection to only volumes of those types.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300  99) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100) The name of the cell is optional, and if not given during a mount, then the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) named volume will be looked up in the cell specified during modprobe.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103) Additional cells can be added through /proc (see later section).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) Mountpoints
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) ===========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) AFS has a concept of mountpoints. In AFS terms, these are specially formatted
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) symbolic links (of the same form as the "device name" passed to mount).  kAFS
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) presents these to the user as directories that have a follow-link capability
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) (ie: symbolic link semantics).  If anyone attempts to access them, they will
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) automatically cause the target volume to be mounted (if possible) on that site.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) Automatically mounted filesystems will be automatically unmounted approximately
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) twenty minutes after they were last used.  Alternatively they can be unmounted
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117) directly with the umount() system call.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) Manually unmounting an AFS volume will cause any idle submounts upon it to be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) culled first.  If all are culled, then the requested volume will also be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) unmounted, otherwise error EBUSY will be returned.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) This can be used by the administrator to attempt to unmount the whole AFS tree
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) mounted on /afs in one go by doing::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) 	umount /afs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) Dynamic Root
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) ============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) A mount option is available to create a serverless mount that is only usable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) for dynamic lookup.  Creating such a mount can be done by, for example::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) 	mount -t afs none /afs -o dyn
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137) This creates a mount that just has an empty directory at the root.  Attempting
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) to look up a name in this directory will cause a mountpoint to be created that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) looks up a cell of the same name, for example::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) 	ls /afs/grand.central.org/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) Proc Filesystem
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) ===============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) The AFS modules creates a "/proc/fs/afs/" directory and populates it:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149)   (*) A "cells" file that lists cells currently known to the afs module and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150)       their usage counts::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) 	[root@andromeda ~]# cat /proc/fs/afs/cells
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) 	USE NAME
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154) 	  3 cambridge.redhat.com
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156)   (*) A directory per cell that contains files that list volume location
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157)       servers, volumes, and active servers known within that cell::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159) 	[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/servers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) 	USE ADDR            STATE
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) 	  4 172.16.18.91        0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) 	[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/vlservers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) 	ADDRESS
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164) 	172.16.18.91
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165) 	[root@andromeda ~]# cat /proc/fs/afs/cambridge.redhat.com/volumes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) 	USE STT VLID[0]  VLID[1]  VLID[2]  NAME
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) 	  1 Val 20000000 20000001 20000002 root.afs
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) The Cell Database
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171) =================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) The filesystem maintains an internal database of all the cells it knows and the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174) IP addresses of the volume location servers for those cells.  The cell to which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175) the system belongs is added to the database when modprobe is performed by the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176) "rootcell=" argument or, if compiled in, using a "kafs.rootcell=" argument on
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177) the kernel command line.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179) Further cells can be added by commands similar to the following::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181) 	echo add CELLNAME VLADDR[:VLADDR][:VLADDR]... >/proc/fs/afs/cells
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182) 	echo add grand.central.org 18.9.48.14:128.2.203.61:130.237.48.87 >/proc/fs/afs/cells
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184) No other cell database operations are available at this time.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187) Security
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) Secure operations are initiated by acquiring a key using the klog program.  A
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191) very primitive klog program is available at:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) 	https://people.redhat.com/~dhowells/rxrpc/klog.c
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) This should be compiled by::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197) 	make klog LDLIBS="-lcrypto -lcrypt -lkrb4 -lkeyutils"
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) And then run as::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) 	./klog
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) Assuming it's successful, this adds a key of type RxRPC, named for the service
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) and cell, eg: "afs@<cellname>".  This can be viewed with the keyctl program or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205) by cat'ing /proc/keys::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) 	[root@andromeda ~]# keyctl show
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) 	Session Keyring
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209) 	       -3 --alswrv      0     0  keyring: _ses.3268
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) 		2 --alswrv      0     0   \_ keyring: _uid.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) 	111416553 --als--v      0     0   \_ rxrpc: afs@CAMBRIDGE.REDHAT.COM
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) Currently the username, realm, password and proposed ticket lifetime are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214) compiled in to the program.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216) It is not required to acquire a key before using AFS facilities, but if one is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) not acquired then all operations will be governed by the anonymous user parts
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218) of the ACLs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220) If a key is acquired, then all AFS operations, including mounts and automounts,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221) made by a possessor of that key will be secured with that key.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 223) If a file is opened with a particular key and then the file descriptor is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 224) passed to a process that doesn't have that key (perhaps over an AF_UNIX
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 225) socket), then the operations on the file will be made with key that was used to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 226) open the file.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 227) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 228) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 229) The @sys Substitution
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 230) =====================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 231) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 232) The list of up to 16 @sys substitutions for the current network namespace can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 233) be configured by writing a list to /proc/fs/afs/sysname::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 234) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 235) 	[root@andromeda ~]# echo foo amd64_linux_26 >/proc/fs/afs/sysname
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 236) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 237) or cleared entirely by writing an empty list::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 238) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 239) 	[root@andromeda ~]# echo >/proc/fs/afs/sysname
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 240) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 241) The current list for current network namespace can be retrieved by::
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 242) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 243) 	[root@andromeda ~]# cat /proc/fs/afs/sysname
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 244) 	foo
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 245) 	amd64_linux_26
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 246) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 247) When @sys is being substituted for, each element of the list is tried in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 248) order given.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 249) 
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 250) By default, the list will contain one item that conforms to the pattern
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 251) "<arch>_linux_26", amd64 being the name for x86_64.