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Christian Brauner b6c770d7c9 binderfs: make each binderfs mount a new instance
When currently mounting binderfs in the same ipc namespace twice:

mount -t binder binder /A
mount -t binder binder /B

then the binderfs instances mounted on /A and /B will be the same, i.e.
they will have the same superblock. This was the first approach that seemed
reasonable. However, this leads to some problems and inconsistencies:

/* private binderfs instance in same ipc namespace */
There is no way for a user to request a private binderfs instance in the
same ipc namespace.
This request has been made in a private mail to me by two independent
people.

/* bind-mounts */
If users want the same binderfs instance to appear in multiple places they
can use bind mounts. So there is no value in having a request for a new
binderfs mount giving them the same instance.

/* unexpected behavior */
It's surprising that request to mount binderfs is not giving the user a new
instance like tmpfs, devpts, ramfs, and others do.

/* past mistakes */
Other pseudo-filesystems once made the same mistakes of giving back the
same superblock when actually requesting a new mount (cf. devpts's
deprecated "newinstance" option).
We should not make the same mistake. Once we've committed to always giving
back the same superblock in the same IPC namespace with the next kernel
release we will not be able to make that change so better to do it now.

/* kdbusfs */
It was pointed out to me that kdbusfs - which is conceptually closely
related to binderfs - also allowed users to get a private kdbusfs instance
in the same IPC namespace by making each mount of kdbusfs a separate
instance. I think that makes a lot of sense.

Signed-off-by: Christian Brauner <christian.brauner@ubuntu.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
2019-01-08 16:01:53 +01:00
Documentation Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
LICENSES This is a fairly typical cycle for documentation. There's some welcome 2018-10-24 18:01:11 +01:00
arch Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
block for-4.21/block-20190102 2019-01-02 18:49:58 -08:00
certs kbuild: remove redundant target cleaning on failure 2019-01-06 09:46:51 +09:00
crypto Kconfig updates for v4.21 2018-12-29 13:03:29 -08:00
drivers binderfs: make each binderfs mount a new instance 2019-01-08 16:01:53 +01:00
firmware kbuild: change filechk to surround the given command with { } 2019-01-06 09:46:51 +09:00
fs Add Adiantum support for fscrypt 2019-01-06 12:21:11 -08:00
include Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
init jump_label: move 'asm goto' support test to Kconfig 2019-01-06 09:46:51 +09:00
ipc ipc: IPCMNI limit check for semmni 2018-10-31 08:54:14 -07:00
kernel Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
lib Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
mm Change mincore() to count "mapped" pages rather than "cached" pages 2019-01-06 13:43:02 -08:00
net jump_label: move 'asm goto' support test to Kconfig 2019-01-06 09:46:51 +09:00
samples Merge branch 'for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/hid/hid 2019-01-05 17:53:40 -08:00
scripts kconfig: rename generated .*conf-cfg to *conf-cfg 2019-01-06 10:47:09 +09:00
security Merge branch 'mount.part1' of git://git.kernel.org/pub/scm/linux/kernel/git/viro/vfs 2019-01-05 13:25:58 -08:00
sound Remove 'type' argument from access_ok() function 2019-01-03 18:57:57 -08:00
tools Kbuild late updates for v4.21 2019-01-06 16:33:10 -08:00
usr user/Makefile: Fix typo and capitalization in comment section 2018-12-11 00:18:03 +09:00
virt Merge branch 'akpm' (patches from Andrew) 2019-01-05 09:16:18 -08:00
.clang-format page cache: Convert find_get_pages_contig to XArray 2018-10-21 10:46:34 -04:00
.cocciconfig
.get_maintainer.ignore
.gitattributes .gitattributes: set git diff driver for C source code files 2016-10-07 18:46:30 -07:00
.gitignore kbuild: Add support for DT binding schema checks 2018-12-13 09:41:32 -06:00
.mailmap A few early MIPS fixes for 4.21: 2019-01-05 12:48:25 -08:00
COPYING COPYING: use the new text with points to the license files 2018-03-23 12:41:45 -06:00
CREDITS Add CREDITS entry for Shaohua Li 2019-01-04 14:27:09 -07:00
Kbuild kbuild: use assignment instead of define ... endef for filechk_* rules 2019-01-06 10:22:35 +09:00
Kconfig kconfig: move the "Executable file formats" menu to fs/Kconfig.binfmt 2018-08-02 08:06:55 +09:00
MAINTAINERS chrome platform changes for v4.21 2019-01-06 11:40:06 -08:00
Makefile Linux 5.0-rc1 2019-01-06 17:08:20 -08:00
README Drop all 00-INDEX files from Documentation/ 2018-09-09 15:08:58 -06:00

README

Linux kernel
============

There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.

In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``.  The formatted documentation can also be read online at:

    https://www.kernel.org/doc/html/latest/

There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.

Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.