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Ahelenia Ziemiańska d391615618 kernel: relay: remove relay_file_splice_read dead code, doesn't work 
Documentation/filesystems/relay.rst says to use
	return debugfs_create_file(filename, mode, parent, buf,
	                           &relay_file_operations);
and this is the only way relay_file_operations is used.

Thus: debugfs_create_file(&relay_file_operations)
   -> __debugfs_create_file(&debugfs_full_proxy_file_operations,
                            &relay_file_operations)
   -> dentry{inode: {i_fop: &debugfs_full_proxy_file_operations},
             d_fsdata: &relay_file_operations
                       | DEBUGFS_FSDATA_IS_REAL_FOPS_BIT}

debugfs_full_proxy_file_operations.open is full_proxy_open, which extracts
the &relay_file_operations from the dentry, and allocates via
__full_proxy_fops_init() new fops, with trivial wrappers around release,
llseek, read, write, poll, and unlocked_ioctl, then replaces the fops on
the opened file therewith.

Naturally, all thusly-created debugfs files have .splice_read = NULL. 
This was introduced in commit 49d200deaa ("debugfs: prevent access to
removed files' private data") from 2016-03-22.

AFAICT, relay_file_operations is the only struct file_operations used for
debugfs which defines a .splice_read callback.  Hooking it up with

>	diff --git a/fs/debugfs/file.c b/fs/debugfs/file.c
>	index 5063434be0fc..952fcf5b2afa 100644
>	--- a/fs/debugfs/file.c
>	+++ b/fs/debugfs/file.c
>	@@ -328,6 +328,11 @@ FULL_PROXY_FUNC(write, ssize_t, filp,
>	 			loff_t *ppos),
>	 		ARGS(filp, buf, size, ppos));
>
>	+FULL_PROXY_FUNC(splice_read, long, in,
>	+		PROTO(struct file *in, loff_t *ppos, struct pipe_inode_info *pipe,
>	+			size_t len, unsigned int flags),
>	+		ARGS(in, ppos, pipe, len, flags));
>	+
>	 FULL_PROXY_FUNC(unlocked_ioctl, long, filp,
>	 		PROTO(struct file *filp, unsigned int cmd, unsigned long arg),
>	 		ARGS(filp, cmd, arg));
>	@@ -382,6 +387,8 @@ static void __full_proxy_fops_init(struct file_operations *proxy_fops,
>	 		proxy_fops->write = full_proxy_write;
>	 	if (real_fops->poll)
>	 		proxy_fops->poll = full_proxy_poll;
>	+	if (real_fops->splice_read)
>	+		proxy_fops->splice_read = full_proxy_splice_read;
>	 	if (real_fops->unlocked_ioctl)
>	 		proxy_fops->unlocked_ioctl = full_proxy_unlocked_ioctl;
>	 }

shows it just doesn't work, and splicing always instantly returns empty
(subsequent reads actually return the contents).

No-one noticed it became dead code in 2016, who knows if it worked back
then. Clearly no-one cares; just delete it.

Link: https://lkml.kernel.org/r/dtexwpw6zcdx7dkx3xj5gyjp5syxmyretdcbcdtvrnukd4vvuh@tarta.nabijaczleweli.xyz
Signed-off-by: Ahelenia Ziemiańska <nabijaczleweli@nabijaczleweli.xyz>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Li kunyu <kunyu@nfschina.com>
Cc: Mike Rapoport (IBM) <rppt@kernel.org>
Cc: Rafael J. Wysocki <rafael@kernel.org>
Cc: Suren Baghdasaryan <surenb@google.com>
Cc: Zhang Zhengming <zhang.zhengming@h3c.com>
Cc: Zhao Lei <zhao_lei1@hoperun.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
History 2023-12-29 12:22:27 -08:00
arch x86/kexec: simplify the logic of mem_region_callback() 2023-12-20 15:02:58 -08:00
block block-6.7-2023-12-01 2023-12-02 06:39:30 +09:00
certs This update includes the following changes: 2023-11-02 16:15:30 -10:00
crypto This push fixes a regression in ahash and hides the Kconfig sub-options for the jitter RNG. 2023-11-09 17:04:58 -08:00
Documentation docs: submit-checklist: remove all of "make namespacecheck" 2023-12-29 12:22:27 -08:00
drivers lib: crc_ccitt_false() is identical to crc_itu_t() 2023-12-29 12:22:26 -08:00
fs nilfs2: switch WARN_ONs to warning output in nilfs_sufile_do_free() 2023-12-20 15:02:58 -08:00
include lib: crc_ccitt_false() is identical to crc_itu_t() 2023-12-29 12:22:26 -08:00
init init/Kconfig: move more items into the EXPERT menu 2023-12-20 15:02:58 -08:00
io_uring io_uring: use fget/fput consistently 2023-11-28 11:56:29 -07:00
ipc Many singleton patches against the MM code. The patch series which are 2023-11-02 19:38:47 -10:00
kernel kernel: relay: remove relay_file_splice_read dead code, doesn't work 2023-12-29 12:22:27 -08:00
lib lib: crc_ccitt_false() is identical to crc_itu_t() 2023-12-29 12:22:26 -08:00
LICENSES LICENSES: Add the copyleft-next-0.3.1 license 2022-11-08 15:44:01 +01:00
mm mm/mglru: reclaim offlined memcgs harder 2023-12-12 17:20:20 -08:00
net wireless fixes: 2023-11-29 19:43:34 -08:00
rust Kbuild updates for v6.7 2023-11-04 08:07:19 -10:00
samples Landlock updates for v6.7-rc1 2023-11-03 09:28:53 -10:00
scripts scripts/checkstack.pl: change min_stack to 512 by default 2023-12-29 12:22:27 -08:00
security kexec_file: print out debugging message if required 2023-12-20 15:02:57 -08:00
sound ALSA: hda: Disable power-save on KONTRON SinglePC 2023-11-30 16:14:21 +01:00
tools Revert "selftests: error out if kernel header files are not yet built" 2023-12-12 17:20:19 -08:00
usr usr/Kconfig: fix typos of "its" 2023-12-20 15:02:58 -08:00
virt ARM: 2023-09-07 13:52:20 -07:00
.clang-format iommu: Add for_each_group_device() 2023-05-23 08:15:51 +02:00
.cocciconfig scripts: add Linux .cocciconfig for coccinelle 2016-07-22 12:13:39 +02:00
.get_maintainer.ignore get_maintainer: add Alan to .get_maintainer.ignore 2022-08-20 15:17:44 -07:00
.gitattributes .gitattributes: set diff driver for Rust source code files 2023-05-31 17:48:25 +02:00
.gitignore kbuild: rpm-pkg: generate kernel.spec in rpmbuild/SPECS/ 2023-10-03 20:49:09 +09:00
.mailmap .mailmap: add a new address mapping for Chester Lin 2023-12-06 16:12:45 -08:00
.rustfmt.toml rust: add .rustfmt.toml 2022-09-28 09:02:20 +02:00
COPYING COPYING: state that all contributions really are covered by this file 2020-02-10 13:32:20 -08:00
CREDITS MAINTAINERS: remove Ohad Ben-Cohen from hwspinlock subsystem 2023-12-29 12:22:24 -08:00
Kbuild Kbuild updates for v6.1 2022-10-10 12:00:45 -07:00
Kconfig kbuild: ensure full rebuild when the compiler is updated 2020-05-12 13:28:33 +09:00
MAINTAINERS MAINTAINERS: remove Ohad Ben-Cohen from hwspinlock subsystem 2023-12-29 12:22:24 -08:00
Makefile checkstack: allow to pass MINSTACKSIZE parameter 2023-12-10 17:21:32 -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.