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Date:   Mon, 14 Aug 2023 16:08:29 -0700
From:   "Paul E. McKenney" <paulmck@kernel.org>
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Alexey Dobriyan <adobriyan@gmail.com>, akpm@linux-foundation.org,
        arnd@kernel.org, ndesaulniers@google.com, sfr@canb.auug.org.au,
        linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org,
        kernel-team@meta.com
Subject: Re: [PATCH RFC bootconfig] 1/2] fs/proc: Add /proc/cmdline_load for
 boot loader arguments
Message-ID: <79d0ddcf-3b20-48f5-89f6-7eb5c3fa4c88@paulmck-laptop>
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On Sat, Aug 12, 2023 at 04:30:41PM -0700, Paul E. McKenney wrote:
> On Sun, Aug 06, 2023 at 09:39:28PM -0700, Paul E. McKenney wrote:
> > On Mon, Aug 07, 2023 at 11:44:55AM +0900, Masami Hiramatsu wrote:
> > > On Fri, 4 Aug 2023 10:36:17 -0700
> > > "Paul E. McKenney" <paulmck@kernel.org> wrote:
> > > 
> > > > On Fri, Aug 04, 2023 at 08:23:20PM +0300, Alexey Dobriyan wrote:
> > > > > On Thu, Jul 27, 2023 at 08:37:00PM -0700, Paul E. McKenney wrote:
> > > > > > In kernels built with CONFIG_BOOT_CONFIG_FORCE=y, /proc/cmdline will
> > > > > > show all kernel boot parameters, both those supplied by the boot loader
> > > > > > and those embedded in the kernel image.  This works well for those who
> > > > > > just want to see all of the kernel boot parameters, but is not helpful to
> > > > > > those who need to see only those parameters supplied by the boot loader.
> > > > > > This is especially important when these parameters are presented to the
> > > > > > boot loader by automation that might gather them from diverse sources.
> > > > > > 
> > > > > > Therefore, provide a /proc/cmdline_load file that shows only those kernel
> > > > > > boot parameters supplied by the boot loader.
> > > > > 
> > > > > > +static int cmdline_load_proc_show(struct seq_file *m, void *v)
> > > > > > +{
> > > > > > +	seq_puts(m, boot_command_line);
> > > > > > +	seq_putc(m, '\n');
> > > > > > +	return 0;
> > > > > > +}
> > > > > > +
> > > > > >  static int __init proc_cmdline_init(void)
> > > > > >  {
> > > > > >  	struct proc_dir_entry *pde;
> > > > > > @@ -19,6 +27,11 @@ static int __init proc_cmdline_init(void)
> > > > > >  	pde = proc_create_single("cmdline", 0, NULL, cmdline_proc_show);
> > > > > >  	pde_make_permanent(pde);
> > > > > >  	pde->size = saved_command_line_len + 1;
> > > > > > +	if (IS_ENABLED(CONFIG_BOOT_CONFIG_FORCE)) {
> > > > > > +		pde = proc_create_single("cmdline_load", 0, NULL, cmdline_load_proc_show);
> > > > > > +		pde_make_permanent(pde);
> > > > > > +		pde->size = strnlen(boot_command_line, COMMAND_LINE_SIZE) + 1;
> > > > > > +	}
> > > > > 
> > > > > Please add it as separate fs/proc/cmdline_load.c file so that name of
> > > > > the file matches name of the /proc file.
> > > > 
> > > > Thank you, will do!
> > > > 
> > > > > The name "cmdline_load" is kind of non-descriptive. Mentioning "bootloader"
> > > > > somewhere should improve things.
> > > > 
> > > > If we can all quickly come to agreement on a name, I can of course easily
> > > > change it.
> > > > 
> > > > /proc/cmdline_bootloader?  Better than /proc/cmdline_from_bootloader,
> > > > I suppose.  /proc/cmdline_bootldr?  /proc/bootloader by analogy with
> > > > /proc/bootconfig?  Something else?
> > > 
> > > What about "/proc/raw_cmdline" ?
> > 
> > That would work of me!
> > 
> > Any objections to /proc/raw_cmdline?
> > 
> > Going once...
> 
> Going twice...
> 
> If I don't hear otherwise, /proc/raw_cmdline is is on Monday August 14 PDT.

And gone!

Please see below for the updated version.

								Thanx, Paul

------------------------------------------------------------------------

commit 0fe10f0d1873a6f6e287c0c5b45e9203b0e33c83
Author: Paul E. McKenney <paulmck@kernel.org>
Date:   Fri Jul 21 16:05:38 2023 -0700

    fs/proc: Add /proc/raw_cmdline for boot loader arguments
    
    In kernels built with CONFIG_BOOT_CONFIG_FORCE=y, /proc/cmdline will
    show all kernel boot parameters, both those supplied by the boot loader
    and those embedded in the kernel image.  This works well for those who
    just want to see all of the kernel boot parameters, but is not helpful to
    those who need to see only those parameters supplied by the boot loader.
    This is especially important when these parameters are presented to the
    boot loader by automation that might gather them from diverse sources.
    It is also useful when booting the next kernel via kexec(), in which
    case it is necessary to supply only those kernel command-line arguments
    from the boot loader, and most definitely not those that were embedded
    into the current kernel.
    
    Therefore, provide a /proc/raw_cmdline file that shows only those kernel
    boot parameters supplied by the boot loader.
    
    Why put this in /proc?  Because it is quite similar to /proc/cmdline,
    and /proc/bootconfig, so it makes sense to put it in the same place that
    those files are located.
    
    [ sfr: Apply kernel test robot feedback. ]
    [ paulmck: Apply Randy Dunlap feedback. ]
    [ paulmck: Apply naming feedback from Alexey Dobriyan and Masami Hiramatsu. ]
    
    Co-developed-by: Stephen Rothwell <sfr@canb.auug.org.au>
    Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
    Co-developed-by: Arnd Bergmann <arnd@kernel.org>
    Signed-off-by: Arnd Bergmann <arnd@kernel.org>
    Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
    Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
    Acked-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
    Cc: Andrew Morton <akpm@linux-foundation.org>
    Cc: Alexey Dobriyan <adobriyan@gmail.com>
    Cc: <linux-fsdevel@vger.kernel.org>

diff --git a/Documentation/filesystems/proc.rst b/Documentation/filesystems/proc.rst
index 75a8c899ebcc..61419270c38f 100644
--- a/Documentation/filesystems/proc.rst
+++ b/Documentation/filesystems/proc.rst
@@ -723,6 +723,7 @@ files are there, and which are missing.
  partitions   Table of partitions known to the system
  pci 	      Deprecated info of PCI bus (new way -> /proc/bus/pci/,
               decoupled by lspci				(2.4)
+ raw_cmdline  Kernel command line obtained from kernel image	(6.6)
  rtc          Real time clock
  scsi         SCSI info (see text)
  slabinfo     Slab pool info
diff --git a/fs/proc/Makefile b/fs/proc/Makefile
index bd08616ed8ba..6182296f3c6b 100644
--- a/fs/proc/Makefile
+++ b/fs/proc/Makefile
@@ -34,3 +34,4 @@ proc-$(CONFIG_PROC_VMCORE)	+= vmcore.o
 proc-$(CONFIG_PRINTK)	+= kmsg.o
 proc-$(CONFIG_PROC_PAGE_MONITOR)	+= page.o
 proc-$(CONFIG_BOOT_CONFIG)	+= bootconfig.o
+proc-$(CONFIG_BOOT_CONFIG_FORCE)	+= raw_cmdline.o
diff --git a/fs/proc/raw_cmdline.c b/fs/proc/raw_cmdline.c
new file mode 100644
index 000000000000..2e19eb89fc8e
--- /dev/null
+++ b/fs/proc/raw_cmdline.c
@@ -0,0 +1,25 @@
+// SPDX-License-Identifier: GPL-2.0
+#include <linux/fs.h>
+#include <linux/init.h>
+#include <linux/proc_fs.h>
+#include <linux/seq_file.h>
+#include <asm/setup.h>
+#include "internal.h"
+
+static int raw_cmdline_proc_show(struct seq_file *m, void *v)
+{
+	seq_puts(m, boot_command_line);
+	seq_putc(m, '\n');
+	return 0;
+}
+
+static int __init proc_raw_cmdline_init(void)
+{
+	struct proc_dir_entry *pde;
+
+	pde = proc_create_single("raw_cmdline", 0, NULL, raw_cmdline_proc_show);
+	pde_make_permanent(pde);
+	pde->size = strnlen(boot_command_line, COMMAND_LINE_SIZE) + 1;
+	return 0;
+}
+fs_initcall(proc_raw_cmdline_init);
diff --git a/include/linux/init.h b/include/linux/init.h
index 266c3e1640d4..29e75bbe7984 100644
--- a/include/linux/init.h
+++ b/include/linux/init.h
@@ -112,6 +112,7 @@
 #define __REFCONST       .section       ".ref.rodata", "a"
 
 #ifndef __ASSEMBLY__
+
 /*
  * Used for initialization calls..
  */
@@ -143,7 +144,7 @@ struct file_system_type;
 
 /* Defined in init/main.c */
 extern int do_one_initcall(initcall_t fn);
-extern char __initdata boot_command_line[];
+extern char boot_command_line[];
 extern char *saved_command_line;
 extern unsigned int saved_command_line_len;
 extern unsigned int reset_devices;
diff --git a/init/main.c b/init/main.c
index ad920fac325c..2121685c479a 100644
--- a/init/main.c
+++ b/init/main.c
@@ -135,7 +135,7 @@ EXPORT_SYMBOL(system_state);
 void (*__initdata late_time_init)(void);
 
 /* Untouched command line saved by arch-specific code. */
-char __initdata boot_command_line[COMMAND_LINE_SIZE];
+char boot_command_line[COMMAND_LINE_SIZE] __ro_after_init;
 /* Untouched saved command line (eg. for /proc) */
 char *saved_command_line __ro_after_init;
 unsigned int saved_command_line_len __ro_after_init;