linux-kernel - [PATCH] vfs: Add PERM_* symbolic helpers for common file mode/permissions

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Date:   Mon, 27 Nov 2017 11:06:35 +0100
From:   Ingo Molnar <mingo@...nel.org>
To:     Peter Zijlstra <peterz@...radead.org>,
        Linus Torvalds <torvalds@...ux-foundation.org>
Cc:     Thomas Gleixner <tglx@...utronix.de>,
        LKML <linux-kernel@...r.kernel.org>,
        Dave Hansen <dave.hansen@...ux.intel.com>,
        Andy Lutomirski <luto@...nel.org>,
        Borislav Petkov <bp@...en8.de>,
        Brian Gerst <brgerst@...il.com>,
        Denys Vlasenko <dvlasenk@...hat.com>,
        "H. Peter Anvin" <hpa@...or.com>,
        Josh Poimboeuf <jpoimboe@...hat.com>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Rik van Riel <riel@...hat.com>, daniel.gruss@...k.tugraz.at,
        hughd@...gle.com, keescook@...gle.com, linux-mm@...ck.org,
        michael.schwarz@...k.tugraz.at, moritz.lipp@...k.tugraz.at,
        richard.fellner@...dent.tugraz.at
Subject: [PATCH] vfs: Add PERM_* symbolic helpers for common file
 mode/permissions


* Peter Zijlstra <peterz@...radead.org> wrote:

> On Mon, Nov 27, 2017 at 12:14:07AM +0100, Thomas Gleixner wrote:
> >  static int __init pt_dump_debug_init(void)
> >  {
> > +	pe_knl = debugfs_create_file("kernel_page_tables", S_IRUSR, NULL, NULL,
> > +				     &ptdump_fops);
> > +	if (!pe_knl)
> >  		return -ENOMEM;
> >  
> > +	pe_curknl = debugfs_create_file("current_page_tables_knl", S_IRUSR,
> > +					NULL, NULL, &ptdump_curknl_fops);
> > +	if (!pe_curknl)
> > +		goto err;
> > +
> > +#ifdef CONFIG_KAISER
> > +	pe_curusr = debugfs_create_file("current_page_tables_usr", S_IRUSR,
> > +					NULL, NULL, &ptdump_curusr_fops);
> > +	if (!pe_curusr)
> > +		goto err;
> > +#endif
> >  	return 0;
> > +err:
> > +	pt_dump_debug_remove_files();
> > +	return -ENOMEM;
> >  }
> 
> 
> Could we pretty please use the octal permission thing? I can't read
> thise S_crap nonsense.

They are completely unreadable to me too. So if we added these helpers I sent a 
year ago:

	https://lwn.net/Articles/696231/

Then the above could be written as:

	pe_curknl = debugfs_create_file("current_page_tables_knl", PERM_r________,
					NULL, NULL, &ptdump_curknl_fops);

... etc., which is much more readable IMHO. Not only that, it would be trivial to 
_write_ permission masks as well. I just wrote this:

	PERM_rw_r__r__

Which is so much more readable than "S_IRUGO|S_IWUSR" or even "0644". The former 
pattern is used 527 times in the kernel ...

The patch below adds it to the current kernel.

Thanks,

	Ingo
---
Signed-off-by: Ingo Molnar <mingo@...nel.org>

 include/linux/stat.h | 32 ++++++++++++++++++++++++++++++++
 1 file changed, 32 insertions(+)

diff --git a/include/linux/stat.h b/include/linux/stat.h
index 22484e44544d..fc389c3a8692 100644
--- a/include/linux/stat.h
+++ b/include/linux/stat.h
@@ -6,6 +6,38 @@
 #include <asm/stat.h>
 #include <uapi/linux/stat.h>
 
+/*
+ * Human readable symbolic definitions for common
+ * file permissions:
+ */
+#define PERM_r________	0400
+#define PERM_r__r_____	0440
+#define PERM_r__r__r__	0444
+
+#define PERM_rw_______	0600
+#define PERM_rw_r_____	0640
+#define PERM_rw_r__r__	0644
+#define PERM_rw_rw_r__	0664
+#define PERM_rw_rw_rw_	0666
+
+#define PERM__w_______	0200
+#define PERM__w__w____	0220
+#define PERM__w__w__w_	0222
+
+#define PERM_r_x______	0500
+#define PERM_r_xr_x___	0550
+#define PERM_r_xr_xr_x	0555
+
+#define PERM_rwx______	0700
+#define PERM_rwxr_x___	0750
+#define PERM_rwxr_xr_x	0755
+#define PERM_rwxrwxr_x	0775
+#define PERM_rwxrwxrwx	0777
+
+#define PERM__wx______	0300
+#define PERM__wx_wx___	0330
+#define PERM__wx_wx_wx	0333
+
 #define S_IRWXUGO	(S_IRWXU|S_IRWXG|S_IRWXO)
 #define S_IALLUGO	(S_ISUID|S_ISGID|S_ISVTX|S_IRWXUGO)
 #define S_IRUGO		(S_IRUSR|S_IRGRP|S_IROTH)