diff mbox series

fs: move and constify sysctl_nr_open_min, sysctl_nr_open_max

Message ID 02591c1e-936b-46bf-ad2b-402b33338eee@p183
State New
Headers
Series fs: move and constify sysctl_nr_open_min, sysctl_nr_open_max |

Commit Message

Alexey Dobriyan Oct. 11, 2023, 6:24 p.m. UTC 
  sysctl_nr_open_min, sysctl_nr_open_max variables are really hard limits
on fs.nr_open sysctl, they aren't interesting to the rest of the code
and are constants (sysctl_nr_open is not constant obviously).

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
---

 fs/file.c            |    5 -----
 fs/file_table.c      |   10 ++++++++--
 include/linux/file.h |    2 --
 3 files changed, 8 insertions(+), 9 deletions(-)

Comments

David Laight Oct. 12, 2023, 1:54 p.m. UTC | #1 
From: Alexey Dobriyan
> Sent: 11 October 2023 19:24
> 
> sysctl_nr_open_min, sysctl_nr_open_max variables are really hard limits
> on fs.nr_open sysctl, they aren't interesting to the rest of the code
> and are constants (sysctl_nr_open is not constant obviously).
> 
> Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
> ---
> 
>  fs/file.c            |    5 -----
>  fs/file_table.c      |   10 ++++++++--
>  include/linux/file.h |    2 --
>  3 files changed, 8 insertions(+), 9 deletions(-)
> 
> --- a/fs/file.c
> +++ b/fs/file.c
> @@ -25,11 +25,6 @@
>  #include "internal.h"
> 
>  unsigned int sysctl_nr_open __read_mostly = 1024*1024;
> -unsigned int sysctl_nr_open_min = BITS_PER_LONG;
> -/* our min() is unusable in constant expressions ;-/ */
> -#define __const_min(x, y) ((x) < (y) ? (x) : (y))
> -unsigned int sysctl_nr_open_max =
> -	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
> 
>  static void __free_fdtable(struct fdtable *fdt)
>  {
> --- a/fs/file_table.c
> +++ b/fs/file_table.c
> @@ -111,6 +111,12 @@ static int proc_nr_files(struct ctl_table *table, int write, void *buffer,
>  	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
>  }
> 
> +static const unsigned int sysctl_nr_open_min = BITS_PER_LONG;
> +/* our min() is unusable in constant expressions ;-/ */
> +#define __const_min(x, y) ((x) < (y) ? (x) : (y))
> +static const unsigned int sysctl_nr_open_max =
> +	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;

I think you'll find that min() is fine.

Although those upper limits look suspect to me.
Looks like ~0.5G on 32bit and ~2G on 64bit based on the size of a bitmap?
But the kernel will run out of address space much earlier - esp on 32bit.

	David

 

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
Alexey Dobriyan Oct. 14, 2023, 9:22 a.m. UTC | #2 
On Thu, Oct 12, 2023 at 01:54:06PM +0000, David Laight wrote:
> From: Alexey Dobriyan
> > Sent: 11 October 2023 19:24

> > +/* our min() is unusable in constant expressions ;-/ */
> > +#define __const_min(x, y) ((x) < (y) ? (x) : (y))
> > +static const unsigned int sysctl_nr_open_max =
> > +	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
> 
> I think you'll find that min() is fine.

Mainline min() still can't do

	static const x = min(1, 2);
David Laight Oct. 15, 2023, 9:16 a.m. UTC | #3 
From: Alexey Dobriyan
> Sent: 14 October 2023 10:23
> 
> On Thu, Oct 12, 2023 at 01:54:06PM +0000, David Laight wrote:
> > From: Alexey Dobriyan
> > > Sent: 11 October 2023 19:24
> 
> > > +/* our min() is unusable in constant expressions ;-/ */
> > > +#define __const_min(x, y) ((x) < (y) ? (x) : (y))
> > > +static const unsigned int sysctl_nr_open_max =
> > > +	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
> >
> > I think you'll find that min() is fine.
> 
> Mainline min() still can't do
> 
> 	static const x = min(1, 2);

There has been a whole load of stuff that is supposed to do that
for ages - my changes don't affect it.

I presume they work - because they make it horribly complicated.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
David Laight Oct. 15, 2023, 9:30 a.m. UTC | #4 
From: Alexey Dobriyan
> Sent: 14 October 2023 10:23
> 
> On Thu, Oct 12, 2023 at 01:54:06PM +0000, David Laight wrote:
> > From: Alexey Dobriyan
> > > Sent: 11 October 2023 19:24
> 
> > > +/* our min() is unusable in constant expressions ;-/ */
> > > +#define __const_min(x, y) ((x) < (y) ? (x) : (y))
> > > +static const unsigned int sysctl_nr_open_max =
> > > +	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
> >
> > I think you'll find that min() is fine.
> 
> Mainline min() still can't do
> 
> 	static const x = min(1, 2);

(second reply having realised what actually fails.)

That is ok.

The code actually falls foul of the type check.
The LHS will be 'signed int' and the RHS 'size_t' which IIRC is
'unsigned int' on 32 bit and 'unsigned long' on 64 bit.

So the comment is explaining the wrong error.
Changing to (size_t)INT_MAX should make min() work.

My new version should let that through, it allows unsigned
against non-negative signed constants.

	David

-
Registered Address Lakeside, Bramley Road, Mount Farm, Milton Keynes, MK1 1PT, UK
Registration No: 1397386 (Wales)
diff mbox series

Patch

--- a/fs/file.c
+++ b/fs/file.c
@@ -25,11 +25,6 @@ 
 #include "internal.h"
 
 unsigned int sysctl_nr_open __read_mostly = 1024*1024;
-unsigned int sysctl_nr_open_min = BITS_PER_LONG;
-/* our min() is unusable in constant expressions ;-/ */
-#define __const_min(x, y) ((x) < (y) ? (x) : (y))
-unsigned int sysctl_nr_open_max =
-	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
 
 static void __free_fdtable(struct fdtable *fdt)
 {
--- a/fs/file_table.c
+++ b/fs/file_table.c
@@ -111,6 +111,12 @@  static int proc_nr_files(struct ctl_table *table, int write, void *buffer,
 	return proc_doulongvec_minmax(table, write, buffer, lenp, ppos);
 }
 
+static const unsigned int sysctl_nr_open_min = BITS_PER_LONG;
+/* our min() is unusable in constant expressions ;-/ */
+#define __const_min(x, y) ((x) < (y) ? (x) : (y))
+static const unsigned int sysctl_nr_open_max =
+	__const_min(INT_MAX, ~(size_t)0/sizeof(void *)) & -BITS_PER_LONG;
+
 static struct ctl_table fs_stat_sysctls[] = {
 	{
 		.procname	= "file-nr",
@@ -134,8 +140,8 @@  static struct ctl_table fs_stat_sysctls[] = {
 		.maxlen		= sizeof(unsigned int),
 		.mode		= 0644,
 		.proc_handler	= proc_dointvec_minmax,
-		.extra1		= &sysctl_nr_open_min,
-		.extra2		= &sysctl_nr_open_max,
+		.extra1		= (void *)&sysctl_nr_open_min,
+		.extra2		= (void *)&sysctl_nr_open_max,
 	},
 	{ }
 };
--- a/include/linux/file.h
+++ b/include/linux/file.h
@@ -113,6 +113,4 @@  int receive_fd_replace(int new_fd, struct file *file, unsigned int o_flags);
 extern void flush_delayed_fput(void);
 extern void __fput_sync(struct file *);
 
-extern unsigned int sysctl_nr_open_min, sysctl_nr_open_max;
-
 #endif /* __LINUX_FILE_H */