[v12,1/3] lib/bitmap: add bitmap_{read,write}()

Commit Message

Alexander Potapenko Nov. 9, 2023, 3:11 p.m. UTC

From: Syed Nayyar Waris <[e-mail]>

The two new functions allow reading/writing values of length up to
BITS_PER_LONG bits at arbitrary position in the bitmap.

The code was taken from "bitops: Introduce the for_each_set_clump macro"
by Syed Nayyar Waris with a number of changes and simplifications:
 - instead of using roundup(), which adds an unnecessary dependency
   on <linux/math.h>, we calculate space as BITS_PER_LONG-offset;
 - indentation is reduced by not using else-clauses (suggested by
   checkpatch for bitmap_get_value());
 - bitmap_get_value()/bitmap_set_value() are renamed to bitmap_read()
   and bitmap_write();
 - some redundant computations are omitted.

Cc: Arnd Bergmann <[e-mail]>
Signed-off-by: Syed Nayyar Waris <[e-mail]>
Signed-off-by: William Breathitt Gray <[e-mail]>
Link: https://lore.kernel.org/lkml/fe[e-mail]/
Suggested-by: Yury Norov <[e-mail]>
Co-developed-by: Alexander Potapenko <[e-mail]>
Signed-off-by: Alexander Potapenko <[e-mail]>
Reviewed-by: Andy Shevchenko <[e-mail]>

---
This patch was previously part of the "Implement MTE tag compression for
swapped pages" series
(https://lore.kernel.org/linux-arm-kernel/[e-mail]/T/)

This patch was previously called "lib/bitmap: add
bitmap_{set,get}_value()"
(https://lore.kernel.org/lkml/[e-mail]/)

v11:
 - rearrange whitespace as requested by Andy Shevchenko,
   add Reviewed-by:, update a comment

v10:
 - update comments as requested by Andy Shevchenko

v8:
 - as suggested by Andy Shevchenko, handle reads/writes of more than
   BITS_PER_LONG bits, add a note for 32-bit systems

v7:
 - Address comments by Yury Norov, Andy Shevchenko, Rasmus Villemoes:
   - update code comments;
   - get rid of GENMASK();
   - s/assign_bit/__assign_bit;
   - more vertical whitespace for better readability;
 - more compact code for bitmap_write() (now for real)

v6:
 - As suggested by Yury Norov, do not require bitmap_read(..., 0) to
   return 0.

v5:
 - Address comments by Yury Norov:
   - updated code comments and patch title/description
   - replace GENMASK(nbits - 1, 0) with BITMAP_LAST_WORD_MASK(nbits)
   - more compact bitmap_write() implementation

v4:
 - Address comments by Andy Shevchenko and Yury Norov:
   - prevent passing values >= 64 to GENMASK()
   - fix commit authorship
   - change comments
   - check for unlikely(nbits==0)
   - drop unnecessary const declarations
   - fix kernel-doc comments
   - rename bitmap_{get,set}_value() to bitmap_{read,write}()
---
 include/linux/bitmap.h | 77 ++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 77 insertions(+)

Comments

Alexander Potapenko Dec. 4, 2023, 1:28 p.m. UTC | #1

On Thu, Nov 9, 2023 at 4:11 PM Alexander Potapenko <[e-mail]> wrote:
>
> From: Syed Nayyar Waris <[e-mail]>
>
> The two new functions allow reading/writing values of length up to
> BITS_PER_LONG bits at arbitrary position in the bitmap.
>
> The code was taken from "bitops: Introduce the for_each_set_clump macro"
> by Syed Nayyar Waris with a number of changes and simplifications:
>  - instead of using roundup(), which adds an unnecessary dependency
>    on <linux/math.h>, we calculate space as BITS_PER_LONG-offset;
>  - indentation is reduced by not using else-clauses (suggested by
>    checkpatch for bitmap_get_value());
>  - bitmap_get_value()/bitmap_set_value() are renamed to bitmap_read()
>    and bitmap_write();
>  - some redundant computations are omitted.
>
> Cc: Arnd Bergmann <[e-mail]>
> Signed-off-by: Syed Nayyar Waris <[e-mail]>
> Signed-off-by: William Breathitt Gray <[e-mail]>
> Link: https://lore.kernel.org/lkml/fe[e-mail]/
> Suggested-by: Yury Norov <[e-mail]>
> Co-developed-by: Alexander Potapenko <[e-mail]>
> Signed-off-by: Alexander Potapenko <[e-mail]>
> Reviewed-by: Andy Shevchenko <[e-mail]>

Yury, Andy, do you think anything else is needed for this series?
If not, whom should we ask to take it?

Yury Norov Dec. 4, 2023, 2:22 p.m. UTC | #2

On Mon, Dec 04, 2023 at 02:28:09PM +0100, Alexander Potapenko wrote:
> On Thu, Nov 9, 2023 at 4:11 PM Alexander Potapenko <[e-mail]> wrote:
> >
> > From: Syed Nayyar Waris <[e-mail]>
> >
> > The two new functions allow reading/writing values of length up to
> > BITS_PER_LONG bits at arbitrary position in the bitmap.
> >
> > The code was taken from "bitops: Introduce the for_each_set_clump macro"
> > by Syed Nayyar Waris with a number of changes and simplifications:
> >  - instead of using roundup(), which adds an unnecessary dependency
> >    on <linux/math.h>, we calculate space as BITS_PER_LONG-offset;
> >  - indentation is reduced by not using else-clauses (suggested by
> >    checkpatch for bitmap_get_value());
> >  - bitmap_get_value()/bitmap_set_value() are renamed to bitmap_read()
> >    and bitmap_write();
> >  - some redundant computations are omitted.
> >
> > Cc: Arnd Bergmann <[e-mail]>
> > Signed-off-by: Syed Nayyar Waris <[e-mail]>
> > Signed-off-by: William Breathitt Gray <[e-mail]>
> > Link: https://lore.kernel.org/lkml/fe[e-mail]/
> > Suggested-by: Yury Norov <[e-mail]>
> > Co-developed-by: Alexander Potapenko <[e-mail]>
> > Signed-off-by: Alexander Potapenko <[e-mail]>
> > Reviewed-by: Andy Shevchenko <[e-mail]>
> 
> Yury, Andy, do you think anything else is needed for this series?
> If not, whom should we ask to take it?

I probably need to revisit it, but generally it looks OK.

But I can't take new API without having real users. Now that your MTE
series is delayed, and Alexander's 'ip_tunnel flags' is not moving as
well, there's non-zero chance to merge dead code.

If you want it to be merged, I'd advise you to walk through the kernel
sources and find good cases where bitmap_read() and bitmap_write() can
be used. Then append this series with such conversions, and I'll be
able to move it.

Thanks,
Yury

Alexander Lobakin Dec. 4, 2023, 3:54 p.m. UTC | #3

From: Yury Norov <[e-mail]>
Date: Mon, 4 Dec 2023 06:22:20 -0800

> On Mon, Dec 04, 2023 at 02:28:09PM +0100, Alexander Potapenko wrote:
>> On Thu, Nov 9, 2023 at 4:11 PM Alexander Potapenko <[e-mail]> wrote:
>>>
>>> From: Syed Nayyar Waris <[e-mail]>
>>>
>>> The two new functions allow reading/writing values of length up to
>>> BITS_PER_LONG bits at arbitrary position in the bitmap.
>>>
>>> The code was taken from "bitops: Introduce the for_each_set_clump macro"
>>> by Syed Nayyar Waris with a number of changes and simplifications:
>>>  - instead of using roundup(), which adds an unnecessary dependency
>>>    on <linux/math.h>, we calculate space as BITS_PER_LONG-offset;
>>>  - indentation is reduced by not using else-clauses (suggested by
>>>    checkpatch for bitmap_get_value());
>>>  - bitmap_get_value()/bitmap_set_value() are renamed to bitmap_read()
>>>    and bitmap_write();
>>>  - some redundant computations are omitted.
>>>
>>> Cc: Arnd Bergmann <[e-mail]>
>>> Signed-off-by: Syed Nayyar Waris <[e-mail]>
>>> Signed-off-by: William Breathitt Gray <[e-mail]>
>>> Link: https://lore.kernel.org/lkml/fe[e-mail]/
>>> Suggested-by: Yury Norov <[e-mail]>
>>> Co-developed-by: Alexander Potapenko <[e-mail]>
>>> Signed-off-by: Alexander Potapenko <[e-mail]>
>>> Reviewed-by: Andy Shevchenko <[e-mail]>
>>
>> Yury, Andy, do you think anything else is needed for this series?
>> If not, whom should we ask to take it?
> 
> I probably need to revisit it, but generally it looks OK.
> 
> But I can't take new API without having real users. Now that your MTE
> series is delayed, and Alexander's 'ip_tunnel flags' is not moving as
> well, there's non-zero chance to merge dead code.

One of the PFCP developers had a quick vacation, we'll send PFCP with
the ip_tunnel bitmap conversion this week.
I'll tell Jakub he'd need to pull boys' tree :D

> 
> If you want it to be merged, I'd advise you to walk through the kernel
> sources and find good cases where bitmap_read() and bitmap_write() can
> be used. Then append this series with such conversions, and I'll be
> able to move it.
> 
> Thanks,
> Yury

Thanks,
Olek

Patch

diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h
index 03644237e1efb..7dd00e2e6d539 100644
--- a/include/linux/bitmap.h
+++ b/include/linux/bitmap.h
@@ -77,6 +77,10 @@  struct device;
  *  bitmap_to_arr64(buf, src, nbits)            Copy nbits from buf to u64[] dst
  *  bitmap_get_value8(map, start)               Get 8bit value from map at start
  *  bitmap_set_value8(map, value, start)        Set 8bit value to map at start
+ *  bitmap_read(map, start, nbits)              Read an nbits-sized value from
+ *                                              map at start
+ *  bitmap_write(map, value, start, nbits)      Write an nbits-sized value to
+ *                                              map at start
  *
  * Note, bitmap_zero() and bitmap_fill() operate over the region of
  * unsigned longs, that is, bits behind bitmap till the unsigned long
@@ -599,6 +603,79 @@  static inline void bitmap_set_value8(unsigned long *map, unsigned long value,
 	map[index] |= value << offset;
 }
 
+/**
+ * bitmap_read - read a value of n-bits from the memory region
+ * @map: address to the bitmap memory region
+ * @start: bit offset of the n-bit value
+ * @nbits: size of value in bits, nonzero, up to BITS_PER_LONG
+ *
+ * Returns: value of @nbits bits located at the @start bit offset within the
+ * @map memory region. For @nbits = 0 and @nbits > BITS_PER_LONG the return
+ * value is undefined.
+ */
+static inline unsigned long bitmap_read(const unsigned long *map,
+					unsigned long start,
+					unsigned long nbits)
+{
+	size_t index = BIT_WORD(start);
+	unsigned long offset = start % BITS_PER_LONG;
+	unsigned long space = BITS_PER_LONG - offset;
+	unsigned long value_low, value_high;
+
+	if (unlikely(!nbits || nbits > BITS_PER_LONG))
+		return 0;
+
+	if (space >= nbits)
+		return (map[index] >> offset) & BITMAP_LAST_WORD_MASK(nbits);
+
+	value_low = map[index] & BITMAP_FIRST_WORD_MASK(start);
+	value_high = map[index + 1] & BITMAP_LAST_WORD_MASK(start + nbits);
+	return (value_low >> offset) | (value_high << space);
+}
+
+/**
+ * bitmap_write - write n-bit value within a memory region
+ * @map: address to the bitmap memory region
+ * @value: value to write, clamped to nbits
+ * @start: bit offset of the n-bit value
+ * @nbits: size of value in bits, nonzero, up to BITS_PER_LONG.
+ *
+ * bitmap_write() behaves as-if implemented as @nbits calls of __assign_bit(),
+ * i.e. bits beyond @nbits are ignored:
+ *
+ *   for (bit = 0; bit < nbits; bit++)
+ *           __assign_bit(start + bit, bitmap, val & BIT(bit));
+ *
+ * For @nbits == 0 and @nbits > BITS_PER_LONG no writes are performed.
+ */
+static inline void bitmap_write(unsigned long *map, unsigned long value,
+				unsigned long start, unsigned long nbits)
+{
+	size_t index;
+	unsigned long offset;
+	unsigned long space;
+	unsigned long mask;
+	bool fit;
+
+	if (unlikely(!nbits || nbits > BITS_PER_LONG))
+		return;
+
+	mask = BITMAP_LAST_WORD_MASK(nbits);
+	value &= mask;
+	offset = start % BITS_PER_LONG;
+	space = BITS_PER_LONG - offset;
+	fit = space >= nbits;
+	index = BIT_WORD(start);
+
+	map[index] &= (fit ? (~(mask << offset)) : ~BITMAP_FIRST_WORD_MASK(start));
+	map[index] |= value << offset;
+	if (fit)
+		return;
+
+	map[index + 1] &= BITMAP_FIRST_WORD_MASK(start + nbits);
+	map[index + 1] |= (value >> space);
+}
+
 #endif /* __ASSEMBLY__ */
 
 #endif /* __LINUX_BITMAP_H */