From 60ef690018b262ddcd0d51edf10e40710deb9c9f Mon Sep 17 00:00:00 2001 From: Yury Norov <ynorov@caviumnetworks.com> Date: Fri, 8 Sep 2017 16:15:41 -0700 Subject: bitmap: introduce BITMAP_FROM_U64() The macro is the compile-time analogue of bitmap_from_u64() with the same purpose: convert the 64-bit number to the properly ordered pair of 32-bit parts, suitable for filling the bitmap in 32-bit BE environment. Use it to make test_bitmap_parselist() correct for 32-bit BE ABIs. Tested on BE mips/qemu. [akpm@linux-foundation.org: tweak code comment] Link: http://lkml.kernel.org/r/20170810172916.24144-1-ynorov@caviumnetworks.com Signed-off-by: Yury Norov <ynorov@caviumnetworks.com> Cc: Noam Camus <noamca@mellanox.com> Cc: Rasmus Villemoes <linux@rasmusvillemoes.dk> Cc: Matthew Wilcox <mawilcox@microsoft.com> Cc: Mauro Carvalho Chehab <mchehab@kernel.org> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org> --- include/linux/bitmap.h | 32 ++++++++++++++++++++++++++++++++ 1 file changed, 32 insertions(+) (limited to 'include') diff --git a/include/linux/bitmap.h b/include/linux/bitmap.h index 5797ca6fdfe2..700cf5f67118 100644 --- a/include/linux/bitmap.h +++ b/include/linux/bitmap.h @@ -360,6 +360,38 @@ static inline int bitmap_parse(const char *buf, unsigned int buflen, return __bitmap_parse(buf, buflen, 0, maskp, nmaskbits); } +/* + * BITMAP_FROM_U64() - Represent u64 value in the format suitable for bitmap. + * + * Linux bitmaps are internally arrays of unsigned longs, i.e. 32-bit + * integers in 32-bit environment, and 64-bit integers in 64-bit one. + * + * There are four combinations of endianness and length of the word in linux + * ABIs: LE64, BE64, LE32 and BE32. + * + * On 64-bit kernels 64-bit LE and BE numbers are naturally ordered in + * bitmaps and therefore don't require any special handling. + * + * On 32-bit kernels 32-bit LE ABI orders lo word of 64-bit number in memory + * prior to hi, and 32-bit BE orders hi word prior to lo. The bitmap on the + * other hand is represented as an array of 32-bit words and the position of + * bit N may therefore be calculated as: word #(N/32) and bit #(N%32) in that + * word. For example, bit #42 is located at 10th position of 2nd word. + * It matches 32-bit LE ABI, and we can simply let the compiler store 64-bit + * values in memory as it usually does. But for BE we need to swap hi and lo + * words manually. + * + * With all that, the macro BITMAP_FROM_U64() does explicit reordering of hi and + * lo parts of u64. For LE32 it does nothing, and for BE environment it swaps + * hi and lo words, as is expected by bitmap. + */ +#if __BITS_PER_LONG == 64 +#define BITMAP_FROM_U64(n) (n) +#else +#define BITMAP_FROM_U64(n) ((unsigned long) ((u64)(n) & ULONG_MAX)), \ + ((unsigned long) ((u64)(n) >> 32)) +#endif + /* * bitmap_from_u64 - Check and swap words within u64. * @mask: source bitmap -- cgit v1.2.3