Re: how to understand this bitmap_zero

2005-11-09 Thread Neil Brown 
On Wednesday November 9, [EMAIL PROTECTED] wrote:
 could anybody help me on this? thanks!
 
 see if we call bitmap_zero(dst, 2), it will do *dst = 0UL and thus clear
 whole *dst, but what if we intent to clear 2 bits? not 32bits?

bitmap_zero isn't intended for zeroing just a few bits in a bitmap.
It is for zeroing an entire bitmap, and you tell it how big the bitmap
is.  So this function will always zero at least the whole bitmap, and
maybe a bit more.  as bitmaps are always allocated as an array of
'unsigned long', there it no risk it over-running the space allocated.

Hope that helps.
NeilBrown

 
 static inline void bitmap_zero(unsigned long *dst, int nbits)
 {
 if (nbits = BITS_PER_LONG)
 *dst = 0UL;
 else {
 int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
 memset(dst, 0, len);
 }
 }
 
 
 Ming
 
 
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Re: how to understand this bitmap_zero

2005-11-09 Thread Ming Zhang 
ic. thx!

so it seems that we still have to use set_bit in a for loop to set
certain particular area, rite?

Ming

On Thu, 2005-11-10 at 09:29 +1100, Neil Brown wrote:
 On Wednesday November 9, [EMAIL PROTECTED] wrote:
  could anybody help me on this? thanks!
  
  see if we call bitmap_zero(dst, 2), it will do *dst = 0UL and thus clear
  whole *dst, but what if we intent to clear 2 bits? not 32bits?
 
 bitmap_zero isn't intended for zeroing just a few bits in a bitmap.
 It is for zeroing an entire bitmap, and you tell it how big the bitmap
 is.  So this function will always zero at least the whole bitmap, and
 maybe a bit more.  as bitmaps are always allocated as an array of
 'unsigned long', there it no risk it over-running the space allocated.
 
 Hope that helps.
 NeilBrown
 
  
  static inline void bitmap_zero(unsigned long *dst, int nbits)
  {
  if (nbits = BITS_PER_LONG)
  *dst = 0UL;
  else {
  int len = BITS_TO_LONGS(nbits) * sizeof(unsigned long);
  memset(dst, 0, len);
  }
  }
  
  
  Ming
  
  
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Re: how to understand this bitmap_zero

2005-11-09 Thread Neil Brown 
On Wednesday November 9, [EMAIL PROTECTED] wrote:
 ic. thx!
 
 so it seems that we still have to use set_bit in a for loop to set
 certain particular area, rite?

Correct.

NeilBrown
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