bio_alloc_bioset — allocate a bio for I/O
| struct bio * fsfuncbio_alloc_bioset ( | gfp_t gfp_mask, | 
| int nr_iovecs, | |
| struct bio_set * bs ); | 
gfp_maskthe GFP_ mask given to the slab allocator
nr_iovecsnumber of iovecs to pre-allocate
bsthe bio_set to allocate from.
   bio_alloc_bioset will try its own mempool to satisfy the allocation.
   If __GFP_WAIT is set then we will block on the internal pool waiting
   for a struct bio to become free.
   
Note that the caller must set ->bi_destructor on successful return of a bio, to do the appropriate freeing of the bio once the reference count drops to zero.